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Diagnosis H1N1
Clinicians should suspect novel influenza A virus if an acute febrile respiratory illness or sepsis-like syndrome is presented. But, not all people with suspected novel influenza (H1N1) infection need to have the diagnosis confirmed, especially, if the person resides in an affected area even if the illness is mild.
Indications for investigation are- if the persons
- Require hospitalization or
- Are at high-risk for severe disease.
Tests: Upper respiratory specimens should be collected for testing H1N1 which includes nasopharyngeal swab or aspirate, nasal swab plus a throat swab or nasal wash, or tracheal aspirate.
A trained physician / microbiologist preferably should collect the sample before anti-viral treatment. The specimens should be kept in a refrigerator (not a freezer) at 4°C in viral transport media until testing. The samples should be transported within 24 hours for testing. If transportation cannot be done within time, it should be stored at -70°C. Paired blood samples should also be collected at an interval of 14 days for serological testing. Confirmation of influenza A (H1N1) infection is done by:
- Real time RT PCR or
- Isolation of the virus in culture or
- Four-fold rise in virus specific neutralizing antibodies. 16
Respiratory Viral Panel (RVP) test can detect 20 different virus types and subtypes with the use of multiplex RT-PCR in a single test and with a micro fluidic array on the Luminex 100. Hence, this is used for detecting swine flu in cases with Influenza Like Illness (ILI) due to lack of specific tests for diagnosing H1N1. 14
A confirmed case of novel influenza A (H1N1) virus infection is defined as a person with an influenza-like illness with laboratory confirmed novel influenza A (H1N1) virus infection by real-time RT-PCR or viral culture.
A probable case of novel influenza A (H1N1) virus infection is defined as a person with influenza-like-illness who is positive for influenza A, but negative for human H1 and H3 by influenza RT_PCR.
A suspected case of novel influenza A (H1N1) virus infection is defined as a person who does not meet the confirmed or probable case definition, and is not novel H1N1 test negative, and is/has:
- a previously healthy person < 65 years hospitalized for influenza like illness OR
- influenza like illness and resides in a state without confirmed cases, but has traveled to a state or country where there are one or more confirmed or probable cases OR
- Influenza like illness and has an epidemiologic link in the past 7 days to a confirmed case or probable case. 16
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