PT  - JOURNAL ARTICLE
AU  - Science, Michelle
AU  - Bolotin, Shelly
AU  - Silverman, Michael
AU  - Nadarajah, Jeya
AU  - Maguire, Bryan
AU  - Parekh, Rulan S.
AU  - McGeer, Allison
AU  - Schwartz, Kevin L.
AU  - Alexander, Laura
AU  - Allen, Upton
AU  - Ariyarajah, Archchun
AU  - Castellani, Lucas
AU  - Cohn, Ronald D.
AU  - Downing, Mark
AU  - Katz, Kevin
AU  - Kazmi, Kescha
AU  - Leis, Jerome A.
AU  - Liu, Derek
AU  - Pernica, Jeffrey M.
AU  - Schneiderman, Jane E.
AU  - Sumaida, Maya
AU  - Campigotto, Aaron
TI  - SARS-CoV-2 antibodies in Ontario health care workers during and after the first wave of the pandemic: a cohort study
AID  - 10.9778/cmajo.20210044
DP  - 2021 Oct 01
TA  - CMAJ Open
PG  - E929--E939
VI  - 9
IP  - 4
4099  - http://www.cmajopen.ca/content/9/4/E929.short
4100  - http://www.cmajopen.ca/content/9/4/E929.full
SO  - CMAJ2021 Oct 01; 9
AB  - Background: Health care workers have a critical role in the pandemic response to COVID-19 and may be at increased risk of infection. The objective of this study was to assess the seroprevalence of SARS-CoV-2 immunoglobulin G (IgG) antibodies among health care workers during and after the first wave of the pandemic.Methods: We conducted a prospective multicentre cohort study involving health care workers in Ontario, Canada, to detect IgG antibodies against SARS-CoV-2. Blood samples and self-reported questionnaires were obtained at enrolment, at 6 weeks and at 12 weeks. A community hospital, tertiary care pediatric hospital and a combined adult–pediatric academic health centre enrolled participants from Apr. 1 to Nov. 13, 2020. Predictors of seropositivity were evaluated using a multivariable logistic regression, adjusted for clustering by hospital site.Results: Among the 1062 health care workers participating, the median age was 40 years, and 834 (78.5%) were female. Overall, 57 (5.4%) were seropositive at any time point (2.5% when participants with prior infection confirmed by polymerase chain reaction testing were excluded). Seroprevalence was higher among those who had a known unprotected exposure to a patient with COVID-19 (p < 0.001) and those who had been contacted by public health because of a nonhospital exposure (p = 0.003). Providing direct care to patients with COVID-19 or working on a unit with a COVID-19 outbreak was not associated with higher seroprevalence. In multivariable logistic regression, presence of symptomatic contacts in the household was the strongest predictor of seropositivity (adjusted odds ratio 7.15, 95% confidence interval 5.42–9.41).Interpretation: Health care workers exposed to household risk factors were more likely to be seropositive than those not exposed, highlighting the need to emphasize the importance of public health measures both inside and outside of the hospital.