SARS-CoV-2 seroprevalence among blood donors after the first COVID-19 wave in Canada

Abstract

Background: Case detection underestimates the burden of the COVID-19 pandemic. Following the first COVID-19 wave, we estimated the seroprevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) among blood donors across Canada.

Study design and methods: This serial cross-sectional study was conducted between May 9 and July 21, 2020 from blood donors donating at all Canadian Blood Services locations. We used the Abbott Architect assay to detect SARS-CoV-2 IgG antibodies from retention plasma. Seroprevalence was standardized to population-level demographics and assay characteristics were adjusted using the Rogan-Gladen equation. Results were stratified by region, age, ethnicity, ABO groups, and quantiles of material and social deprivation indices. Temporal trends were evaluated at 2-week intervals. Univariate and multivariate logistic regression compared SARS-CoV-2 reactive to non-reactive donors by sociodemographic variables.

Results: Overall 552/74642 donors, had detectable antibodies, adjusted seroprevalence was 7.0/1000 donors (95% CI; 6.3, 7.6). Prevalence was differential by geography, Ontario had the highest rate, 8.8/1000 donors (7.8, 9.8), compared to the Atlantic region 4.5/1000 donors (2.6, 6.4); adjusted odds ratio (aOR) 2.2 (1.5, 3.3). Donors that self-identified as an ethnic minority were more likely than white donors to be sero-reactive aOR 1.5 (1.2, 1.9). No temporal trends were observed.

Discussion: Worldwide, blood services have leveraged their operational capacity to inform public health. While >99% of Canadians did not show humoral evidence of past infection, we found regional variability and disparities by ethnicity. Seroprevalence studies will continue to play a pivotal role in evaluating public health policies by identifying trends and monitor disparities.

Keywords: COVID-19; Canada; SARS-CoV-2 seroprevalence; blood donors.

FIGURE 1

Seroprevalence by economic region across Canada. This map of Canada is divided by economic region (a grouping of census divisions derived by postal codes) a standard geographic unit for analysis. The seroprevalence rate is expressed per 1000 donors, darker shades represent greater seroprevalence. Seroprevalence was not calculated for regions with <200 donors (represented as white)

FIGURE 2

Temporal trends of SARS‐CoV‐2 Seroprevalence from May 9, 2020 to July 21, 2020. Temporal trends were assessed at approximately 2‐week intervals: Week 1‐2 (May 9–May 23); Week 3‐4 (May 24‐Jun 7); Week 5‐6 (Jun 8‐ Jun 22); Week 7‐8 (Jun 23‐ Jul 7); Week 9‐10 (Jul 8‐Jul 21). Panel (A) summarizes temporal trends of adjusted seroprevalence rates overall. Panel (B) stratifies adjusted seroprevalence by geographical region. All rates are expressed, per 1000 donors and 95% CI