Retrospective mortality and prevalence of SARS-CoV-2 antibodies in greater Omdurman, Sudan: a population-based cross-sectional survey

Background Even after adjusting for the expected lower severity due to the younger age of the population, relatively low SARS–CoV–2 incidence and mortality rates have been reported throughout Africa. For investigating whether this is truly the case, we conducted a survey to estimate the COVID–19 related mortality and cumulative incidence of SARS–CoV–2 infections in Omdurman the most populated city of the tripartite metropolis Khartoum in Sudan. Methods A retrospective, cross–sectional, mortality and seroprevalence survey was conducted in Omdurman, Sudan, from March 1, until April 10 2021. A two–stage cluster sampling method was used to investigate the death rate for the pre–pandemic (January 1, 2019–February 29, 2020) and pandemic (March 1, 2020 – day of the survey) period using questionnaires. The seroprevalence survey was performed in a subset of households and all consenting members were tested with a rapid serological test (SD–Biosensor) and a subgroup additionally with ELISA (EUROIMMUN). Fisher′s exact test was used to assess differences between the pre–and pandemic periods and a random effect and Bayesian latent class model to adjust for test performance. Findings Data from 27315 people (3716 households) for the entire recall period showed a 67% (95% CI 32–110) increase in death rate between the pre–pandemic (0.12 deaths/10000 people/day [95% CI 0.10–0.14]) and pandemic (0.20 [0.16–0.23]) periods. Notably, a 74% (30–133) increase in death was observed among people aged ≥50 years. The adjusted seroprevalence of SARS–CoV–2 was 54.6% (95% CI 51.4–57.8). The seroprevalence was significantly associated with age, increasing up to 80.7% (71.7–89.7) for the oldest age group (≥50 years). Interpretation Our results showed a significant elevated mortality for the pandemic period with a considerable excess mortality in Omdurman, Sudan. The overall high seroprevalence indicated a different age pattern compared to other countries, with a significant increase by age. Funding Medecins Sans Frontieres