Seroprevalence of antibodies to SARS‐CoV‐2 in healthcare workers in a nonepidemic region, Japan: A hospital‐based study on May, 2020

The polymerase chain reaction (PCR) testing rate is low in our local area and the true rate of coronavirus disease 2019 (COVID‐19) infection may include many asymptomatic individuals. We conducted a serosurveillance using antibody testing in an area where official report of COVID‐19 infection is not done yet. Blood samples were obtained from 1404 healthcare workers (41 ± 11 years) in our hospital on May 29–31, 2020. First, the potential infection frequency was confirmed using two quantitative antibody tests. In addition, the usefulness of rapid antibody kit testing for COVID‐19 serosurveillance was examined. A COVID‐19‐indected case was defined as showing positive results in both quantitative tests. None of 1404 samples had positive results from the two quantitative tests. The false positive rates were 0.36% and 0.07%, whereas those in rapid antibody kits were 3.3% and 3.0%. In conclusion, as of May, 2020, potential spread mainly by asymptomatic individuals infected with COVID‐19 was not found in our local area where there was no official report of COVID‐19, even if the PCR testing rate was low. Rapid antibody kits might not be useful due to the high false positive rate in an area with a low incidence of COVID‐19 infected individuals.