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. 2021 Nov:112:25-34.
doi: 10.1016/j.ijid.2021.08.062. Epub 2021 Sep 2.

High seroprevalence of SARS-CoV-2 but low infection fatality ratio eight months after introduction in Nairobi, Kenya

Isaac Ngere  1 , Jeanette Dawa  1 , Elizabeth Hunsperger  2 , Nancy Otieno  3 , Moses Masika  4 , Patrick Amoth  5 , Lyndah Makayotto  6 , Carolyne Nasimiyu  1 , Bronwyn M Gunn  7 , Bryan Nyawanda  3 , Ouma Oluga  6 , Carolyne Ngunu  6 , Harriet Mirieri  1 , John Gachohi  8 , Doris Marwanga  1 , Patrick K Munywoki  2 , Dennis Odhiambo  3 , Moshe D Alando  3 , Robert F Breiman  9 , Omu Anzala  4 , M Kariuki Njenga  1 , Marc Bulterys  2 , Amy Herman-Roloff  2 , Eric Osoro  10
Affiliations

High seroprevalence of SARS-CoV-2 but low infection fatality ratio eight months after introduction in Nairobi, Kenya

Isaac Ngere et al. Int J Infect Dis. 2021 Nov.

Abstract

Background: The lower than expected COVID-19 morbidity and mortality in Africa has been attributed to multiple factors, including weak surveillance. This study estimated the burden of SARS-CoV-2 infections eight months into the epidemic in Nairobi, Kenya.

Methods: A population-based, cross-sectional survey was conducted using multi-stage random sampling to select households within Nairobi in November 2020. Sera from consenting household members were tested for antibodies to SARS-CoV-2. Seroprevalence was estimated after adjusting for population structure and test performance. Infection fatality ratios (IFRs) were calculated by comparing study estimates with reported cases and deaths.

Results: Among 1,164 individuals, the adjusted seroprevalence was 34.7% (95% CI 31.8-37.6). Half of the enrolled households had at least one positive participant. Seropositivity increased in more densely populated areas (spearman's r=0.63; p=0.009). Individuals aged 20-59 years had at least two-fold higher seropositivity than those aged 0-9 years. The IFR was 40 per 100,000 infections, with individuals ≥60 years old having higher IFRs.

Conclusion: Over one-third of Nairobi residents had been exposed to SARS-CoV-2 by November 2020, indicating extensive transmission. However, the IFR was >10-fold lower than that reported in Europe and the USA, supporting the perceived lower morbidity and mortality in sub-Saharan Africa.

Keywords: COVID-19 pandemic; Disease underreporting; Infection underestimation; SARS-CoV-2; Seroprevalence.

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Figures

Figure 1
Figure 1
Study enrolment flow chart for the SARS-CoV-2 antibody prevalence survey in Nairobi City County, November 2020
Figure 2
Figure 2
Sub-county seroprevalence positivity and population density per kilometre2.
Figure 3
Figure 3
Multivariable mixed effects logistic regression of factors associated with SARS-CoV-2 seropositivity, Nairobi city county. The 0-9 years group was used as the reference age category. The adjusted odds ratios for each variable are indicated as a black dot, with the confidence intervals on either side.
See this image and copyright information in PMC

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