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. 2023 Apr:134:97-107.
doi: 10.1016/j.jhin.2023.01.018. Epub 2023 Feb 16.

Comparison of risk factors for SARS-CoV-2 infection among healthcare workers during Omicron and Delta dominance periods in Japan

Y Li  1 , S Yamamoto  1 , Y Oshiro  2 , N Inamura  2 , T Nemoto  2 , K Horii  3 , J S Takeuchi  4 , T Mizoue  5 , M Konishi  1 , M Ozeki  2 , H Sugiyama  6 , W Sugiura  7 , N Ohmagari  8
Affiliations

Comparison of risk factors for SARS-CoV-2 infection among healthcare workers during Omicron and Delta dominance periods in Japan

Y Li et al. J Hosp Infect. 2023 Apr.

Abstract

Background: The risk factors for coronavirus disease (COVID-19) among healthcare workers (HCWs) might have changed since the emergence of the highly immune evasive Omicron variant.

Aim: To compare the risk factors for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection among HCWs during the Delta- and Omicron-predominant periods.

Methods: Using data from repeated serosurveys among the staff of a medical research centre in Tokyo, two cohorts were established: Delta period cohort (N = 858) and Omicron period cohort (N = 652). The potential risk factors were assessed using a questionnaire. Acute/current or past SARS-CoV-2 infection was identified by polymerase chain reaction or anti-nucleocapsid antibody tests, respectively. Poisson regression was used to calculate the risk ratio (RR) of infection risk.

Findings: The risk of SARS-CoV-2 infection during the early Omicron-predominant period was 3.4-fold higher than during the Delta-predominant period. Neither working in a COVID-19-related department nor having a higher degree of occupational exposure to SARS-CoV-2 was associated with an increased infection risk during both periods. During the Omicron-predominant period, infection risk was higher among those who spent ≥30 min in closed spaces, crowded spaces, and close-contact settings without wearing mask (≥3 times versus never: RR: 6.62; 95% confidence interval: 3.01-14.58), whereas no such association was found during the Delta period.

Conclusion: Occupational exposure to COVID-19-related work was not associated with the risk of SARS-CoV-2 infection in the Delta or Omicron period, whereas high-risk behaviours were associated with an increased infection risk during the Omicron period.

Keywords: COVID-19; Delta variant; Healthcare workers; Omicron variant; SARS-CoV-2.

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Figures

Figure 1
Figure 1
Timeline of antibody surveys, vaccine dates among National Center for Global Health and Medicine staff, and changes in the number of newly confirmed COVID-19 cases in Japan.
Figure 2
Figure 2
Flowchart of the study design and participant selection.
See this image and copyright information in PMC

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Supplementary concepts