Statistical analysis
For the analysis, only those who tested positive on both WANTAI and
Abbott assays were classified as SARS-CoV-2 antibody positive (Figure
1). Those who tested negative on only one or both assays were classified
as negative.
Sampling weights were calculated based on selection probabilities at
each site. Non-response weights (for questionnaire and each laboratory
test) were calculated at the individual level. Weights were calibrated
to regional population estimates by age and sex, and then normalized to
the total sample size.14 Weighting was carried out in
R using the glm, anesrake, and survey packages.
Seroprevalence estimation was done in SAS using the SURVEYFREQ procedure
and the calibrated survey weights. Taylor series variance estimation was
used to account for the clustered sample design, treating each survey
site as a separate cluster. Unweighted counts and proportions were also
computed in SAS. The χ2 test was used to assess the
differences in prevalence across demographic characteristics.
We conducted unadjusted and multivariable logistic regression,
incorporating survey weights, to assess the associations between
demographic and behavioral characteristics with seropositivity. The
analysis included participants with complete age and sex data. Final
multivariable models included variables with p<0.05 and
variables (sex, age, residence, region, number of household members,
comorbid conditions, and history of COVID-19, travel) chosen a
priori based on their likely association with the risk of SARS-CoV-2
past infection.
Regional-level seroprevalence estimates were applied to 2020
region-specific population projections from the Cameroon Statistics
Agency to estimate the total number of SARS-CoV-2 infections in each
region that had occurred in the survey period (October-December 2020).
These numbers were compared with the total number of reported cases in
the country at the end of the study (December 2020) to estimate the
ratio of reported cases to total SARS-CoV-2 infections.
Agreement in test results between
the WANTAI and Abbott assays was also evaluated using kappa statistics.