Background Pre-symptomatic subjects are spreaders of SARS-CoV-2 infection, and strategies that could identify these subjects, particularly in hospital settings, are needed. Methods We tested a cohort of 9449 employees at work at the Karolinska University Hospital, Stockholm, Sweden for SARS-CoV-2 RNA and antibodies, linked the screening results to sick leave records and examined the association between screening results and past or future sick leave using multinomial logistic regression. Results We found that healthcare workers with high amounts of SARS-CoV-2 virus, as indicated by the Cycle threshold (Ct) value in the PCR, had the highest risk for sick leave in the two weeks after testing (OR 11.97 (CI 95% 6.29-22.80)) whereas subjects with low amounts of virus had the highest risk for sick leave in the past three weeks before testing (OR 6.31 (4.38-9.08)). Only 2.5% of employees were SARS-CoV-2 positive while 10.5% were positive by serology and 1.2% were positive in both tests. Serology-positive subjects were not at excess risk for future sick leave (OR 1.06 (95% CI, 0.71-1.57)), but virus-positive subjects had a 7.23 fold (95% CI, 4.52-11.57)) increased risk for sick leave within two weeks post testing. Conclusions Screening of asymptomatic healthcare workers for high amounts of SARS-CoV-2 virus using Ct values will identify pre-symptomatic subjects who will develop disease in the next few weeks. Identification of potentially contagious, pre-symptomatic subjects is likely critical for protecting patients and healthcare workers.
Screening for high amounts of SARS-CoV-2 identifies pre-symptomatic subjects among healthy healthcare workers