I practice at a tertiary care center where we see the most complicated cases of influenza, such as a previously healthy 5-year-old with influenza who now requires a ventilator for necrotizing pneumonia or a 10-year-old with influenza and meningoencephalitis who may have long-term sequelae if they survive. So, from my perspective, it has always been good medical practice to test and treat patients according to current CDC recommendations. The CDC states that influenza virus testing can inform clinical management when the results may influence clinical decisions (eg, whether to initiate antiviral treatment, whether to perform other diagnostic testing, whether to implement infection prevention and control measures for influenza). Patients who are admitted to the hospital with influenza, those with severe and/or progressing disease, and those who are at risk for complications of influenza due to underlying medical conditions or young age should be tested and treated appropriately. The CDC also notes that confirmation of influenza virus infection by diagnostic testing is not required for clinical decisions regarding the prescription of antiviral medications.

It is vitally important, however, for the interpretation of results to be informed by influenza activity in the community and by the limitations of the test being utilized. Indeed, providers should be very familiar with the sensitivity and specificity of the various influenza tests. Generally, antigen detection tests for influenza are not very sensitive, and molecular detection tests are often preferred. Tests might not distinguish between influenza A virus subtypes or between seasonal influenza A viruses and novel influenza A viruses. Novel strains that differ significantly from those expected may not, in fact, be detected by routine testing. For example, many cases from the 2009 pandemic were influenza A (H1N1), but rapid test results came back negative because of low sensitivity for that strain. In general, antigen detection tests (eg, rapid influenza diagnostic tests, immunofluorescence assays) have suboptimal sensitivities to detect influenza viruses in respiratory specimens compared with molecular assays and viral culture. Negative results of antigen detection tests should therefore not be used to exclude a diagnosis of influenza. The CDC publishes an algorithm to assist with the interpretation of influenza testing results and clinical decision making during periods when the influenza virus is circulating in the community. This also underscores the importance of paying attention to influenza surveillance in a given community. Guidelines and recommendations regarding infectious diseases are subject to change as conditions in the community change, so it is always a good idea to check for updates.