Cohort profile: Recruitment and retention in a prospective cohort of Canadian health care workers during the Covid-19 pandemic.

PurposeHealth care workers (HCWs) were recruited early in 2020 to chart effects on their health as the COVID-19 pandemic evolved. The aim was to identify modifiable workplace risk factors for infection and mental ill-health. ParticipantsParticipants were recruited from four Canadian provinces, physicians (MDs) in Alberta, British Columbia, Ontario and Quebec, registered nurses (RNs), licensed practical nurses (LPNs) and health care aides (HCAs) in Alberta and personal support workers (PSWs) in Ontario. Volunteers gave blood for serology testing before and after vaccination. Cases with COVID-19 were matched with up to 4 referents in a nested case-referent study. Findings to Date4964/5130 (97%) of those recruited joined the longitudinal cohort: 1442 MDs, 3136 RNs, 71 LPNs, 235 PSWs, 80 HCAs. Overall, 3812 (77%) were from Alberta. Pre-pandemic risk factors for mental ill-health and respiratory illness differed markedly by occupation. Participants completed questionnaires at recruitment, fall 2020, spring 2021, and spring 2022. By the 4th contact, 127 had retired, moved away or died, for a response rate of 89% (4299/4837). 4567/4864 (92%) received at least one vaccine shot: 2752/4567 (60%) gave post-vaccine blood samples. Ease of accessing blood collection sites was a strong determinant of participation. Among 533 cases and 1697 referents recruited to the nested case-referent study, risk of infection at work decreased with widespread vaccination. Future PlansSerology results (concentration of immunoglobulin G (IgG)) together with demographic data will be entered into the publicly accessible database compiled by the Canadian Immunology Task Force. Linkage with provincial administrative health databases will permit case validation, investigation of longer-term sequalae of infection and comparison with community controls. Analysis of the existing dataset will concentrate on effects on IgG of medical condition, medications and stage of pregnancy, and the role of occupational exposures and supports on mental health during the pandemic. Strengths and limitationsO_LIRecruitment of a broad spectrum of health care workers close to the start of the COVID-19 pandemic through their professional organizations C_LIO_LIConsent to link to records held by public health departments allows for validation of self-reports of vaccinations and episodes of COVID-19 infection C_LIO_LIRepeated contacts permit charting the evolution of anxiety, depression and sources of stress through the course of the pandemic C_LIO_LIThe inclusion of a nested case-referent study allows exposure reporting in near real time C_LIO_LIThe absence of good denominator data limits the ability to examine recruitment bias C_LI N=4216