Characteristics associated with SARS-CoV-2 testing, infection and vaccine uptake among essential non-healthcare workers in Montréal, 2021

Background Essential non-healthcare workers experienced higher rates of SARS-CoV-2 infection compared to non-essential workers. Objective Identify characteristics associated with SARS-CoV-2 testing, infection and vaccine uptake among essential non-healthcare workers in Montréal, Québec. Methods Secondary, cross-sectional analysis of data collected from participants prospectively recruited in two observational studies (first study, Onsite Testing Study, January–March 2021; second study, Self-Testing Study, July–October 2021) of essential non-healthcare workers in 2021. Logistic regression with generalized linear mixed models was used to explore characteristics associated with our outcomes (previous SARS-CoV-2 testing, exposure and vaccination). Results Overall, 2,755 participants were included (first study, Onsite Testing Study, n=2,128; and second study, Self-Testing Study, n=627). A higher proportion of participants identified as male (n=1,601; 58%), non-White (n=1,527; 55%) and worked in the manufacturing/supplier sector (n=1,706; 62%). Relative to the first study, Onsite Testing Study, participants in the second study, Self-Testing Study, had higher odds (78% vs. 46%; aOR 4.1, 95% CI: 3.2–5.2) of previous SARS-CoV-2 testing and of testing positive prior to study enrolment (6.2% vs. 4.3%; aOR 1.7, 95% CI: 1.1–2.6). Individuals reporting recent SARS-CoV-2 exposure had higher odds of previous SARS-CoV-2 testing (aOR 4.0, 95% CI: 3.0–5.4), while older age (aOR 0.98, 95% CI: 0.98–0.99 per one-year increase) and being male (aOR 0.6, 95% CI: 0.5–0.7) were associated with lower odds of previous testing. Results were similar in stratified analyses. Participants from businesses with more than 50 employees had higher odds of having received a SARS-CoV-2 vaccine (91% vs. 80%; aOR 2.6, 95% CI: 1.4–4.8). Conclusion Consideration of individual and business characteristics associated with testing and vaccination programs for SARS-CoV-2 could improve equity, uptake and impact.


Introduction
The SARS-CoV-2 transmission continues globally (1).Certain populations have been differentially impacted by SARS-CoV-2, such as visible minorities and those with jobs considered "high risk" (2).Notably, essential non-healthcare workers working in-person have experienced higher rates of SARS-CoV-2 infection compared to non-essential workers and those who were able to work from home (3)(4)(5)(6).In Montréal, Canada, essential non-healthcare workplaces were most commonly implicated in large outbreaks (7).
In 2021, we conducted two studies among non-healthcare essential workers in Montréal, Canada.In the first study, we visited businesses to assess onsite sampling for SARS-CoV-2 testing from January to March 2021 (8); a period with substantial public health measures to curb SARS-CoV-2 transmission and prior to the wide availability of SARS-CoV-2 vaccines.In the second study, we evaluated self-testing for SARS-CoV-2 with rapid diagnostic tests in similar businesses, from July to October 2021 (9); a period with minimal public health measures in effect and after all adults were eligible for SARS-CoV-2 vaccination (10).These studies, conducted among similar populations during periods with differential public health measures and vaccine availability, provide an opportunity to better understand characteristics associated with SARS-CoV-2 testing and infection, vaccine uptake and population behaviours.
The aim of this study was to leverage data collected during two prospective studies among individuals from non-healthcare businesses in Montréal in 2021, to conduct descriptive, exploratory analyses to identify characteristics associated with SARS-CoV-2 testing and infection, vaccine uptake, and population behaviours (e.g., travel outside Montréal and the province of Québec).

Study designs, participants and procedures
We conducted a secondary analysis of data collected from participants prospectively recruited in two studies.The first (hereafter, the "Onsite Testing Study") was a prospective, cross-sectional study taking place from January 27 to March 12, 2021, and the second (hereafter, the "Self-Testing Study") was a prospective, cross-sectional study from July 7 to October 8, 2021.Identical questionnaires were used in both studies except for additional questions related to vaccination in the Self-Testing Study, Appendix 1, Supplemental material.Detailed descriptions of the individual studies are available elsewhere (8,9).

Onsite Testing Study
In this study, non-healthcare essential businesses primarily within the borough of Montréal-Nord were contacted.Businesses could be of any size and eligible employees were those 18 years of age and older who were asymptomatic and who had not tested positive for SARS-CoV-2 in the previous four weeks.Our study team visited participating businesses to collect saline gargle samples for SARS-CoV-2 testing from consenting employees present on the day of our visit.

Self-Testing Study
In this study, non-healthcare businesses in the Greater Montréal Area identified by Montréal Public Health as having at least two cases of SARS-CoV-2 within the last 14 days were contacted.Participant eligibility was identical to the Onsite Testing Study.However we preferentially visited businesses with more than 50 employees.At participating businesses, consenting employees present on the day of our visit performed a SARS-CoV-2 rapid antigen detection test (Panbio TM COVID-19 Ag Rapid Test Device; Abbott Laboratories) under the supervision of the study team.

Public health measures and vaccine availability in Montréal during 2021
Public health measures and vaccine availability differed between included studies, with extensive public health measures and travel restrictions within Québec and Canada in place during the Onsite Testing Study period, and comparatively fewer measures and interprovincial travel restrictions in effect during the Self-Testing Study period.
Throughout Québec, a province-wide curfew from 8:00 p.m. to 5:00 a.m. was instituted on January 9, 2021, ending on May 28, 2021 (11,12), encompassing the entirety of the Onsite Testing Study period.With respect to travel limitations, nonessential travel was discouraged until May 28, 2021, while the border between Ontario and Québec was closed for non-essential travel from April 19 to June 16, 2021 (13,14).Public health measures also included the closing of all nonessential businesses in Montréal from December 25, 2020, until February 8, 2021 (15,16).Gradually and up to June 28, 2021, most public health measures were relaxed.Gathering and capacity limits, however, remained in place (17) and were increased on August 1, 2021.No additional public health measures were imposed until December 16, 2021, due to the Omicron variant (18,19).
The rollout of SARS-CoV-2 vaccines in Montréal began on March 1 and by May 14, 2021, all adults in Québec were eligible to receive a SARS-CoV-2 vaccine, approximately 10 weeks prior to the start of the Self-Testing Study (10,20).

Statistical analyses
We performed descriptive analyses using medians and interquartile ranges (IQR) for continuous data and proportions for categorical data for individual and business characteristics of the total population, as well as for each study population separately.Characteristics between the two study populations were compared using appropriate statistical tests (i.e., Kruskal-Wallis tests for continuous variables, and chi-squared or Fisher's exact tests for categorical variables).
Individual characteristics evaluated included age (continuous), sex (male, female), self-reported ethnicity (White, non-White), household income based on forward sortation area (top 60% income quintile, bottom 40%), self-reported presence of a health condition (yes, no) and self-reported smoking history (never, current/previous smoker).Business characteristics included sector (manufacturer/supplier, retail/consumer facing, office, childcare) and business size (50 employees or fewer, more than 50 employees).Questionnaires and data harmonization between studies are described in Appendix 2, Supplemental material, Tables S1 to S2, respectively.
We evaluated five outcomes: 1) receipt of a SARS-CoV-2 test prior to study enrolment; 2) positive SARS-CoV-2 test result more than four weeks prior to study enrolment; 3) self-reported travel outside the Montréal area or Québec in the previous 14 days; 4) known SARS-CoV-2 exposure, excluding exposure at workplaces, in the previous 14 days; and 5) receipt of at least one dose of a SARS-CoV-2 vaccine.Each outcome was evaluated in the pooled study population, except for SARS-CoV-2 vaccination, which was only available in the Self-Testing Study.
We performed logistic regression with generalized linear mixed models to estimate the adjusted odds ratio (aOR) and 95% confidence interval (CI) for each outcome, with the business sector treated as a random intercept.Models included weakly informative priors to deal with quasi-complete separation of some fixed effects observed in previous studies (8).Models were adjusted for individual and business characteristics as well as the study (to determine differences in risk between studies), as appropriate.Confounders considered included age, sex, smoking, other health factors, ethnicity, income based on forward sortation area, recent travel outside Québec, exposure to someone with SARS-CoV-2 and business size.We repeated all analyses stratified by study, sex, ethnicity, income and business sector.If directions of effect for characteristics assessed differed significantly, we assessed effect modification using likelihood ratio tests of models with versus without interaction terms.Data were analyzed using R (version 4.2.2) using base packages or the blme (version 1.0-5) and BhGLM (version 1.1.0)packages.

Ethical approval
The original studies were approved by the research ethics board of the Research Institute of the McGill University Health Centre (2021-7057 and MP-37-2022-7762), as was the present study (2023-9046).Given the nature of a secondary analysis of data for the present study, a waiver of informed consent was obtained.

Results
Overall, 2,775 participants completed a questionnaire between the two studies (Onsite Testing Study, n=2,128; Self-Testing Study, n=647), of which 2,755 were ultimately included in this analysis (Figure 1).All 20 exclusions pertained to the Self-Testing Study.
The median age of participants was 48 (IQR: 37-57) years, 1,154 (42%) were female, 1,527 (55%) identified as non-White and many (n=1,704; 62%) lived in areas with household incomes in the two lowest quintiles.Most participants (n=1,706; 62%) worked in the manufacturing/supplier sector and at businesses with more than 50 employees (n=1,755; 64%).Participant characteristics in terms of business sector and size, sex, selfreported ethnicity, and presence of health conditions varied significantly (p<0.05) between studies (Table 1).Disaggregated participant characteristics regarding ethnicity, income and business sector are in Appendix 2, Table S1.

EPIDEMIOLOGIC STUDY
Similarly, participants in the Self-Testing Study had higher odds of testing positive for SARS-CoV-2 more than four weeks prior to study enrolment (6.2% vs. 4.3%; aOR 1.7, 95% CI: 1.1-2.6)compared to those in the Onsite Testing Study (Table 3); there was no evidence (p=0.75) of effect modification by sector (Appendix 2, Table S6).We found those reporting recent SARS-CoV-2 exposure also had higher odds (aOR 3.9, 95% CI: 2.6-5.7) of testing positive.However, when limiting this analysis only to those who had previously been tested, there was no difference between studies in the odds of previously testing positive for SARS-CoV-2 (Appendix 2, Table S7).This was also the case in analyses limited to males (Appendix 2, Table S2) and those stratified on income (Appendix 2, Table S4).

EPIDEMIOLOGIC STUDY
When examining individual behaviours, participants in the Self-Testing Study had substantially higher odds (aOR 8.2, 95% CI: 5.6-12.1) of reporting recent travel outside Montréal or Québec (Table 4).Moreover, older participants (aOR 0.98, 95% CI: 0.97-0.99 per one-year increase) and those who identified as non-White (aOR 0.3, 95% CI: 0.2-0.5)had lower odds of reporting any recent travel.This was largely consistent in stratified analyses (Appendix 2, Tables S2 to S6), with evidence of effect modification (p<0.001) by business sector.When limiting this analysis to only those in the Self-Testing Study, vaccination was not associated with travel (Appendix 2, Table S8).We did not identify any difference between studies in terms of recent exposure to someone with confirmed SARS-CoV-2 in the total population (Appendix 2, Table S9), which was consistent in stratified analyses (Appendix 2, Tables S2 to S6).
Findings were consistent in stratified analyses among males and those self-identifying as White (Appendix 2, Tables S2 to S3).
In stratified analysis among those in the three highest income quintiles (Appendix 2, Table S4), participants identifying as non-White had lower odds of vaccination (aOR 0.3, 95% CI: 0.1-0.9),while participants working at businesses in the retail sector with more than 50 employees (Appendix 2, Table S6) had higher odds of vaccination (aOR 14.7, 95% CI: 3.5-61.1).We found significant effect modification on odds of vaccination by previous SARS-CoV-2 exposure and ethnicity, with those having previous exposure and self-identifying as White having significantly higher odds of vaccination compared to those self-identifying as non-White (Appendix 2, Table S3).

Figure 1 :
Figure 1: Number of participants enrolled in original studies that were ultimately included in the present analysis (n=2,755)

Table 1 :
Characteristics of included participants in each study and overall Abbreviations: IQR, interquartile range; N/A, not applicable a Recent travel defined as occurring within the previous 14 days b Information on vaccination only available for participants in the Self-Testing Study Note: Two-sided p-values are calculated using Fisher exact or chi-squared test, as appropriate for categorical data and Wilcoxon rank sum or Kruskal-Wallis test for continuous data

Table 2 :
Logistic regression results for characteristics associated with being tested for SARS-CoV-2 prior to study enrollment

Table 3 :
Logistic regression for characteristics associated with testing positive for SARS-CoV-2 more than four weeks prior to study enrollment

Table 4 :
Logistic regression for characteristics associated with any self-reported travel outside of Montréal or Québec within the 14 days prior to study enrollment

Table 5 :
Logistic regression for characteristics associated with receiving at least one dose of a vaccine against SARS-CoV-2 among the Self-Testing Study population after vaccine availability to this group Abbreviations: aOR, adjusted odds ratio; CI, confidence interval; N/A, not applicable; Ref., reference category a Business sector included as a random intercept in the model b Recent travel defined as occurring within the previous 14 days