Estimating the seroprevalence of SARS-CoV-2 infections: systematic review

Byambasuren, O.; Dobler, C. C.; Bell, K.; Rojas, D. P.; Clark, J.; McLaws, M.-L.; Glasziou, P.

Abstract Background: Accurate seroprevalence estimates of SARS-CoV-2 in different populations could help gauge the true magnitude and spread of the infection seroprevalence. Reported estimates have varied greatly, but many have derived from biased samples, and inadequate testing methods. Objective: To estimate the range of valid seroprevalence rates of SARS-CoV-2 in different populations, and compare these seroprevalence estimates with the cumulative cases seen in the same population. Methods: We searched PubMed, Embase, the Cochrane COVID-19 trials, and Europe-PMC for published studies and pre-prints from January 2020 to 25 May 2020 that reported anti-SARS-CoV-2 IgG, IgM and/or IgA antibodies for serosurveys of either the general community or of defined sub-populations, such healthcare workers and other organizations. Results: Of the 837 studies identified, 49 were assessed and 14 were includable. Included studies represented 10 countries and 100,557 subjects: 9 from randomly selected populations, 2 from healthcare workers, 2 from industry populations, and 1of parturient women. The seroprevalence proportions in 10 studies ranged between 1%-10%, and 2 study estimates under 1%, and 2 over 10% - from the notably hard-hit regions of Gangelt in Germany and from Northwest Iran. The two studies in healthcare workers, in Italy and Spain, had seroprevalence rates at higher range of estimates, with the Barcelona hospitals having a higher rate than the Spanish national survey. For only one study was the seroprevalence estimate higher than the cumulative incidence, though these were proximate for several studies. In five studies, the seroprevalence was similar to the cumulative case numbers in the same population. For seropositive cases not previously detected as COVID-19 cases, the majority had prior COVID-like symptoms. Conclusion: The seroprevalence of SARS-CoV-2 mostly less than 10% with the level of infection lower in the general community, suggesting levels well below herd immunity. The similarity of seroprevalence and reported cases is several studies, and high symptom rates in seropositive cases suggest that gaps between seroprevalence rates and reported cases are likely due to undertesting of symptomatic people.