A high proportion of COVID-19 infections among front line hospital workers appear to go undetected, with one in 20 showing antibody evidence, US data shows. 

Between April and June, more than 3200 (6%) front line healthcare workers in 12 states were found to have antibody evidence of previous SARS-CoV-2 infection.

But 69% of those infections had never been diagnosed, according to study in the Morbidity and Mortality Weekly Report of the US Centers for Disease Control and Prevention.

Among healthcare workers with antibodies, about one third did not recall having symptoms in the preceding months, the data showed.