Reduced SARS-CoV-2 Infection Rates in Lab Workers Conducting Nucleic Acid Testing: Controlling for the Healthy Worker Effect.

Abstract

Background: During the COVID-19 outbreak in December 2022 in China, some laboratory workers in SARS-CoV-2 nucleic acid testing (NAT) laboratories remained uninfected.

Objectives: To evaluate if the incidence of SARS-CoV-2 infection was reduced in laboratory workers who performed SARS-CoV-2 NAT, and whether this reduction resulted from the healthy worker effect.

Methods: This retrospective cohort study included 423 laboratory workers from 14 SARS-CoV-2 NAT laboratories in Xiamen, China. The incidence of SARS-CoV-2 infection among laboratory workers was analysed based on whether and how long they were engaged in NAT. The healthy worker effect among the laboratory workers engaged in NAT was examined.

Results: The incidence of SARS-CoV-2 infection was lower in workers engaged in SARS-CoV-2 NAT, with a gradual reduction observed as the cumulative time of SARS-CoV-2 NAT increased. A healthy worker effect was observed and eliminated after matching and stratification based on gender, age, education level, and vaccination. Workers who had ever participated in SARS-CoV-2 NAT had a lower cumulative probability of SARS-CoV-2 infection and a longer duration from vaccination to SARS-CoV-2 infection, and this trend was found to be more prominent with a longer cumulative time to SARS-CoV-2 NAT.

Conclusions: A reduction in SARS-CoV-2 infections was observed among laboratory workers conducting SARS-CoV-2 NAT after controlling for the healthy worker effect. This finding has broader implications for understanding the role of natural immunity and its interaction with vaccine immunity in defending against SARS-CoV-2 infection.