Abstract
BackgroundSerosurveys for SARS-CoV-2 aim to estimate the proportion of the population that has been infected.AimThis observational study assesses the seroprevalence of SARS-CoV-2 antibodies in Ontario, Canada during the first pandemic wave.MethodsUsing an orthogonal approach, we tested 8,902 residual specimens from the Public Health Ontario laboratory over three time periods during March–June 2020 and stratified results by age group, sex and region. We adjusted for antibody test sensitivity/specificity and compared with reported PCR-confirmed COVID-19 cases.ResultsAdjusted seroprevalence was 0.5% (95% confidence interval (CI): 0.1–1.5) from 27 March–30 April, 1.5% (95% CI: 0.7–2.2) from 26–31 May, and 1.1% (95% CI: 0.8–1.3) from 5–30 June 2020. Adjusted estimates were highest in individuals aged ≥ 60 years in March–April (1.3%; 95% CI: 0.2–4.6), in those aged 20–59 years in May (2.1%; 95% CI: 0.8–3.4) and in those aged ≥ 60 years in June (1.6%; 95% CI: 1.1–2.1). Regional seroprevalence varied, and was highest for Toronto in March–April (0.9%; 95% CI: 0.1–3.1), for Toronto in May (3.2%; 95% CI: 1.0–5.3) and for Toronto (1.5%; 95% CI: 0.9–2.1) and Central East in June (1.5%; 95% CI: 1.0–2.0). We estimate that COVID-19 cases detected by PCR in Ontario underestimated SARS-CoV-2 infections by a factor of 4.9.ConclusionsOur results indicate low population seroprevalence in Ontario, suggesting that public health measures were effective at limiting the spread of SARS-CoV-2 during the first pandemic wave.
Highlights
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease (COVID-19), emerged as a novel pathogen in December 2019 [1] and has resulted in a global pandemic, with over 100 million cases and ca 2 million deaths reported by the end of January 2021 [2]
To ensure that serosurvey results contribute to the Canadian pandemic response in a timely manner, some of the results presented here were published on the Public Health Ontario website [13]
Samples that were positive with the Architect SARS-CoV-2 IgG assay were tested using the VITROS anti-SARSCoV-2 IgG assay, which detects anti-spike antibodies (Ortho-Clinical Diagnostics, Raritan, New Jersey, US)
Summary
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease (COVID-19), emerged as a novel pathogen in December 2019 [1] and has resulted in a global pandemic, with over 100 million cases and ca 2 million deaths reported by the end of January 2021 [2]. The first wave of the pandemic peaked in Ontario in mid-April, with declining case numbers through the summer of 2020, and a cumulative total by July 31, 2020 of nearly 40,000 cases and 2,800 deaths [7]. This number, which represents PCR-confirmed COVID19 cases reported to Public Health Ontario (PHO), does not capture everyone in the population who has been infected, since not every infected individual is tested and reported [8]. Conclusions: Our results indicate low population seroprevalence in Ontario, suggesting that public health measures were effective at limiting the spread of SARS-CoV-2 during the first pandemic wave
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