Guía para médicos sobre el uso de pruebas de diagnóstico rápido de influenza | Profesionales de la salud | Influenza estacional (gripe)

Guía para médicos sobre el uso de pruebas de diagnóstico rápido de influenza | Profesionales de la salud | Influenza estacional (gripe)

Guía para médicos sobre el uso de pruebas de diagnóstico rápido de influenza

En esta página

• Antecedentes
• Uso de RIDT en la toma de decisiones clínicas
• Uso de RIDT con fines de salud pública para detectar brotes de influenza
• Factores que influyen en los resultados de las RIDT
• Interpretación de los resultados de las pruebas de diagnóstico rápido de la influenza
• Información sobre la actividad local de la influenza
• Cuándo considerar realizar más pruebas de influenza
• Figura 1
• Figura 2
• Figura 3
• Figura 4
• Tabla 1
• Tabla 2
• Referencias

Antecedentes

Las pruebas de diagnóstico rápido de la influenza (RIDTs) son inmunoensayos que pueden identificar la presencia de antígenos nucleoproteicos virales de la influenza A y B en muestras respiratorias y que exponen el resultado de forma cualitativa (positivo contra negativo) (1). En los Estados Unidos hay varias RIDT disponibles en el mercado. (Ver "Tabla 1: Métodos para detectar virus de influenza" y "Tabla 2: Características de las pruebas de diagnóstico rápido de la influenza".) The reference standards for laboratory confirmation of influenza virus infection in respiratory specimens are reverse transcription-polymerase chain reaction (RT-PCR) or viral culture. Las RIDT pueden dar resultados en un marco de tiempo clínicamente relevante, es decir, aproximadamente 20 minutos o menos. However, RIDTs have limited sensitivity to detect influenza virus in respiratory specimens compared to RT-PCR or viral culture and negative RIDT test results should be interpreted with caution given the potential for false negative results, especially during peak influenza activity in a community. Some RIDTs use analyzer reader devices to standardize result interpretation.

1 Las pruebas de diagnóstico rápido de la influenza (RIDT) no incluyen ensayos moleculares de detección rápida. Los ensayos moleculares de diagnóstico rápido son un nuevo tipo de prueba de diagnóstico de la influenza que utilizan la amplificación isotérmica de ácido nucleico para la detección del virus. En este momento, existe un solo ensayo molecular de diagnóstico rápido aprobado por la FDA para usar en los Estados Unidos.

Ventajas y desventajas de las RIDT

Ventajas

• Producen resultados rápidos en 15 minutos o menos, fáciles de implementar
• Some RIDTs are cleared for office/bedside use. RIDTs that have been CLIA waived can be used in settings that may include point-of-care.

Desventajas

• Sensibilidad de calidad inferior ante las pruebas, los resultados de falsos negativos son frecuentes, especialmente cuando la actividad de la influenza es alta
• Although specificity is high, false positive results can also occur, especially during times when influenza activity is low.
• Some RIDTs distinguish between influenza A or B viruses  while others do not. RIDTs that provide results on type of influenza virus (e.g., influenza A or B virus), do not provide information on influenza A virus subtype [e.g., A(H1N1)pdm09 versus A(H3N2)] or specific virus strain information (e.g., degree of similarity to vaccine strains)

 Arriba

Uso de RIDT en la toma de decisiones clínicas

Las RIDT se pueden usar para ayudar a tomar decisiones sobre el diagnóstico y el tratamiento para pacientes en entornos clínicos, como si se deben recetar o no medicamentos antivirales. However, due to the limited sensitivities, los resultados negativos de las RIDT no excluyen la infección por virus de influenza en pacientes con signos y síntomas que sugieren influenza. Therefore, antiviral treatment should not be withheld from patients with suspected influenza, even if they test negative by RIDT and further influenza testing of respiratory specimens by molecular assays may be indicated. Más información acerca de los medicamentos antivirales y recomendaciones sobre su uso.

No es necesario hacer pruebas a todos los pacientes con signos y síntomas de influenza para tomar decisiones sobre tratamientos antivirales (ver Figuras 1-4). Una vez documentada la actividad de la influenza en la comunidad o en la zona geográfica, se puede realizar un diagnóstico clínico de la influenza para pacientes ambulatorios con signos y síntomas coherentes con sospechas de influenza, especialmente durante períodos de picos máximos de influenza en la comunidad.

 Arriba

Uso de RIDT con fines de salud pública para detectar brotes de influenza

RIDTs can be useful to identify influenza virus infection as a cause of respiratory outbreaks in any setting, but especially in institutions (i.e., nursing homes, chronic care facilities, and hospitals), cruise ships, summer camps, schools, etc. Positive RIDT results from one or more ill persons with suspected influenza can support decisions to promptly implement infection prevention and control measures for influenza outbreaks. Sin embargo, los resultados negativos no excluyen la infección por virus de influenza como causa de un brote de problemas respiratorios debido a la sensibilidad limitada de estas pruebas. Si se analizan muestras respiratorias de varias personas que se piensa padecen influenza se aumentarán las posibilidades de detectar una infección por virus de influenza si esta es la causa del brote. Public health authorities should be notified promptly of any suspected institutional outbreak and respiratory specimens should be collected from ill persons (whether positive or negative by RIDT) and sent to a public health laboratory for more accurate influenza testing by molecular assays and viral culture.

 Arriba

Factores que influyen en los resultados de las RIDT

Muchos factores pueden influir en la precisión de las RIDT:

• Signos y síntomas clínicos que concuerdan con la influenza
  • Tener signos y síntomas clínicos que concuerdan con la influenza aumenta la probabilidad de infección por virus de influenza antes de realizar las pruebas, lo cual aumenta la fiabilidad de un resultado positivo de la RIDT.
• Prevalencia de la actividad de la influenza en la población analizada
  • La actividad de la influenza varía cada temporada, lo cual afecta directamente a los valores predictivos de las RIDT (ver los siguientes algoritmos [Figuras 3 y 4], y Estrategias para la prevención de la influenza estacional en los cuidados de la salud.)
• Tiempo desde la aparición de la enfermedad hasta la recolección de muestras respiratorias para analizar
  • Testing specimens collected within 3-4 days of illness onset (when influenza viral shedding is highest) is more likely to yield positive RIDT results if the patient has influenza.
• Tipo de muestra respiratoria analizada
  • RIDTs have different specifications for acceptable specimens (e.g., nasopharyngeal, nasal or throat swab/aspirate). Se deben leer las instrucciones de empleo de las prueba RIDT utilizadas para asegurar que se recoge una muestra apropiada y que se sigue el procedimiento para su análisis. Algunas pruebas pueden requerir que se recolecten las muestras usando un hisopo especial (algunas RIDT se deben usar con un hisopo proporcionado en el kit de pruebas; el material de algunos hisopos puede interferir en los resultados de las RIDT).
  • Las RIDT además deben garantizar que se usa el medio de transporte viral u otro medio apropiado, de acuerdo a las especificaciones de la prueba, si la prueba se realiza en un lugar diferente a donde se recolectó la muestra del paciente.
  • Collection of good quality respiratory specimens (e.g., nasopharyngeal or nasal swab/aspirate/wash or combined nasal/throat swab specimens) also will increase the accuracy of RIDT results.
  • Algunas RIDT exigen que se use en la prueba toda la muestra recogida. Debe considerarse la recolección de una segunda muestra para una prueba confirmatoria usando cultivo viral o RT-PCR.
• Precisión de la prueba comparada con una prueba de referencia ("estándar de oro" = RT-PCR o cultivo viral)
  • Sensibilidad de las RIDT
    • Proporción de resultados positivos de la RIDT entre todos los resultados positivos de la "prueba de estándar de oro" (RT-PCR o cultivo viral)
    • Característica fija de una prueba; normalmente de baja a moderada (10-70%)para las RIDT
      • An RIDT with low sensitivity will produce negative results in some patients with influenza (false negatives)
• Especificidad de la RIDT
  • Proporción de resultados negativos de la RIDT entre todos los resultados negativos de la "prueba de estándar de oro" (RT-PCR o cultivo viral)
  • Característica fija de una prueba; normalmente muy alta para las RIDT (90-95%)
    • An RIDT with low sensitivity will produce negative results in some patients with influenza (false negatives)

 Arriba

Interpretación de los resultados de las pruebas de diagnóstico rápido de la influenza

Proper interpretation of RIDT results is very important for clinical management of patients and for assessing suspected influenza outbreaks. The accuracy  of RIDTs depends largely on the conditions under which they are used. El comprender algunos factores básicos puede minimizar las confusiones causadas por resultados falso-positivos o falso-negativos.

• Sensitivities of RIDTs are generally approximately 50-70%, but a range of 10-80% has been reported compared to viral culture or RT-PCR. Las especificidades de las RIDT son aproximadamente del 90-95% (índice del 85-100%). Por ello, los resultados negativos falsos ocurren más a menudo que los resultados positivos falsos.
  • Los resultados negativos de las RIDT no excluyen una infección por virus de influenza y se debe seguir considerando la posibilidad de influenza en un paciente si la sospecha clínica es alta basándose en antecedentes, signos, síntomas y examen clínico.
• Un resultado positivo en una persona que recibió recientemente la administración intranasal de la vacuna viva atenuada en atomizador nasal (LAIV) puede indicar la detección del virus de la vacuna. LAIV contains influenza virus strains that undergo viral replication in respiratory tissues of lower temperature (e.g., nasal passages) than internal body temperature. Debido a que las fosas nasales se infectan con las cepas vivas del virus de la influenza de la vacuna durante la administración de LAIV, las muestras de las fosas nasales extraídas unos días después de la vacunación con LAIV pueden causar resultados positivos de influenza. Puede ser posible detectar cepas de la vacuna LAIV hasta 7 días después de la vacunación y, en casos menos frecuentes, por períodos mayores.
• Es más probable que se produzcan resultados falso-positivos (y verdadero-negativos) cuando la prevalencia de la enfermedad en la comunidad es baja, lo que normalmente ocurre al principio y al final de la temporada de influenza y durante el verano.
  • El valor predictivo negativo de una RIDT (la proporción de pacientes con resultados negativos que no tienen influenza) es más alto cuando la actividad de la influenza es baja.
  • El valor predictivo positivo de una RIDT (la proporción de pacientes con resultados positivos que tienen influenza) es más baja cuando la actividad de la influenza es baja.
• Es más probable que se produzcan resultados falso-negativos (y verdaderos positivos) cuando la prevalencia de la enfermedad en la comunidad es alta.
  • El valor predictivo positivo de una RIDT (la proporción de pacientes con resultados positivos que tienen influenza) es más alto cuando la actividad de la influenza es alta
  • El valor predictivo negativo de una RIDT (la proporción de pacientes con resultados negativos que no tienen influenza) es más baja cuando la actividad de la influenza es alta

Minimizar resultados falsos

• Recolecte las muestras lo antes posible durante la enfermedad (lo ideal es menos de 4 días desde la aparición de la enfermedad).
• Siga las instrucciones del fabricante, incluso para muestras aceptables y su manipulación.
• Haga un seguimiento de los resultados negativos con pruebas confirmatorias (RT-PCR o cultivo viral) si se desea obtener un diagnóstico de influenza confirmado por un laboratorio.

 Arriba 

Los médicos clínicos deben ponerse en contacto con el departamento de salud de su localidad o estado para obtener información sobre la actividad actual de la influenza. Para obtener más información acerca de la actividad de la influenza en los Estados Unidos durante la temporada de influenza, visite elInforme semanal de vigilancia de la influenza en los EE. UU. (FluView).

Cuándo considerar realizar más pruebas de influenza

Considere enviar muestras respiratorias para pruebas de influenza por cultivo viral o RT-PCR para confirmar los resultados de una RIDT cuando:

• Las pruebas de un paciente son negativas cuando la actividad de la influenza en la comunidad es alta y se desea tener una confirmación de un laboratorio.
• Las pruebas de un paciente son positivas cuando la prevalencia de influenza en la comunidad es baja y se tiene en cuenta un resultado positivo falso.
• A patient has had recent close exposure to pigs or poultry or other animals and novel influenza A virus infection is possible (e.g., influenza A viruses circulate widely among swine and birds, including poultry, and also can infect other animals such as horses and dogs)

Pacientes hospitalizados

Se recomienda hacer las pruebas de influenza en caso de pacientes hospitalizados con presunto diagnóstico de influenza. Molecular assays such as RT-PCR are recommended for testing hospitalized patients, especially if RIDTs are used and yield negative results. However, empiric antiviral treatment should be initiated as soon as possible for hospitalized patients with suspected influenza without the need to wait for any influenza testing results (seeMedicamentos antivirales, información para profesionales de los cuidados de salud). No se debe detener el tratamiento antiviral basándose en resultados negativos de la RIDT dada la limitada sensibilidad de las RIDT. Infection prevention and control measures should be implemented immediately upon admission for any hospitalized patient with suspected influenza even if RIDT results are negative (see Estrategias para la prevención de la influenza estacional en los cuidados de la salud). Se pueden analizar las muestras respiratorias para influenza con inmunofluorescencia, RT-PCR o cultivo viral. Serology for influenza should not be performed for clinical management. Clinicians should understand that negative results of influenza testing do not exclude influenza virus infection, especially if the time from illness onset to collection of respiratory specimens is more than 3  days, or if upper respiratory specimens were tested and the patient has lower respiratory tract disease. If influenza is suspected, testing of clinical specimens collected from different respiratory sites can be done (e.g., upper and lower respiratory tract) and can be collected on more than one day to increase likelihood of influenza virus detection; intubated patients should have endotracheal aspirate specimens tested if influenza is suspected, but not yet confirmed.

Detection of influenza virus infection and prompt implementation of infection prevention and control measures is critical to prevention of nosocomial influenza outbreaks. Cuando hay actividad de la influenza en la comunidad los médicos deberían considerar hacer pruebas de influenza, incluido cultivo viral, en pacientes que desarrollan signos y síntomas de influenza mientras están en un centro de servicios de salud. This should be done as part of a broader surveillance strategy for influenza as discussed in Prevention Strategies for Seasonal Influenza in Heath Care Settings.

Posibles brotes de influenza en instituciones

Cuando se piensa que hay presencia de brotes de influenza en instituciones se deben recolectar muestras respiratorias de pacientes sospechosos de tener influenza lo antes posible desde que hay sospecha de un brote (ver Figura 2). The use of influenza molecular assays is preferred. If RIDTs are used in these settings, clinical specimens should also be sent for influenza testing by viral culture and RT-PCR to provide detailed information on specific influenza A virus subtypes and strains, and antiviral susceptibility data and to verify RIDT test results. Active daily surveillance for suspected influenza illness and collection of specimens from patients with suspected influenza should continue through at least 2 weeks after implementation of control measures to assess effectiveness of the measures and to monitor for potential emergence of antiviral resistance. Ver Estrategias para la prevención de la influenza estacional en los cuidados de la salud.

Vigilancia de la influenza

Laboratory-based surveillance for influenza viruses by viral culture is critically important to the selection of viruses for the next season's influenza vaccine. Virus isolates are needed in order to characterize the circulating influenza A virus subtypes and influenza A and B virus strains and to determine how well they are matched antigenically to vaccine strains. Isolates are also needed for obtaining information on the emergence and prevalence of antiviral resistant strains, and the identification of human infection with novel influenza A virus (e.g., an influenza A virus of animal origin that may sporadically  cause illnesses in people) that may have pandemic potential. This information is needed from specimens sent for viral culture and RT-PCR year round for identification of novel influenza A virus strains or antigenically-drifted  strains, including during times of low influenza activity such as at the beginning and end of influenza seasonal activity. Para obtener más información acerca de la actividad de la influenza en los Estados Unidos durante la temporada de influenza, visite el Informe semanal de vigilancia de la influenza en los EE. UU. (FluView).

 Arriba

Figura 1: Guía para considerar realizar pruebas de diagnóstico del virus de la influenza en pacientes individuales cuando hay virus de influenza circulando en la comunidad1

En la Figura 1, comenzar preguntando ¿El paciente tiene signos y síntomas clínicos compatibles con influenza?2

Si la respuesta es SÍ, preguntar ¿Los resultados de las pruebas de diagnóstico de la influenza* cambiarán el cuidado clínico del paciente?3 (especialmente para pacientes hospitalizados y con enfermedades de alto riesgo4) O ¿influirán en la práctica clínica de otros pacientes?5 *No se debe demorar el tratamiento antiviral, si está indicado clínicamente, en espera de los resultados de las pruebas.

Si la respuesta es SÍ, considerar realizar pruebas de diagnóstico de la influenza. (Ver Tabla 1 para revisar los métodos para detectar virus de influenza; yTabla 2 para revisar las RIDT disponibles).

Si la respuesta es SÍ, interpretar los resultados de las pruebas para la influenza. (Ver Figura 3 para las RIDT).

Si la respuesta es NO para cualquier caso, probablemente no deben indicarse las pruebas de diagnóstico de la influenza.

1. No es necesario confirmar una infección por virus de influenza por medio de pruebas diagnósticas para tomar decisiones clínicas sobre la prescripción de medicamentos antivirales. Decisions to administer antiviral medications for influenza treatment or chemoprophylaxis, if indicated, should be based upon clinical illness and epidemiologic factors, and start of antiviral therapy should not be delayed pending testing results. Respiratory specimens should be collected from an ill patient as early as possible after onset of symptoms (ideally <48-72 hours after onset) to help maximize influenza testing sensitivity.
2. Influenza like-illness (history of feverishness or documented fever with either cough or sore throat), fever with other respiratory symptoms, etc. Note that some persons may have atypical presentations (e.g., elderly, very young infants, immunosuppressed, and patients with certain chronic medical conditions). Fever is not always present (e.g., premature infants, young infants, elderly, immunosuppressed). Otros síntomas asociados con influenza pueden ser mialgias, dolor de cabeza o fatiga. Complications include exacerbation of underlying chronic disease, (e.g., congestive cardiac failure, asthma), pneumonia, bacterial co-infection, bronchiolitis, croup, encephalopathy, encephalitis, seizures, myositis, and others.
3. e.g., Decisions on use of antibiotics or antiviral medications, on conducting further diagnostic tests, on recommendations for home care, or on recommendations for ill persons living with persons with high-risk conditions. Consulte a IDSA, ATS, guía de AAP de antibióticos.
4. Persons aged >65 years or <2 years; pregnant women; persons with chronic lung disease (including asthma), heart disease, renal, metabolic, hematologic and neurologic disease; immunosuppression; and morbid obesity.
5. e.g., Decisions on changing infection prevention and control practices (such as in hospitalized patients); if a positive influenza test result is used for confirming influenza virus circulation in the community which might inform clinical practices related to home care guidance, hospital infection control practices, future testing practices, etc.

 Arriba

Figura 2: Guía para usar las pruebas de diagnóstico del virus de la influenza para investigar brotes en entornos institucionales u otros entornos cerrados1

In Figure 2, start by asking: “Are there 2 or more persons with onset within 2-3 days of each other2 currently with clinical signs and symptoms compatible with influenza virus infection?”3

If YES, ask Will the results of influenza virus testing change outbreak control strategies in the population?4 OR Does the setting include persons at high risk of influenza complications should they become infected (e.g., LTCFs)?5

Si la respuesta es SÍ, considerar realizar pruebas de diagnóstico de la influenza. (Ver Tabla 1 para revisar los métodos para detectar virus de influenza; y la Tabla 2 para revisar las RIDT disponibles).

Si la respuesta es SÍ, interpretar los resultados de las pruebas para la influenza. (Ver Figura 3 para las RIDT).

Si la respuesta es NO para cualquier caso, probablemente no deben indicarse las pruebas de diagnóstico de la influenza.

1. Ejemplos de entornos institucionales o cerrados: centros de cuidados a largo plazo, asilos de ancianos, escuelas, instituciones correccionales, hospitales, barcos.
2. In settings where persons at high-risk of influenza complications reside, a single case of suspected influenza is sufficient for triggering influenza testing and consideration of implementation of empiric infection prevention and control measures, including active surveillance for new illness cases.
3. e.g., Influenza like-illness (fever with either cough or sore throat), fever with other respiratory symptoms, etc. Note that some persons may have atypical presentations (e.g., elderly, very young infants, immunosuppressed, and patients with certain chronic medical conditions). No siempre se presenta fiebre. Otros síntomas asociados con influenza pueden ser mialgias, dolor de cabeza o fatiga. Complications include exacerbation of underlying chronic disease, (e.g., congestive cardiac failure, asthma), pneumonia, bacterial co-infection, bronchiolitis, croup, encephalopathy, encephalitis, seizures, myositis, and others.
4. e.g., use of antivirals empirically for treatment or for chemoprophylaxis of influenza, changes in infection prevention and control practices (isolation or cohorting of ill, quarantine of exposed), changes in admission or staffing policies, or changes in social distancing recommendations, etc.
5. Persons aged >65 years or <2 years; pregnant women; persons with chronic lung disease (including asthma), heart disease, renal, metabolic, hematologic and neurologic disease; immunosuppression; and morbid obesity.
6. In an outbreak setting, RT-PCR or other molecular assays are preferred. Because of the low sensitivity of RIDTs, use of the tests on specimens from more than one ill person is recommended. La presencia de cualquier positivo de influenza entre personas con enfermedades clínicamente compatibles respalda la influenza como causa probable del brote. Negative RIDT results do not exclude influenza virus infection. Confirmation of RIDT results by more RT-PCR  or viral culture specific influenza testing is indicated.

 Arriba

Figura 3: Algoritmo para ayudar en la interpretación de los resultados de las RIDT y en la toma de decisiones médicas durante períodos cuando hay virus de influenza circulando en la comunidad1

En la Figura 3, si la RIDT es POSITIVA para uno de los siguientes tipos de influenza: influenza A, influenza B, o influenza A y B (A/B) la interpretación es:posible infección por virus de influenza.1,2 Deben tomarse medidas tratamiento antiviral para influenza si está indicado clínicamente. Considerar pruebas adicionales para el virus de influenza para confirmar los resultados de la RIDT, para subclasificar el virus de influenza A, para distinguir entre los virus de influenza A y B o para hacer análisis más específicos, si está indicado. Considere realizar pruebas de diagnóstico adicionales para otros microbios patógenos o terapia antibiótica empírica para coinfección bacteriana, si está indicado3.

En la Figura 3, si la RIDT es NEGATIVA para uno de los siguientes tipos de influenza: influenza A, influenza B, o influenza A y B (A/B) la interpretación es: no se puede descartar infección por virus de influenza.1,2 Las medidas a tomar son: usar los signos y síntomas clínicos, antecedentes, examen clínico, información sobre la actividad local de la influenza en la comunidad para decidir si el tratamiento antiviral es el indicado. No usar los resultados negativos de la RIDT exclusivamente para tomar decisiones clínicas o decisiones sobre la salud pública, incluida la identificación de brotes de influenza, o para tomar decisiones sobre las medidas de control de infecciones. Considere realizar pruebas de diagnóstico adicionales para otros microbios patógenos o terapia antibiótica empírica para coinfección bacteriana, si está indicado3.

1. Durante períodos en que la actividad de la influenza es alta y los virus de la influenza está circulando entre las personas de la comunidad (ver 3. a continuación), el valor predictivo positivo del resultado de una prueba es alto (es decir, la posibilidad de que un resultado positivo indique que el paciente tiene influenza es alta), y el valor predictivo negativo del resultado de una prueba es bajo (la posibilidad de que un resultado negativo sea un verdadero negativo es baja) debido a la baja sensibilidad de las RIDT para detectar virus de influenza en muestras respiratorias comparadas con RT-PCR o cultivo viral: los resultados falso negativos son frecuentes.
2. Influenza virus infection may include seasonal influenza A (H3N2), A(H1N1)pdm09, influenza B, or rarely, a novel influenza A virus infection. La interpretación de las RIDT dependerá, en parte, de la prueba que se ha usado - algunas detectarán influenza A, otras detectarán influenza B y otras detectarán tanto virus A como B. Si ambas pruebas, para influenza A y B, son positivas, remita la muestra a un laboratorio de la salud pública para su resolución, ya que las infecciones duales no son frecuentes.
3. Consult local or state health departments or other sources (e.g., virology testing at a local hospital) for local activity on other respiratory pathogens associated with acute respiratory illness. La cobertura antibiótica empírica debe incluir Streptococcus pneumoniae, Staphylococcus aureus (incluido MRSA), Streptococcus grupo A y otros, especialmente para pacientes adultos hospitalizados según las indicaciones de IDSA/ATS CAP.

 Arriba

Figura 4: Algoritmo para ayudar en la interpretación de los resultados de las RIDT y en la toma de decisiones médicas durante períodos en que no hay virus de influenza circulando o la actividad de la influenza es baja en la comunidad1

In Figure 4, if the RIDT is POSITIVE for one of the following: Influenza A, Influenza B, or Influenza A and B (A/B) then the interpretation is Cannot exclude false positive result.1,2 Actions are to use clinical signs, symptoms, history, examination, information on local influenza activity in the community to decide if tratamiento antiviral is indicated. Additional influenza virus testing by RT-PCR or other molecular assays is recommended to confirm RIDT results, for subtyping of influenza A virus, to distinguish between influenza A and B viruses, or for more specific analyses, if indicated. Considere realizar pruebas de diagnóstico adicionales para otros microbios patógenos o terapia antibiótica empírica para coinfección bacteriana, si está indicado3.

En la Figura 4, si la RIDT es NEGATIVA para uno de los siguientes tipos de influenza: influenza A, influenza B, o influenza A y B (A/B) la interpretación es: no se puede descartar infección por virus de influenza.1,2 Las medidas a tomar son: usar los signos y síntomas clínicos, antecedentes, examen clínico, información sobre la actividad local de la influenza en la comunidad para decidir si el tratamiento antiviral es el indicado. No usar los resultados negativos de la RIDT exclusivamente para tomar decisiones clínicas o decisiones sobre la salud pública, incluida la identificación de brotes de influenza, o para tomar decisiones sobre las medidas de control de infecciones. Considere realizar pruebas de diagnóstico adicionales para otros microbios patógenos o terapia antibiótica empírica para coinfección bacteriana, si está indicado3.

1. Durante períodos en que la actividad de la influenza es baja y hay baja circulación de virus de influenza circulando entre las personas de la comunidad, el valor predictivo positivo de una prueba de diagnóstico rápido de influenza es bajo (es decir, la posibilidad de que un resultado positivo indique que el paciente tiene influenza es baja) y el valor predictivo negativo es alto (la posibilidad de que un resultado negativo sea verdadero negativo es alta). Aunque las RIDT tienen una especificidad alta, los resultados falso positivos son más frecuentes cuando la actividad de la influenza es baja.
2. Influenza virus infection may include seasonal influenza A (H3N2), A(H1N1)pdm09, influenza B, or rarely, a novel influenza A virus infection. La interpretación de las RIDT dependerá, en parte, de la prueba que se ha usado - algunas detectarán influenza A, otras detectarán influenza B y otras detectarán tanto virus A como B. Si ambas pruebas, para influenza A y B, son positivas, remita la muestra a un laboratorio de la salud pública para su resolución, ya que las infecciones duales no son frecuentes.
3. Consult local or state health departments or other sources (e.g., virology testing at a local hospital) for local activity on other respiratory pathogens associated with acute respiratory illness. La cobertura antibiótica empírica debe incluir Streptococcus pneumoniae, Staphylococcus aureus (incluido MRSA), Streptococcus grupo A y otros, especialmente para pacientes adultos hospitalizados según las indicaciones de IDSA/ATS CAP.

 Arriba

Tabla 1: Métodos para detectar virus de influenza

Método1	Tipos detectados	Muestras aceptables2	Duración de la prueba	Certificado por la CLIA3
Cultivo celular viral (convencional)	A y B	Hisopado NP4, hisopado de garganta, lavado NP2 o bronquial, aspirado nasal o endotraqueal, esputo	3-10 días	No
Cultivo celular rápido (tubos de ensayo; mezclas celulares)	A y B	Como arriba	1-3 días	No
Immunofluorescence, Direct (DFA) or Indirect (IFA) Antibody Staining [antigen detection]	A y B	Hisopado o lavado NP4, lavado bronquial, aspirado nasal o endotraqueal	1-4 hrs.	No
RT-PCR5 (singleplex y multiplex; en tiempo real y otro basado en el ARN) y otros ensayos moleculares	A y B	Hisopado NP4, hisopado de garganta, lavado NP2 o bronquial, aspirado nasal o endotraqueal, esputo	Varied (Generally ≤15 minutes-6 hours)7	No
Rapid Molecular Assay	A y B	NP4 swab, nasal aspirate, wash, swab	≤15 minutes7	Yes/No7
Rapid Influenza Diagnostic Tests6 (antigen detection)	A y B	Hisopado NP4, (hisopado faríngeo), lavado nasal, aspirado nasal	<30 min.	Sí/No

1. Las pruebas serológicas (detección de anticuerpos) no están recomendadas para el diagnóstico rutinario de pacientes.
2. Ref: Leland, et al. 2007, Clin Micro Rev 20: 49-78. Las muestras respiratorias aprobadas varían en ensayos de influenza autorizados por la FDA.
3. Ref.: http://www.cms.gov/Regulations-and-Guidance/Legislation/CLIA/index.html
4. NP = nasofaríngeo
5. Reacción en cadena de la polimerasa con transcriptasa inversa, incluidos sistemas de pruebas autorizados por la FDA, pruebas de laboratorio de referencia ASR o reactivos desarrollados en laboratorio.
6. Cromatografía o flujo lateral basado en fluorescencia e inmunoensayos basados en la membrana
7. Rapid molecular assays can provide results in 15 minutes or less.  Alere i Influenza A&B was cleared by FDA for nasal swabs and viral transport media.  Alere i Influenza A&B was CLIA-waived only for use with nasal swabs.

 Arriba

Tabla 2: Características de las pruebas de diagnóstico rápido de la influenza1

Procedimiento (Fabricante/Distribuidor)	Virus de la influenza Tipos detectados	Muestras aprobadas2	Certificado por la CLIA3	Uses Analyzer Reader Device
Alere™ i Influenza A/B (Alere Scarborough, Inc.)	A y B	Hisopado nasal (in VTM8)	No	Sí
Alere™ i Influenza A/B4 (CLIA Waived) (Alere Scarborough, Inc.)	A y B	Nasal swab (Direct)	Sí	Sí
BD Directigen™ EZ Flu A+B4 (Becton-Dickinson & Co.)	A y B	Lavado/aspirado/hisopado nasal NP5 Hisopado faríngeo	No	No
BD Veritor™ System for Rapid Detection of Flu A+B4 (CLIA-waived), (Becton Dickinson & Co.)	A y B	NP5 swab/ nasal swab	Sí	Sí
BD Veritor™ System for Rapid Detection of Flu A+B4 (Moderately Complex), (Becton Dickinson & Co.)	A y B	NP5 wash/aspirate	No	Sí
Binax NOW® Influenza A&B4 Test (Binax, Inc.)	A y B	Hisopado NP5, Lavado/aspirado/hisopado nasal	Sí	No
BioSign® para influenza A+B4 o OraSure QuickFlu Rapid A+B Test o Polymedco Poly stat Flu A&B Test o LifeSign LLC Status Flu A&B (Princeton BioMedtech Corp.)	A y B	Hisopado/aspirado/lavado NP5, lavado nasal	No	No
ClearView Exact II Influenza A&B Test o Alere Influenza A&B Test (Binax d/b/a Inverness Medical Alere Scarborough, Inc.)	A y B	Hisopado nasal	Sí	No
Genzyme OSOM® Influenza A&B4 Test (Genzyme Corp.)	A y B	Hisopado nasal	No	No
QuickVue® Influenza A/B Test6 (Quidel Corp.)	A y B	Lavado/aspirado/hisopado nasal	Sí	No
QuickVue® para prueba de influenza A+B4 (Quidel Corp.)	A y B	Hisopado NP5 Lavado/aspirado/hisopado nasal	Sí	No
RAMP Influenza A/B Assay o 3M™ Rapid Detection Flu A+B Test4 (Response Biomedical Corp.)	A y B	Hisopado/aspirado NP5 Lavado/aspirado nasal	No	Sí
SAS™ FluAlert A&B Test (SA Scientific, Inc.)	A y B	Lavado/aspirado nasal	No	No
SAS™ Influenza A4 Test (SA Scientific, Inc.)	solo A	Lavado/aspirado nasal	Sí	No
SAS™ Influenza B6 Test (SA Scientific, Inc.)	Solo B	Lavado/aspirado nasal	Sí	No
Sofia® Analyzer and Influenza A+B FIA (CLIA-waived) (Quidel Corp.)	A y B	Hisopado NP5 Hisopado nasal	Sí	Sí
Sofia® Analyzer and Influenza A+B4,7, FIA (Quidel Corp.)	A y B	Aspirado/hisopado/lavado NP5 Hisopado nasal	No	Sí
TRU FLU®4 (Meridian Bioscience, Inc.)	A y B	Aspirado/hisopado NP5 Lavado/hisopado nasal	No	No
XPECT™ Influenza A/B4 (Remel Inc./Thermo Fisher Scientific)	A y B	Lavado/hisopado nasal Hisopado faríngeo	No	No

Versión en PDF para imprimir[218 KB, 3 páginas]

 Arriba

1. Esta lista puede no incluir todos los equipos de prueba aprobados por la Administración de Alimentos y Medicamentos de EE. UU. Pruebas discontinuas no incluidas.
2. Muestras respiratorias aprobadas según las instrucciones del fabricante. Tenga en cuenta que el resultado de la prueba puede variar si se usan otras muestras respiratorias.
3. Ref.: http://www.cms.gov/Regulations-and-Guidance/Legislation/CLIA/index.html
4. Distingue entre las infecciones con los virus A y B de influenza.
5. NP = nasofaríngeo.
6. No distingue entre las infecciones con los virus A y B de influenza cuando se la usa aisladamente.
7. Requiere un dispositivo lector analizador separado.
8. VTM = viral transport media

Descargo de responsabilidad: El uso de nombres y fuentes comerciales es con fines de identificación solamente y no implica aprobación por parte de los Centros para el Control y la Prevención de Enfermedades o el Departamento de Salud y Servicios Humanos.

Referencias

Ali T, Scott N, Kallas W, Halliwell ME, Savino C, Rosenberg E, Ferraro M, Hohmann E. Detection of influenza antigen with rapid antibody-based tests after intranasal influenza vaccination (FluMist). Clin Infect Dis. 1 de marzo de 2004 ;38(5):760-2.

Balish A, Garten R, Klimov A, Villanueva J. Analytical detection of influenza A(H3N2)v and other A variant viruses from the USA by rapid influenza diagnostic tests. Influenza: otros virus respiratorios. 2012 de sept. de 18. doi: 10.1111/irv.12017. [publicación electrónica previa a la edición impresa]

Bell J, Bonner A, Cohen DM, Birkhahn R, Yogev R, Triner W, Cohen J, Palavecino E, Selva-rangan R. Multicenter clinical evaluation of the novel Alere™ i Influenza A&B isothermal nucleic acid amplification test. J Clin Virol. 2014 Sep;61(1):81-6.

Block SL, Yogev R, Hayden FG, Ambrose CS, Zeng W, Walker RE. Shedding and immunogenicity of live attenuated influenza vaccine virus in subjects 5-49 years of age. Vaccine. 8 de sept. de 2008 ;26(38):4940-6.

Centros para el Control y la Prevención de Enfermedades (CDC). Evaluación de pruebas de diagnóstico rápido del virus de la influenza A (H3N2)v y recuento actualizado de los casos - Estados Unidos, 2012. Informe semanal de morbilidad y mortalidad (MMWR). 17 de agosto de 2012;61(32):619-21.

Centros para el Control y la Prevención de Enfermedades (CDC). Evaluación de 11 pruebas de diagnóstico rápido de la influenza, disponibles en el mercado - Estados Unidos, 2011-2012. Informe semanal de morbilidad y mortalidad (MMWR) 2 de noviembre de 2012;61:873-6.

Chartrand C, Leeflang MM, Minion J, Brewer T, Pai M. Accuracy of rapid influenza diagnostic tests: a meta-analysis. Ann Intern Med. 3 de abril de 2012;156(7):500-11.

Comité de Enfermedades Infecciosas, Academia Estadounidense de Pediatría. Declaración de intenciones - Recomendaciones para la prevención y el control de la influenza en niños, 2010-2011..

Harper SA, Bradley JS, Englund JA, File TM, Gravenstein S, Hayden FG et al. Influenza estacional en adultos y niños - Diagnóstico, tratamiento, quimioprofilaxis y manejo institucional del brote: pautas de práctica médica de la Sociedad Estadounidense de Enfermedades Infecciosas. Clin Infect Dis.15 de abril de 2009;48(8):1003-32.

Hazelton B, Gray T, Ho J, Ratnamohan VM, Dwyer DE, Kok J. Detection of influenza A and B with the Alere i Influenza A & B: a novel isothermal nucleic acid amplification assay. Influenza and Other Respiratory Viruses 2015;9(3):151-4.

Organización Mundial de la Salud. Guía de la OMS sobre el manejo farmacológico del virus de la influenza pandémica A (H1N1) 2009 y otros virus de la influenza. Modificado en febrero de 2010[540KB, 32 páginas].

Mandell LA, Wunderink RG, Anzueto A, Bartlett JG, Campbell GD, Dean NC, Dowell SF, File TM Jr, Musher DM, Niederman MS, Torres A, Whitney CG; Infectious Diseases Society of America; American Thoracic Society. Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults. Clin Infect Dis. 2007 de marzo de 1;44 Suplemento 2:S27-72.

Uyeki TM. Influenza diagnosis and treatment in children: a review of studies on clinically useful tests and antiviral treatment for influenza. Pediatr Infect Dis J. 2003 de febrero de ;22(2):164-77.

Faix DJ, Sherman SS, Waterman SH. Rapid-test sensitivity for novel swine-origin influenza A (H1N1) virus in humans. N Engl J Med. 2009 de agosto de 13;361(7):728-9.

Grijalva CG, Poehling KA, Edwards KM, Weinberg GA, Staat MA, Iwane MK, Schaffner W, Griffin MR. Accuracy and interpretation of rapid influenza tests in children. Pediatrics. Enero de 2007; 119(1):e6-11.

Centros para el Control y la Prevención de Enfermedades (CDC). Evaluación de las pruebas de diagnóstico rápido de la influenza para la detección del nuevo virus de la influenza A (H1N1)—Estados Unidos, 2009. MMWR (Informe semanal de morbilidad y mortalidad) 2009 de agosto de 7;58(30):826-9.

 Arriba

Descargo de responsabilidad: Es posible que en este sitio encuentre algunos enlaces que le lleven a contenido disponible sólo en inglés. Además, el contenido que se ha traducido del inglés se actualiza a menudo, lo cual puede causar la aparición temporal de algunas partes en ese idioma hasta que se termine de traducir (generalmente en 24 horas). Llame al 1-800-CDC-INFO si tiene preguntas sobre la influenza estacional, cuyas respuestas no ha encontrado en este sitio. Agradecemos su paciencia

Guidance for Clinicians on the Use of Rapid Influenza Diagnostic Tests | Health Professionals | Seasonal Influenza (Flu)

Guidance for Clinicians on the Use of Rapid Influenza Diagnostic Tests

On this Page

• Background
• Use of RIDTs in Clinical Decision-making
• Use of RIDTs for Public Health Purposes to Detect Influenza Outbreaks
• Factors Influencing Results of RIDTs
• Interpretation of Rapid Influenza Diagnostic Test Results
• Information on Local Influenza Activity
• When to Consider Further Influenza Testing
• Figure 1
• Figure 2
• Figure 3
• Figure 4
• Table 1
• Table 2
• References

Background

Rapid influenza diagnostic tests (RIDTs) are immunoassays that can identify the presence of influenza A and B viral nucleoprotein antigens in respiratory specimens, and display the result in a qualitative way (positive vs. negative) (1). In the United States, a number of RIDTs are commercially available. (See “Table 1: Influenza Virus Testing Methods” and “Table 2: Characteristics of Rapid Influenza Diagnostic Tests”.) The reference standards for laboratory confirmation of influenza virus infection in respiratory specimens are reverse transcription-polymerase chain reaction (RT-PCR) or viral culture. RIDTs can yield results in a clinically relevant time frame, i.e., approximately 20 minutes or less. However, RIDTs have limited sensitivity to detect influenza virus in respiratory specimens compared to RT-PCR or viral culture and negative RIDT test results should be interpreted with caution given the potential for false negative results, especially during peak influenza activity in a community. Some RIDTs use analyzer reader devices to standardize result interpretation.

1 RIDTs do not include rapid molecular assays. Rapid molecular assays are a new type of influenza diagnostic test that use isothermal nucleic acid amplification for viral detection. At present, only one rapid molecular assay is FDA-approved for use in the United States.

Advantages and Disadvantages of RIDTs

Advantages

• Produce quick result in 15 minutes or less, simple to perform
• Some RIDTs are cleared for office/bedside use. RIDTs that have been CLIA waived can be used in settings that may include point-of-care.

Disadvantages

• Sub-optimal test sensitivity, false negative results are common, especially when influenza activity is high
• Although specificity is high, false positive results can also occur, especially during times when influenza activity is low.
• Some RIDTs distinguish between influenza A or B viruses  while others do not. RIDTs that provide results on type of influenza virus (e.g., influenza A or B virus), do not provide information on influenza A virus subtype [e.g., A(H1N1)pdm09 versus A(H3N2)] or specific virus strain information (e.g., degree of similarity to vaccine strains)

 Top of Page

Use of RIDTs in Clinical Decision-making

RIDTs may be used to help with diagnostic and treatment decisions for patients in clinical settings, such as whether to prescribe antiviral medications. However, due to the limited sensitivities, negative results of RIDTs do not exclude influenza virus infection in patients with signs and symptoms suggestive of influenza. Therefore, antiviral treatment should not be withheld from patients with suspected influenza, even if they test negative by RIDT and further influenza testing of respiratory specimens by molecular assays may be indicated. More information about Antiviral Drugs and recommendations on their use.

Testing is not needed for all patients with signs and symptoms of influenza to make antiviral treatment decisions (See Figures 1-4). Once influenza activity has been documented in the community or geographic area, a clinical diagnosis of influenza can be made for outpatients with signs and symptoms consistent with suspected influenza, especially during periods of peak influenza activity in the community.

 Top of Page

Use of RIDTs for Public Health Purposes to Detect Influenza Outbreaks

RIDTs can be useful to identify influenza virus infection as a cause of respiratory outbreaks in any setting, but especially in institutions (i.e., nursing homes, chronic care facilities, and hospitals), cruise ships, summer camps, schools, etc. Positive RIDT results from one or more ill persons with suspected influenza can support decisions to promptly implement infection prevention and control measures for influenza outbreaks. However, negative RIDT results do not exclude influenza virus infection as a cause of a respiratory outbreak because of the limited sensitivity of these tests. Testing respiratory specimens from several persons with suspected influenza will increase the likelihood of detecting influenza virus infection if influenza virus is the cause of the outbreak. Public health authorities should be notified promptly of any suspected institutional outbreak and respiratory specimens should be collected from ill persons (whether positive or negative by RIDT) and sent to a public health laboratory for more accurate influenza testing by molecular assays and viral culture.

 Top of Page

Factors Influencing Results of RIDTs

Many factors can influence the accuracy of RIDTs, including:

• Clinical signs and symptoms consistent with influenza
  • Having clinical signs and symptoms consistent with influenza increases the pre-test probability of influenza virus infection, which increases the reliability of a positive RIDT result.
• Prevalence of influenza activity in the population tested
  • Influenza activity varies seasonally, which directly affects the predictive values of RIDTs (See algorithms below [Figures 3 and 4], and Prevention Strategies for Seasonal Influenza in Heath Care Settings.)
• Time from illness onset to collection of respiratory specimens for testing
  • Testing specimens collected within 3-4 days of illness onset (when influenza viral shedding is highest) is more likely to yield positive RIDT results if the patient has influenza.
• Type of respiratory specimen tested
  • RIDTs have different specifications for acceptable specimens (e.g., nasopharyngeal, nasal or throat swab/aspirate). The package insert for the RIDT test used should be reviewed to ensure that an appropriate specimen is collected, and test procedures are followed. Some tests may require specimen collection using a special swab (some RIDTs must be used with a swab supplied with the test kit; some swab material can interfere with RIDT results).
  • RIDTs must also ensure that the appropriate viral transport media or other media is used, consistent with test specifications, if testing is done at a different location from where the specimen is collected from the patient.
  • Collection of good quality respiratory specimens (e.g., nasopharyngeal or nasal swab/aspirate/wash or combined nasal/throat swab specimens) also will increase the accuracy of RIDT results.
  • Some RIDTs require that the entire collected specimen be used in the test. Consider whether a second specimen should be collected for confirmatory testing using viral culture and/or RT-PCR.
• Accuracy of the test compared to a reference test (“gold standard” = RT-PCR or viral culture)
  • Sensitivity of the RIDT
    • Proportion of positive RIDT results of all positive “gold standard test” results (RT-PCR or viral culture)
    • Fixed characteristic of a test; generally low to moderate (10-70%) for RIDTs
      • An RIDT with low sensitivity will produce negative results in some patients with influenza (false negatives)
• Specificity of the RIDT
  • Proportion of negative RIDT results of all negative “gold standard test” results (RT-PCR or viral culture)
  • Fixed characteristic of a test; generally very high for RIDTs (90-95%)
    • An RIDT with low sensitivity will produce negative results in some patients with influenza (false negatives)

 Top of Page

Interpretation of Rapid Influenza Diagnostic Test Results

Proper interpretation of RIDT results is very important for clinical management of patients and for assessing suspected influenza outbreaks. The accuracy  of RIDTs depends largely on the conditions under which they are used. Understanding some basic considerations can minimize being misled by false-positive or false-negative results.

• Sensitivities of RIDTs are generally approximately 50-70%, but a range of 10-80% has been reported compared to viral culture or RT-PCR. Specificities of RIDTs are approximately 90-95% (range 85-100%). Thus false negative results occur more commonly than false positive results.
  • Negative results of RIDTs do not exclude influenza virus infection and influenza should still be considered in a patient if clinical suspicion is high based upon history, signs, symptoms and clinical examination.
• A positive result in a person who recently received intranasal administration of live attenuated influenza virus vaccine (LAIV) may indicate detection of vaccine virus. LAIV contains influenza virus strains that undergo viral replication in respiratory tissues of lower temperature (e.g., nasal passages) than internal body temperature. Since the nasal passages are infected with live influenza virus vaccine strains during LAIV administration, sampling the nasal passages within a few days after LAIV vaccination can yield positive influenza testing results. It may be possible to detect LAIV vaccine strains up to 7 days after vaccination, and in rare situations, for longer periods.
• False-positive (and true-negative) results are more likely to occur when disease prevalence in the community is low, which is generally at the beginning and end of the influenza season and during the summer.
  • The negative predictive value of an RIDT (the proportion of patients with negative results who do not have influenza) is highest when influenza activity is low.
  • The positive predictive value of an RIDT (the proportion of patients with positive results who have influenza) is lowest when influenza activity is low.
• False-negative (and true-positive) results are more likely to occur when disease prevalence is high in the community.
  • The positive predictive value of an RIDT (the proportion of patients with positive results who have influenza) is highest when influenza activity is high
  • The negative predictive value of an RIDT (the proportion of patients with negative results who do not have influenza) is lowest when influenza activity is high

Minimize False Results

• Collect specimens as early in the illness as possible (ideally less than 4 days from illness onset).
• Follow manufacturer's instructions, including acceptable specimens, and handling.
• Follow-up negative results with confirmatory tests (RT-PCR or viral culture) if a laboratory-confirmed influenza diagnosis is desired.

 Top of Page 

Clinicians should contact their local or state health department for information about current influenza activity. For more information about influenza activity in the United States during the influenza season, visit the Weekly U.S. Influenza Surveillance Report (FluView).

When to Consider Further Influenza Testing

Consider sending respiratory specimens for influenza testing by viral culture or RT-PCR to confirm results of an RIDT when:

• A patient tests negative by RIDT when community influenza activity is high and laboratory confirmation of influenza is desired.
• A patient tests positive by RIDT and the community prevalence of influenza is low, and a false positive result is a consideration.
• A patient has had recent close exposure to pigs or poultry or other animals and novel influenza A virus infection is possible (e.g., influenza A viruses circulate widely among swine and birds, including poultry, and also can infect other animals such as horses and dogs)

Hospitalized patients

Influenza testing is recommended for hospitalized patients with suspected influenza. Molecular assays such as RT-PCR are recommended for testing hospitalized patients, especially if RIDTs are used and yield negative results. However, empiric antiviral treatment should be initiated as soon as possible for hospitalized patients with suspected influenza without the need to wait for any influenza testing results (see Antiviral Drugs, Information for Health Care Professionals). Antiviral treatment should not be stopped based on negative RIDT results given the limited sensitivities of RIDTs. Infection prevention and control measures should be implemented immediately upon admission for any hospitalized patient with suspected influenza even if RIDT results are negative (see Prevention Strategies for Seasonal Influenza in Heath Care Settings). Respiratory specimens can be tested for influenza by immunofluorescence, RT-PCR or viral culture. Serology for influenza should not be performed for clinical management. Clinicians should understand that negative results of influenza testing do not exclude influenza virus infection, especially if the time from illness onset to collection of respiratory specimens is more than 3  days, or if upper respiratory specimens were tested and the patient has lower respiratory tract disease. If influenza is suspected, testing of clinical specimens collected from different respiratory sites can be done (e.g., upper and lower respiratory tract) and can be collected on more than one day to increase likelihood of influenza virus detection; intubated patients should have endotracheal aspirate specimens tested if influenza is suspected, but not yet confirmed.

Detection of influenza virus infection and prompt implementation of infection prevention and control measures is critical to prevention of nosocomial influenza outbreaks. When there is influenza activity in the community, clinicians should consider influenza testing, including viral culture, for patients who develop signs and symptoms of influenza while they are in a health care facility. This should be done as part of a broader surveillance strategy for influenza as discussed in Prevention Strategies for Seasonal Influenza in Heath Care Settings.

Suspected influenza institutional outbreaks

For suspected influenza outbreaks in institutions, respiratory specimens should be collected from patients with suspected influenza as early as possible once the outbreak is suspected (See Figure 2). The use of influenza molecular assays is preferred. If RIDTs are used in these settings, clinical specimens should also be sent for influenza testing by viral culture and RT-PCR to provide detailed information on specific influenza A virus subtypes and strains, and antiviral susceptibility data and to verify RIDT test results. Active daily surveillance for suspected influenza illness and collection of specimens from patients with suspected influenza should continue through at least 2 weeks after implementation of control measures to assess effectiveness of the measures and to monitor for potential emergence of antiviral resistance. See Prevention Strategies for Seasonal Influenza in Heath Care Settings.

Influenza Surveillance

Laboratory-based surveillance for influenza viruses by viral culture is critically important to the selection of viruses for the next season's influenza vaccine. Virus isolates are needed in order to characterize the circulating influenza A virus subtypes and influenza A and B virus strains and to determine how well they are matched antigenically to vaccine strains. Isolates are also needed for obtaining information on the emergence and prevalence of antiviral resistant strains, and the identification of human infection with novel influenza A virus (e.g., an influenza A virus of animal origin that may sporadically  cause illnesses in people) that may have pandemic potential. This information is needed from specimens sent for viral culture and RT-PCR year round for identification of novel influenza A virus strains or antigenically-drifted  strains, including during times of low influenza activity such as at the beginning and end of influenza seasonal activity. For more information about influenza activity in the United States during the influenza season, visit the Weekly U.S. Influenza Surveillance Report (FluView).

 Top of Page

Figure 1: Guide for considering influenza virus diagnostic tests for individual patients when influenza viruses are circulating in the community1

In Figure 1, start by asking Does the patient have clinical signs and symptoms compatible with influenza?2

If YES, ask Will the results of influenza virus testing*: change clinical care of the patient3 (especially for hospitalized patients and those with high risk conditions4) OR influence clinical practice for other patients?5 *Initiation of antiviral treatment, if clinical indicated, should not be delayed pending results of testing.

If YES, Consider influenza virus testing. (See Table 1 for review of influenza virus testing methods; and Table 2 for review of available RIDTs).

If YES, Interpret influenza test results. (See Figure 3 for RIDTs).

If NO to any, Influenza virus testing probably not indicated.

1. Confirmation of influenza virus infection by diagnostic testing is not required for clinical decisions to prescribe antiviral medications. Decisions to administer antiviral medications for influenza treatment or chemoprophylaxis, if indicated, should be based upon clinical illness and epidemiologic factors, and start of antiviral therapy should not be delayed pending testing results. Respiratory specimens should be collected from an ill patient as early as possible after onset of symptoms (ideally <48-72 hours after onset) to help maximize influenza testing sensitivity.
2. Influenza like-illness (history of feverishness or documented fever with either cough or sore throat), fever with other respiratory symptoms, etc. Note that some persons may have atypical presentations (e.g., elderly, very young infants, immunosuppressed, and patients with certain chronic medical conditions). Fever is not always present (e.g., premature infants, young infants, elderly, immunosuppressed). Other symptoms associated with influenza include myalgias, headache, fatigue. Complications include exacerbation of underlying chronic disease, (e.g., congestive cardiac failure, asthma), pneumonia, bacterial co-infection, bronchiolitis, croup, encephalopathy, encephalitis, seizures, myositis, and others.
3. e.g., Decisions on use of antibiotics or antiviral medications, on conducting further diagnostic tests, on recommendations for home care, or on recommendations for ill persons living with persons with high-risk conditions. Consult IDSA, ATS, AAP antibiotic guidance.
4. Persons aged >65 years or <2 years; pregnant women; persons with chronic lung disease (including asthma), heart disease, renal, metabolic, hematologic and neurologic disease; immunosuppression; and morbid obesity.
5. e.g., Decisions on changing infection prevention and control practices (such as in hospitalized patients); if a positive influenza test result is used for confirming influenza virus circulation in the community which might inform clinical practices related to home care guidance, hospital infection control practices, future testing practices, etc.

 Top of Page

Figure 2: Guide to use of influenza virus diagnostic tests in investigating outbreaks in institutional or other closed settings1

In Figure 2, start by asking: “Are there 2 or more persons with onset within 2-3 days of each other2 currently with clinical signs and symptoms compatible with influenza virus infection?”3

If YES, ask Will the results of influenza virus testing change outbreak control strategies in the population?4 OR Does the setting include persons at high risk of influenza complications should they become infected (e.g., LTCFs)?5

If YES, Consider influenza virus testing. (See Table 1 for review of influenza virus testing methods; and Table 2 for review of available RIDTs).

If YES, Interpret influenza test results. (See Figure 3 for RIDTs).

If NO to any, Influenza virus testing probably not indicated.

1. Examples of institutional or closed settings include long-term care facilities, nursing homes, schools, correctional facilities, hospitals, ships.
2. In settings where persons at high-risk of influenza complications reside, a single case of suspected influenza is sufficient for triggering influenza testing and consideration of implementation of empiric infection prevention and control measures, including active surveillance for new illness cases.
3. e.g., Influenza like-illness (fever with either cough or sore throat), fever with other respiratory symptoms, etc. Note that some persons may have atypical presentations (e.g., elderly, very young infants, immunosuppressed, and patients with certain chronic medical conditions). Fever is not always present. Other symptoms associated with influenza include myalgias, headache, fatigue. Complications include exacerbation of underlying chronic disease, (e.g., congestive cardiac failure, asthma), pneumonia, bacterial co-infection, bronchiolitis, croup, encephalopathy, encephalitis, seizures, myositis, and others.
4. e.g., use of antivirals empirically for treatment or for chemoprophylaxis of influenza, changes in infection prevention and control practices (isolation or cohorting of ill, quarantine of exposed), changes in admission or staffing policies, or changes in social distancing recommendations, etc.
5. Persons aged >65 years or <2 years; pregnant women; persons with chronic lung disease (including asthma), heart disease, renal, metabolic, hematologic and neurologic disease; immunosuppression; and morbid obesity.
6. In an outbreak setting, RT-PCR or other molecular assays are preferred. Because of the low sensitivity of RIDTs, use of the tests on specimens from more than one ill person is recommended. The presence of any influenza positives among persons with clinically compatible illnesses is supportive of influenza as the probable cause of the outbreak. Negative RIDT results do not exclude influenza virus infection. Confirmation of RIDT results by more RT-PCR  or viral culture specific influenza testing is indicated.

 Top of Page

Figure 3: Algorithm to assist in the interpretation of RIDT results and clinical decision-making during periods when influenza viruses are circulating in the community1

In Figure 3, if the RIDT is POSITIVE for one of the following: Influenza A, Influenza B, or Influenza A and B (A/B) then the interpretation is Influenza virus infection likely.1,2 Actions are to initiate antiviral treatment for influenza if clinically indicated. Consider additional influenza virus testing to confirm RIDT results, for subtyping of influenza A virus, to distinguish between influenza A and B viruses, or for more specific analyses, if indicated. Consider additional diagnostic testing for other pathogens and/or empiric antibiotic therapy for bacterial co-infection, in indicated3.

In Figure 3, if the RIDT is NEGATIVE for one or more of the following: Influenza A, Influenza B, or Influenza A and B (A/B) then the interpretation is Cannot rule out Influenza virus infection.1,2 Actions are to use clinical signs, symptoms, history, examination, information on local influenza activity in the community to decide if antiviral treatment is indicated. Do not use negative RIDT results exclusively for clinical decision-making, or for public health decisions, including identifying influenza outbreaks, or for decisions on infection control measures. Consider additional diagnostic testing for other pathogens and/or empiric antibiotic therapy for bacterial co-infection, in indicated3.

1. During periods when influenza activity is high and influenza viruses are circulating among persons in the community (see 3. below), the positive predictive value of a test result is high (that is, the chance that a positive result indicates that the patient has influenza is high), and the negative predictive value of a test result is low (the chance that a negative result is a true negative is low) due to low sensitivity of RIDTs to detect influenza virus in respiratory specimens compared to RT-PCR or viral culture: false negative results are common.
2. Influenza virus infection may include seasonal influenza A (H3N2), A(H1N1)pdm09, influenza B, or rarely, a novel influenza A virus infection. The interpretation of RIDTs will, in part, depend on the test used – some will detect influenza A, some will detect influenza B and some will detect both A and B viruses. If tests for both influenza A and influenza B are positive, refer specimen to a public health laboratory for resolution, as dual infections are uncommon.
3. Consult local or state health departments or other sources (e.g., virology testing at a local hospital) for local activity on other respiratory pathogens associated with acute respiratory illness. Empiric antibiotic coverage should include coverage for Streptococcus pneumoniae, Staphylococcus aureus (including MRSA), Group AStreptococcus, and others, especially for hospitalized adult patients per IDSA/ATS CAP guidelines.

 Top of Page

Figure 4: Algorithm to assist in the interpretation of RIDT results and clinical decision-making during periods when influenza viruses are not circulating or influenza activity is low in the community1

In Figure 4, if the RIDT is POSITIVE for one of the following: Influenza A, Influenza B, or Influenza A and B (A/B) then the interpretation is Cannot exclude false positive result.1,2 Actions are to use clinical signs, symptoms, history, examination, information on local influenza activity in the community to decide if antiviral treatment is indicated. Additional influenza virus testing by RT-PCR or other molecular assays is recommended to confirm RIDT results, for subtyping of influenza A virus, to distinguish between influenza A and B viruses, or for more specific analyses, if indicated. Consider additional diagnostic testing for other pathogens and/or empiric antibiotic therapy for bacterial co-infection, in indicated3.

In Figure 4, if the RIDT is NEGATIVE for one or more of the following: Influenza A, Influenza B, or Influenza A and B (A/B) then the interpretation is Cannot rule out Influenza virus infection.1,2 Actions are to use clinical signs, symptoms, history, examination, information on local influenza activity in the community to decide if antiviral treatment is indicated. Do not use negative RIDT results exclusively for clinical decision-making, or for public health decisions, including identifying influenza outbreaks, or for decisions on infection control measures. Consider additional diagnostic testing for other pathogens and/or empiric antibiotic therapy for bacterial co-infection, in indicated3.

1. During periods when influenza activity is low and there is low influenza virus circulation among persons in the community, the positive predictive value of a rapid influenza diagnostic test is low (that is, the chance that a positive result indicates that the patient has influenza is low), and the negative predictive value is high (the chance that a negative result is a true negative is high). Even though RIDTs have high specificity, false positive RIDT results are more common when influenza activity is low.
2. Influenza virus infection may include seasonal influenza A (H3N2), A(H1N1)pdm09, influenza B, or rarely, a novel influenza A virus infection. The interpretation of RIDTs will, in part, depend on the test used – some will detect influenza A, some will detect influenza B and some will detect both A and B viruses. If tests for both influenza A and influenza B are positive, refer specimen to a public health laboratory for resolution, as dual infections are uncommon.
3. Consult local or state health departments or other sources (e.g., virology testing at a local hospital) for local activity on other respiratory pathogens associated with acute respiratory illness. Empiric antibiotic coverage should include coverage for Streptococcus pneumoniae, Staphylococcus aureus (including MRSA), Group AStreptococcus, and others, especially for hospitalized adult patients per IDSA/ATS CAP guidelines.

 Top of Page

Table 1: Influenza Virus Testing Methods

Method1	Types Detected	Acceptable Specimens2	Test Time	CLIA Waived3
Viral cell culture (conventional)	A and B	NP4 swab, throat swab, NP2 or bronchial wash, nasal or endotracheal aspirate, sputum	3-10 days	No
Rapid cell culture (shell vials; cell mixtures)	A and B	As above	1-3 days	No
Immunofluorescence, Direct (DFA) or Indirect (IFA) Antibody Staining [antigen detection]	A and B	NP4 swab or wash, bronchial wash, nasal or endotracheal aspirate	1-4 hours	No
RT-PCR5 (singleplex and multiplex; real-time and other RNA-based) and other molecular assays	A and B	NP4 swab, throat swab, NP2 or bronchial wash, nasal or endotracheal aspirate, sputum	Varied (Generally ≤15 minutes-6 hours)7	No
Rapid Molecular Assay	A and B	NP4 swab, nasal aspirate, wash, swab	≤15 minutes7	Yes/No7
Rapid Influenza Diagnostic Tests6 (antigen detection)	A and B	NP4 swab, (throat swab), nasal wash, nasal aspirate	<30 min.	Yes/No

1. Serologic (antibody detection) testing is not recommended for routine patient diagnosis.
2. Ref: Leland, et al. 2007, Clin Micro Rev 20: 49-78. Approved respiratory specimens vary among FDA cleared influenza assays.
3. Ref: http://www.cms.gov/Regulations-and-Guidance/Legislation/CLIA/index.html
4. NP = nasopharyngeal
5. Reverse transcriptase polymerase chain reaction, including FDA-approved test systems, reference laboratory testing using ASR or lab-developed reagents
6. Chromatographic- and/or fluorescence-based lateral flow and membrane-based immunoassays
7. Rapid molecular assays can provide results in 15 minutes or less.  Alere i Influenza A&B was cleared by FDA for nasal swabs and viral transport media.  Alere i Influenza A&B was CLIA-waived only for use with nasal swabs.

 Top of Page

Table 2: Characteristics of Rapid Influenza Diagnostic Tests1

Procedure (Manufacturer/Distributor)	Influenza Virus Types Detected	Approved Specimens2	CLIA Waived3	Uses Analyzer Reader Device
Alere™ i Influenza A/B (Alere Scarborough, Inc.)	A and B	Nasal swab (in VTM8)	No	Yes
Alere™ i Influenza A/B4 (CLIA Waived) (Alere Scarborough, Inc.)	A and B	Nasal swab (Direct)	Yes	Yes
BD Directigen™ EZ Flu A+B4 (Becton-Dickinson & Co.)	A and B	NP5 wash/aspirate/swab Throat swab	No	No
BD Veritor™ System for Rapid Detection of Flu A+B4 (CLIA-waived), (Becton Dickinson & Co.)	A and B	NP5 swab/ nasal swab	Yes	Yes
BD Veritor™ System for Rapid Detection of Flu A+B4 (Moderately Complex), (Becton Dickinson & Co.)	A and B	NP5 wash/aspirate	No	Yes
Binax NOW® Influenza A&B4 Test (Binax, Inc.)	A and B	NP5 swab, Nasal wash/aspirate/swab	Yes	No
BioSign® Flu A+B4 or OraSure QuickFlu Rapid A+B Test or Polymedco Poly stat Flu A&B Test or LifeSign LLC Status Flu A&B (Princeton BioMedtech Corp.)	A and B	NP5 swab/aspirate/wash, nasal swab	No	No
ClearView Exact II Influenza A&B Test or Alere Influenza A&B Test (Binax d/b/a Inverness Medical Alere Scarborough, Inc.)	A and B	Nasal swab	Yes	No
Genzyme OSOM® Influenza A&B4 Test (Genzyme Corp.)	A and B	Nasal swab	No	No
QuickVue® Influenza A/B Test6 (Quidel Corp.)	A and B	Nasal wash/aspirate/swab	Yes	No
QuickVue® Influenza A+B Test4 (Quidel Corp.)	A and B	NP5 swab Nasal wash/aspirate/swab	Yes	No
RAMP Influenza A/B Assay or 3M™ Rapid Detection Flu A+B Test4 (Response Biomedical Corp.)	A and B	NP5 swab/aspirate Nasal wash/aspirate	No	Yes
SAS™ FluAlert A&B Test (SA Scientific, Inc.)	A and B	Nasal wash/aspirate	No	No
SAS™ Influenza A4 Test (SA Scientific, Inc.)	A only	Nasal wash/aspirate	Yes	No
SAS™ Influenza B6 Test (SA Scientific, Inc.)	B only	Nasal wash/aspirate	Yes	No
Sofia® Analyzer and Influenza A+B FIA (CLIA-waived) (Quidel Corp.)	A and B	NP5 swab Nasal swab	Yes	Yes
Sofia® Analyzer and Influenza A+B4,7, FIA (Quidel Corp.)	A and B	NP5 aspirate/swab/wash Nasal swab	No	Yes
TRU FLU®4 (Meridian Bioscience, Inc.)	A and B	NP5 aspirate/swab Nasal wash/swab	No	No
XPECT™ Influenza A/B4 (Remel Inc./Thermo Fisher Scientific)	A and B	Nasal wash/swab Throat swab	No	No

Print-friendly Version PDF[218 KB, 3 pages]

 Top of Page

1. List may not include all test kits approved by the U.S. Food and Drug Administration. Discontinued tests not included.
2. Approved respiratory specimens according to manufacturer's package insert. Note that test performance may vary if other respiratory specimens are used.
3. Ref: http://www.cms.gov/Regulations-and-Guidance/Legislation/CLIA/index.html
4. Distinguishes between influenza A and B virus infections.
5. NP = nasopharyngeal.
6. Does not distinguish between influenza A and B virus infections when used alone.
7. Requires use of a separate analyzer reader device.
8. VTM = viral transport media

Disclaimer: Use of trade names or commercial sources is for identification only and does not imply endorsement by the Centers for Disease Control and Prevention or the Department of Health and Human Services.

References

Ali T, Scott N, Kallas W, Halliwell ME, Savino C, Rosenberg E, Ferraro M, Hohmann E. Detection of influenza antigen with rapid antibody-based tests after intranasal influenza vaccination (FluMist). Clin Infect Dis. 2004 Mar 1;38(5):760-2.

Balish A, Garten R, Klimov A, Villanueva J. Analytical detection of influenza A(H3N2)v and other A variant viruses from the USA by rapid influenza diagnostic tests. Influenza Other Respi Viruses. 2012 Sep 18. doi: 10.1111/irv.12017. [Epub ahead of print]

Bell J, Bonner A, Cohen DM, Birkhahn R, Yogev R, Triner W, Cohen J, Palavecino E, Selva-rangan R. Multicenter clinical evaluation of the novel Alere™ i Influenza A&amp;B isothermal nucleic acid amplification test. J Clin Virol. 2014 Sep;61(1):81-6.

Block SL, Yogev R, Hayden FG, Ambrose CS, Zeng W, Walker RE. Shedding and immunogenicity of live attenuated influenza vaccine virus in subjects 5-49 years of age. Vaccine. 2008 Sep 8;26(38):4940-6.

Centers for Disease Control and Prevention (CDC). Evaluation of rapid influenza diagnostic tests for influenza A (H3N2)v virus and updated case count--United States, 2012. MMWR Morb Mortal Wkly Rep. 2012 Aug 17;61(32):619-21.

Centers for Disease Control and Prevention (CDC). Evaluation of 11 commercially available rapid influenza diagnostic tests - United States, 2011-2012. MMWR Morb Mortal Wkly Rep. 2012 Nov 2;61:873-6.

Chartrand C, Leeflang MM, Minion J, Brewer T, Pai M. Accuracy of rapid influenza diagnostic tests: a meta-analysis. Ann Intern Med. 2012 Apr 3;156(7):500-11.

Committee on Infectious Diseases, American Academy of Pediatrics. Policy Statement—Recommendations for Prevention and Control of Influenza in Children, 2010–2011.

Harper SA, Bradley JS, Englund JA, File TM, Gravenstein S, Hayden FG et al. Seasonal influenza in adults and children—diagnosis, treatment, chemoprophylaxis, and institutional outbreak management: clinical practice guidelines of the Infectious Diseases Society of America. Clin Infect Dis.2009 Apr 15;48(8):1003-32.

Hazelton B, Gray T, Ho J, Ratnamohan VM, Dwyer DE, Kok J. Detection of influenza A and B with the Alere i Influenza A & B: a novel isothermal nucleic acid amplification assay. Influenza and Other Respiratory Viruses 2015;9(3):151-4.

World Health Organization. WHO Guidelines for Pharmacological Management of Pandemic Influenza A(H1N1) 2009 and other Influenza Viruses. Revised February 2010[540 KB, 32 pages].

Mandell LA, Wunderink RG, Anzueto A, Bartlett JG, Campbell GD, Dean NC, Dowell SF, File TM Jr, Musher DM, Niederman MS, Torres A, Whitney CG; Infectious Diseases Society of America; American Thoracic Society. Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults. Clin Infect Dis. 2007 Mar 1;44 Suppl 2:S27-72.

Uyeki TM. Influenza diagnosis and treatment in children: a review of studies on clinically useful tests and antiviral treatment for influenza. Pediatr Infect Dis J. 2003 Feb;22(2):164-77.

Faix DJ, Sherman SS, Waterman SH. Rapid-test sensitivity for novel swine-origin influenza A (H1N1) virus in humans. N Engl J Med. 2009 Aug 13;361(7):728-9.

Grijalva CG, Poehling KA, Edwards KM, Weinberg GA, Staat MA, Iwane MK, Schaffner W, Griffin MR. Accuracy and interpretation of rapid influenza tests in children. Pediatrics. 2007 Jan;119(1):e6-11.

Centers for Disease Control and Prevention (CDC). Evaluation of rapid influenza diagnostic tests for detection of novel influenza A (H1N1) Virus—United States, 2009. MMWR Morb Mortal Wkly Rep. 2009 Aug 7;58(30):826-9.