SARS-CoV-2 Seroprevalence in a Rural and Urban Household Cohort during First and Second Waves of Infections, South Africa, July 2020-March 2021

Abstract

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections may be underestimated because of limited access to testing. We measured SARS-CoV-2 seroprevalence in South Africa every 2 months during July 2020-March 2021 in randomly selected household cohorts in 2 communities. We compared seroprevalence to reported laboratory-confirmed infections, hospitalizations, and deaths to calculate infection-case, infection-hospitalization, and infection-fatality ratios in 2 waves of infection. Post-second wave seroprevalence ranged from 18% in the rural community children <5 years of age, to 59% in urban community adults 35-59 years of age. The second wave saw a shift in age distribution of case-patients in the urban community (from persons 35-59 years of age to persons at the extremes of age), higher attack rates in the rural community, and a higher infection-fatality ratio in the urban community. Approximately 95% of SARS-CoV-2 infections were not reported to national surveillance.

Keywords: COVID-19; SARS-CoV-2; South Africa; coronavirus disease; coronaviruses; infection–case ratio; infection–fatality ratio; infection–hospitalization ratio; respiratory infections; seroprevalence; severe acute respiratory syndrome coronavirus 2; viruses; zoonoses.

Figure 1

Timing of blood collection and weekly incidence of severe acute respiratory syndrome coronavirus 2 infection in the rural community district (A) and the urban community district (B), South Africa, March 2020–March 2021. BD, blood draw.

Figure 2

Seroprevalence of severe acute respiratory syndrome coronavirus 2 at each blood collection, by age group, in a rural community (A) and an urban community (B), South Africa, March 2020–March 2021.

Figure 3

Age- and sex-standardized number of severe acute respiratory syndrome coronavirus 2 infections, laboratory-confirmed diagnoses, hospitalizations, and deaths per 100,000 population in a rural community during infection wave 1 (A) and wave 2 (B) and an urban community during infection wave 1 (C) and wave 2 (D), South Africa, March 2020–March 2021. CrI, credible interval.

Figure 4

Severe acute respiratory syndrome coronavirus 2 infection–case and infection–hospitalization ratios (A) and in-hospital and excess deaths infection-fatality ratios (B) in a rural and urban community during the first and second wave of infections, South Africa, March 2020–March 2021. Vertical lines represent 95% CIs. Wave 1: March 1–November 21, 2020. Wave 2: November 2020 22–March 27, 2021. ED, excess deaths; ICR, infection–case ratio; IFR, infection–fatality ratio; IH, in-hospital; IHR, infection–hospitalization ratio.

Figure 5

Cutoff index (COI) on Roche Elecsys (Roche Diagnostics, https://www.roche.ch/en/standorte/rotkreuz.htm) anti–severe acute respiratory syndrome coronavirus 2 assay for persons with blood draws 1–5 samples who were seropositive at baseline (A) or showed seroconversion during blood draws 2–5, South Africa, July 2020–April 2021. Purple line indicates mean COI with 95% CIs. COI values in panel B are aligned to first draw before seroconversion, COI, cutoff index.