COVID Testing in the Workplace: Return to Work Testing in an Occupational Cohort

Background. The Omicron SARS-CoV-2 variant resulted in significant community-based transmission. Numerous occupational settings have employed surveillance testing strategies to minimize occupational exposure and return workers safely to work following isolation. Methods. From an occupational COVID-19 testing program, we obtained longitudinal (February 2021-January 2022) saliva-based RT-qPCR results and starting December 27th, 2021, daily on-site molecular over-the-counter (OTC) nasal swab-based isothermal nucleic acid amplification test (molecular OTC; Cue Health COVID-19 test) results. We quantified the fraction of tests with PCR cycle threshold (Ct) values <30 on each day post detection from suspected and confirmed Omicron infections (n=37), compared results to molecular OTC testing, and measured workplace and household transmission. We evaluated return-to-work timing using a post-isolation, two-test threshold of Ct >30, or two negative molecular OTC tests over a 24 hour period, or a single PCR test >30 plus negative molecular OTC test. Results. From the paired testing cohort, 37 (48%) individuals tested positive; all 37 were vaccinated. All individuals tested positive [≤]1 day after a previous negative test, and 19 (51.3%) remained PCR-positive with Ct values <30 at day 5. While 3 (8.1%) remained PCR-positive with a Ct value <30 on day 10, no individuals remained PCR-positive on day 12. The average time to PCR clearance/return-to-work was 7.94 days (median=9.5 days). Time to clearance for those boosted (n=8; 7.75 days) and those not yet boosted (8.04 days) did not differ (p=0.49). Peak viral load measured by PCR was 1.97 days from the initial positive test. There were no cases of transmission after returning to work. Conclusions. A large percentage of individuals remain contagious at day 5 post first positive test based on serial PCR testing and can continue until day 12. Early discontinuation of isolation can utilize a two test framework separated by 24 hours. Rapid onsite tests may be useful.