clinical topic updates
Recommendations for Respiratory Virus Testing for Influenza
Influenza testing is not routinely recommended for all outpatients with signs and symptoms of influenza during a seasonal outbreak. However, patients admitted to the hospital and certain others suspected of having influenza should be tested. Our featured expert discusses the current thinking on and recommendations for respiratory virus testing for influenza.
Associate Professor of Pediatrics and Infectious Diseases
“Providers should be very familiar with the specificity and sensitivity of the various influenza tests.”
The question of whether to perform respiratory virus testing on outpatients with suspected influenza is a topic with different schools of thought. Some clinicians simply do not routinely test for or treat influenza, while others will only treat the most severely ill patients. I practice at a tertiary care center where we see the most complicated cases of influenza, such as a previously healthy 5-year-old patient with influenza who now requires a ventilator for necrotizing pneumonia and a 10-year-old patient with influenza and meningoencephalitis who may have long-term sequelae if they survive. In my opinion, it is good medical practice for physicians to test and treat their patients according to current Centers for Disease Control and Prevention (CDC) recommendations. 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. Physicians should not wait for test results to begin treatment for patients with suspected influenza whom they believe should be treated.
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 specificity and sensitivity of the various influenza tests. Antigen detection tests are not very sensitive, and molecular detection tests are now 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, although many cases from the 2009 pandemic looked like influenza, test results came back negative. 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.
Centers for Disease Control and Prevention. Algorithm to assist in the interpretation of influenza testing results and clinical decision-making during periods when influenza viruses are circulating in the community. https://www.cdc.gov/flu/professionals/diagnosis/algorithm-results-circulating.htm. Accessed February 13, 2019.
Centers for Disease Control and Prevention. Overview of influenza testing methods.
https://www.cdc.gov/flu/professionals/diagnosis/overview-testing-methods.htm. Accessed February 13, 2019.
Merckx J, Wali R, Schiller I, et al. Diagnostic accuracy of novel and traditional rapid tests for influenza infection compared with reverse transcriptase polymerase chain reaction: a systematic review and meta-analysis. Ann Intern Med. 2017;167(6):394-409.