This past week our topic was the Laboratory Methods in Basic Virology. Influenza virus, especially the H1N1 strand, has caused an epidemic worldwide during the last few years. I will be discussing in this thread the CDC guidance for processing of influenza testing in the clinical laboratory.
At this time, there are only two FDA approved assays for confirmation of novel influenza A(H1N1) virus infection, including the CDC rRT-PCR Swine Flu Panel assay. Confirmation of influenza A(H1N1) infection may be necessary for surveillance purposes and for special situations, such as immunocompromised patients or in pregnancy.
Compared to RT-PCR, the sensitivity of RIDTs for detecting novel influenza A (H1N1) virus infections ranged from 10-70%. Therefore, a negative RIDT result does not rule out novel influenza A (H1N1) virus infection. The type of respiratory specimen (i.e., nasal vs. nasopharyngeal swab), quality of the specimen, time from illness onset to specimen collection, the age of the patient, time from specimen collection to testing, and the storage and processing of the specimen prior to testing, all are factors that contribute to the sensitivity of these tests.
Positive test result with RIDT indicates that the influenza virus infection is likely present in the specimen. A negative rapid test result does not rule out influenza virus infection, and clinical presentation should always be taken into consideration.
The specificity of RIDTs is generally high. However, especially during periods of low influenza activity (e.g. the very beginning of the season), however false positive results can occur.
The CDC recommends adding a statement when about the test limitations in the report of results so that the physician can decide how best to use the test for patient management.
"Example of a Statement to Accompany Rapid Influenza Diagnostic Test Results
Many different laboratory diagnostic tests can be used for detecting the presence of influenza viruses in respiratory specimens. These tests include direct antigen detection tests, virus isolation in cell culture, or detection of influenza-specific RNA by rRT-PCR methods.
At this time, there are only two FDA approved assays for confirmation of novel influenza A(H1N1) virus infection, including the CDC rRT-PCR Swine Flu Panel assay. Confirmation of influenza A(H1N1) infection may be necessary for surveillance purposes and for special situations, such as immunocompromised patients or in pregnancy.
Rapid influenza diagnostic tests (RIDTs) are antigen detection tests that detect the influenza viral nucleoprotein antigen, and these assays are point of care tests. Some of these tests, with high sensitivity and specificity, can detect and distinguish between influenza A and B viruses, but none can distinguish between the different subtypes. The sensitivities of RIDTs to detect influenza B viruses are lower than for detection of influenza A viruses. The sensitivities of RIDTs appear to be higher for specimens collected from children than specimens collected from adults.
Compared to RT-PCR, the sensitivity of RIDTs for detecting novel influenza A (H1N1) virus infections ranged from 10-70%. Therefore, a negative RIDT result does not rule out novel influenza A (H1N1) virus infection. The type of respiratory specimen (i.e., nasal vs. nasopharyngeal swab), quality of the specimen, time from illness onset to specimen collection, the age of the patient, time from specimen collection to testing, and the storage and processing of the specimen prior to testing, all are factors that contribute to the sensitivity of these tests.
Positive test result with RIDT indicates that the influenza virus infection is likely present in the specimen. A negative rapid test result does not rule out influenza virus infection, and clinical presentation should always be taken into consideration.
The specificity of RIDTs is generally high. However, especially during periods of low influenza activity (e.g. the very beginning of the season), however false positive results can occur.
The CDC recommends adding a statement when about the test limitations in the report of results so that the physician can decide how best to use the test for patient management.
"Example of a Statement to Accompany Rapid Influenza Diagnostic Test Results
RIDT result: Positive for Influenza Type A
Note: This test can not distinguish influenza A virus subtypes. For example, this test cannot distinguish influenza infections caused by novel influenza A viruses versus seasonal influenza A viruses.
RIDT result: Negative for Influenza A and B
Note: The sensitivity of this assay has been shown to range between [10-70%*] for the detection of novel influenza A (H1N1) virus and between [20-100%*] for seasonal influenza viruses. A negative result does not exclude influenza virus infection. If influenza is circulating in your community, a diagnosis of influenza should be considered based on a patient’s clinical presentation and empiric antiviral treatment should be considered, if indicated. If more conclusive testing is desired, follow-up confirmatory testing with either [viral culture or RT-PCR*] is warranted".
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| http://www.cdc.gov/h1n1flu/guidance/rapid_testing.htm |
Your post is very informative feel that I benefited from reading it. I just wanted to add that I actually contracted H1N1 in spring of 2010. I found my diagnosis really strange since my symptoms were so mild. My symptoms that lead me into the doctors office was a congested cough that had been going on for two weeks and a runny nose.
ReplyDeleteCassie Marotta