About 1 in 5 people with COVID-19 are also infected with other respiratory viruses, according to a preliminary analysis.

The authors from Stanford School of Medicine say their findings challenge the assumption that if a patient tests positive for a different respiratory virus, they don’t have COVID-19.

“In some cases, a patient with respiratory symptoms may first be tested for a non-COVID virus. If there is a diagnosis of influenza or rhinovirus, or other respiratory virus, a hospital may discharge the patient without COVID testing, concluding that the alternative diagnosis is the reason for the symptoms,” lead author and Professor of Emergency Medicine Ian Brown said. 

The research team performed 562 SARS-COV-2 tests in their emergency department, 181 were also tested for Flu A/B/RSV and 336 tested with RESPCR2 panel.

Of the 562 patients, 127 (22.6%) were positive for other viruses. (The researchers noted that this figure would be 24.5% if they used 181+336 = 517 as denominator).

Of the 49 positive SARS-COV-2 results, 11 (22.4%) also had a co-infection. Of the 127 positive for other viruses, 11 (8.66%) had a SARS-COV-2 co-infection

The researchers published their findings on Medium.com at the request of the California Department of Public Health.