More than half of patients hospitalized with suspected COVID-19 in Michigan during the state’s peak months received antibiotics early in their stay, just in case they had a bacterial infection in addition to the virus, a new study shows. But testing soon showed that 96.5% of them only had the coronavirus, which antibiotics don’t affect.

The 3.5% of patients who arrived at the hospital with both kinds of infection were more likely to die. But the study suggests that faster testing and understanding of infection risk factors could help hospital teams figure out who those patients are – and spare the rest of their COVID-19 patients the risks that come with the overuse of antibiotics.