CDC publishes guidance on testing for flu, COVID-19, RSV

The CDC recently updated its online guidance about viral testing of patients with acute respiratory illness.

The guidance, which applies when influenza and COVID-19 are both circulating, is categorized by health care setting and was updated on the CDC website on Dec. 6.

For patients who are being hospitalized, the CDC recommends implementing infection prevention and control measures and collecting respiratory specimens for influenza and SARS-CoV-2 testing. Ideally, patients should be tested with the multiplex nucleic acid detection assay for influenza A/B/SARS-CoV-2. If not possible, tests can be conducted separately. Negative SARS-CoV-2 results on antigen testing should be confirmed by a SARS-CoV-2 nucleic acid detection assay or repeat antigen testing 48 hours later. If the second antigen test is negative, a third antigen test could be considered if there is a high clinical suspicion of COVID-19. Rapid influenza antigen detection assays are not recommended due to their lower sensitivities.

Testing for respiratory syncytial virus (RSV) should be considered in certain high-risk patients (e.g., infants, patients with congenital cardiac disease, chronic lung disease, immunocompromised, elderly). In patients on mechanical ventilation with suspected COVID-19 or flu but no confirmed diagnosis, lower respiratory tract (e.g., endotracheal aspirate) specimens should be collected for SARS-CoV-2 and influenza virus testing by nucleic acid detection assay.

In the outpatient or ED setting, the recommendations for testing patients who are expected to be hospitalized are the same. For patients who likely don't require hospitalization, the most significant difference deals with flu testing. The guidance recommends a rapid influenza nucleic acid detection assay if the results will change clinical management or infection control decisions (e.g. long-term care facility resident returning to a facility, or a person of any age returning to a congregate setting).

The guidance also reviews treatment for inpatients, calling for supportive care and treatment for suspected or confirmed COVID-19 per NIH guidelines. If flu is suspected, empiric oseltamivir treatment should be started without waiting for test results, per Infectious Diseases Society of America (IDSA) guidelines. If bacterial pneumonia or sepsis is suspected, clinicians should also follow the relevant IDSA guidelines, the update said. Finally, any appropriate vaccinations should be offered or recommended at discharge.