Prospective observational study and serosurvey of SARS-CoV-2 infection in asymptomatic healthcare workers at a Canadian tertiary care center

Ferreira, Victor H.; Chruscinski, Andrzej; Kulasingam, Vathany; Pugh, Trevor J.; Dus, Tamara; Wouters, Brad; Oza, Amit; Ierullo, Matthew; Ku, Terrance; Majchrzak-Kita, Beata; Humar, Sonika T.; Bahinskaya, Ilona; Pinzon, Natalia; Zhang, Jianhua; Heisler, Lawrence E.; Krzyzanowski, Paul M.; Lam, Bernard; Lungu, Ilinca M.; Manase, Dorin; Pace, Krista M.; Mashouri, Pouria; Brudno, Michael; Garrels, Michael; Mazzulli, Tony; Cybulsky, Myron; Humar, Atul; Kumar, Deepali

Health care workers (HCWs) are at higher risk for SARS-CoV-2 infection and may play a role in transmitting the infection to vulnerable patients and members of the community. This is particularly worrisome in the context of asymptomatic infection. We performed a cross-sectional study looking at asymptomatic SARS-CoV-2 infection in HCWs. We screened asymptomatic HCWs for SARS-CoV-2 via PCR. Complementary viral genome sequencing was performed on positive swab specimens. A seroprevalence analysis was also performed using multiple assays. Asymptomatic health care worker cohorts had a combined swab positivity rate of 29/5776 (0.50%, 95%CI 0.32–0.75) relative to a comparative cohort of symptomatic HCWs, where 54/1597 (3.4%) tested positive for SARS-CoV-2 (ratio of symptomatic to asymptomatic 6.8:1). SARS-CoV-2 seroprevalence among 996 asymptomatic HCWs with no prior known exposure to SARS-CoV-2 was 1.4–3.4%, depending on assay. A novel in-house Coronavirus protein microarray showed differing SARS-CoV-2 protein reactivities and helped define likely true positives vs. suspected false positives. Our study demonstrates the utility of routine screening of asymptomatic HCWs, which may help to identify a significant proportion of infections.