Dataset Information

SARS-CoV-2 seroprevalence among blood donors in Quebec, and analysis of symptoms associated with seropositivity: a nested case-control study.

ABSTRACT:

Objectives

A substantial proportion of individuals infected with SARS-CoV-2 do not experience noticeable symptoms typical of COVID-19. Our objectives were to evaluate the impact of the first wave of the pandemic in Québec by measuring SARS-CoV-2 antibody seroprevalence in a convenience sample of healthy blood donors and to study the association between seropositivity and the occurrence of COVID-19 symptoms.

Methods

The study design was a cross-sectional serological survey with a nested case-control study. Residual blood samples from donations collected between May 25 and July 9, 2020 (well before vaccination rollout) in the province of Québec were tested for anti-Spike RBD antibodies by ELISA. Seropositive donors and a control group of seronegative donors were questioned about prior COVID-19 symptoms. All qualified blood donors were eligible for participation.

Results

A total of 7691 blood donors were included in the study. After adjustments, the seroprevalence rate was 2.2% (95% CI 1.9-2.6). Seropositive donors reported one or more symptoms in a proportion of 52.2% (95% CI 44.2-60.1); this proportion was 19.1% (95% CI 13.4-26.1) among seronegative donors, suggesting that approximately 50-66% of all infections were asymptomatic. Univariate analysis of associations between symptoms and seropositivity revealed that except for rhinorrhea, all symptoms were significantly associated with seropositivity.

Conclusion

Assuming that blood donors are fairly representative of the general adult population, this study shows that less than 3% of 18-69-year-olds have been infected during the first wave of the pandemic in the province of Québec. Our data also confirm that many infections escaped detection, including a substantial proportion that were asymptomatic.

SUBMITTER: Lewin A

PROVIDER: S-EPMC8127462 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundSARS-CoV-2 seroprevalence monitors cumulative infection rates irrespective of case testing protocols. We aimed to describe Nova Scotia blood donor seroprevalence in relation to public health policy and reported data over the course of the COVID-19 pandemic (May 2020 to August 2022).MethodsMonthly random Nova Scotia blood donation samples (24,258 in total) were tested for SARS-CoV-2 infection antibodies (anti-nucleocapsid) from May 2020 to August 2022, and vaccination antibodies (anti-spike) from January 2021 to August 2022. Multivariable logistic regression for infection antibodies and vaccination antibodies separately with month, age, sex, and racialization identified independent predictors. The provincial nucleic acid amplification test (NAAT)-positive case rate over the pandemic was calculated from publicly available data.ResultsAnti-N seroprevalence was 3.8% in January 2022, increasing to 50.8% in August 2022. The general population COVID-19 case rate was 3.5% in January 2022, increasing to 12.5% in August 2022. The percentage of NAAT-positive samples in public health laboratories increased from 1% in November 2021 to a peak of 30.7% in April 2022 with decreasing numbers of tests performed. Higher proportions of younger donors as well as Black, Indigenous, and racialized blood donors were more likely to have infection antibodies (p < 0.01). Vaccination antibodies increased to 100% over 2021, initially in older donors (60+ years), and followed by progressively younger age groups.ConclusionsSARS-CoV-2 infection rates were relatively low in Nova Scotia until the more contagious Omicron variant dominated, after which about half of Nova Scotia donors had been infected despite most adults being vaccinated (although severity was much lower in vaccinated individuals). Most COVID-19 cases were detected by NAAT until Omicron arrived. When NAAT testing priorities focused on high-risk individuals, infection rates were better reflected by seroprevalence.

Project description:We monitored the seroprevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleocapsid (anti-N; proxy of natural infection) and spike protein (anti-S; proxy for humoral immunity) antibodies in blood donors across Canada from January to November 2021. The first and second doses of vaccine were deployed over this time. Anti-N seroprevalence remained low overall (about 5% or lower) from January to November but was higher in racialized groups, younger age groups, and those living in materially deprived neighborhoods. Anti-S seroprevalence corresponded with the roll out of vaccines across the country, increasing in April in older donors and then progressively to younger age groups consistent with vaccination policies targeting oldest to youngest. By November, close to 100% of blood donors were positive for anti-S. Anti-S concentrations peaked by July and began waning by September to November particularly in older donors. These data have informed national and provincial public health policy in Canada throughout vaccination rollout. IMPORTANCE Throughout the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, our blood donor seroprevalence study has informed Canadian public health policy at national and provincial levels. We describe the only continuously running national seroprevalence study in Canada, which spans the full length of the pandemic and per capita is one of the largest programs in the world. The benefit of seroprevalence studies is that they identify a broad range of asymptomatic and symptomatic infection histories that may not be identified with active SARS-CoV-2 nucleic acid testing programs or when case definitions change. As vaccination was deployed in Canada, we estimated the proportion of donors with vaccine-related antibodies and developed population-level estimates of SARS-CoV-2 spike antibody concentrations. Monthly predictive mathematical models and our results engaged public health organizations in new ways. In the future, we intend to continue to expand on these interactions with provincial and national public health teams.