polymerase chain reaction (RT-PCR), and immunofluorescence
assays (90). Serologic testing requires paired acute and convalescent
sera, is not widely available, and is not recommended except for
epidemiologic investigations and research. As with any diagnostic
test, influenza test results should be evaluated in the context of other
clinical and epidemiologic information available to health-care providers.
Sensitivity and specificity of any test for influenza, including
those that detect 2009 H1N1 virus, can vary by the laboratory that
performs the test, the type of test used, the type of specimen tested,
the quality of the specimen, and the timing of specimen collection
in relation to illness onset. Among respiratory specimens for viral
isolation or rapid detection of influenza viruses, nasopharyngeal
and nasal specimens generally have higher yields than throat swab
specimens (91). In addition, positive influenza tests that yield vaccine
virus strains have been reported up to 7 days after receipt of live
attenuated influenza virus vaccine (92).
Commercial rapid influenza diagnostic tests (RIDTs) are available
that can detect influenza virus antigens within 15 minutes
of testing (93,94). Certain tests are cleared by the Food and Drug
Administration (FDA) for use in any outpatient setting whereas others
must be used in a moderately complex clinical laboratory. These
RIDTs differ by whether they can distinguish between influenza
virus types. Available tests can either 1) detect influenza A and B
viruses but not distinguish between the two types or 2) detect both
influenza A and B viruses and also distinguish between the two types.
None of the rapid influenza diagnostic tests specifically identifies any
influenza A virus subtypes.
The types of specimens acceptable for use (i.e.,