Healthcare-acquired coronavirus disease 2019 (COVID-19) is less symptomatic than community-acquired disease among healthcare workers

Abstract

Objective: We hypothesized that healthcare workers (HCWs) with high-risk exposures outside the healthcare system would have less asymptomatic coronavirus 2019 (COVID-19) disease and more symptoms than those without such exposures.

Design: A longitudinal point prevalence study was conducted during August 17-September 4, 2020 (period 1) and during December 2-23, 2020 (period 2).

Setting: Community based teaching health system.

Participants: All HCWs were invited to participate. Among HCWs who acquired COVID-19, logistic regression models were used to evaluate the adjusted odds of asymptomatic disease using high-risk exposure outside the healthcare system as the explanatory variable. The number of symptoms between exposure groups was evaluated with the Wilcoxon rank-sum test. The risk of seropositivity among all HCS by work exposure was evaluated during both periods.

Interventions: Survey and serological testing.

Result: Seroprevalence increased from 1.9% (95% confidence interval [CI], 1.2%-2.6%) to 13.7% (95% CI, 11.9%-15.5%) during the study. Only during period 2 did HCWs with the highest work exposure (versus low exposure) have an increased risk of seropositivity (risk difference [RD], 7%; 95% CI, 1%-13%). Participants who had a high-risk exposure outside of work (compared to those without) had a decreased probability of asymptomatic disease (odds ratio [OR], 0.38; 95% CI, 0.16-0.86) and demonstrated more symptoms (median 3 [IQR, 2-6] vs 1 [IQR, 0-4]; P = .001).

Conclusions: Healthcare-acquired COVID-19 increases the probability of asymptomatic or mild COVID-19 disease compared to community-acquired disease. This finding suggests that infection prevention strategies (including masks and eye protection) may be mitigating inoculum and supports the variolation theory in COVID-19.

Fig. 1.

Epidemiology of COVID-19 during the study periods. A surge of cases April was centered in southeastern Michigan with a later surge moderate surge in cases in Kent County, May–June 2020. A larger surge occurred in Michigan that disproportionately affected western Michigan.

Fig. 2.

The risk difference and 95% CI between higher and lower exposure groups during study periods 1 and 2. During period 2, healthcare workers at the highest exposure risk had an increased probability COVID-19 by seropositivity to SARS-CoV-2 antibodies.

Fig. 3.

Cohort for the primary outcome.

Fig. 4.

High-risk exposure outside work and number of symptoms in participants who developed COVID-19.