Four in 10 health care workers who test positive for COVID-19 don't have symptoms, which means they could unknowingly spread the disease to co-workers and patients, researchers say. For the new study, the research team reviewed 97 studies that included more than 230,000 health care workers in 24 countries. Rates of SARS-CoV-2 infection among the health care workers ranged from 7% to 10%. Of those who tested positive for the virus, 48% were nurses, 25% were doctors and 23% were other health care workers.