BACKGROUND : It is widely acknowledged that modifications to existing control interventions are required if South
Africa is to achieve malaria elimination. Targeting indoor residual spraying (IRS) to areas where cases have been
detected is one strategy currently under investigation in northeastern South Africa. This seroprevalence baseline
study, nested within a targeted IRS trial, was undertaken to provide insights into malaria transmission dynamics in
South Africa and evaluate whether sero-epidemiological practices have the potential to be routinely incorporated
into elimination programmes.
METHODS : Filter-paper blood spots, demographic and household survey data were collected from 2710 randomly
selected households in 56 study wards located in the municipalities of Ba-Phalaborwa and Bushbuckridge. Blood
spots were assayed for Plasmodium falciparum apical membrane antigen-1 and merozoite surface protein-119 bloodstage
antigens using an enzyme linked immunosorbent assay. Seroprevalence data were analysed using a reverse
catalytic model to determine malaria seroconversion rates (SCR). Geospatial cluster analysis was used to investigate
transmission heterogeneity while random effects logistic regression identified risk factors associated with malaria
RESULTS : The overall SCR across the entire study site was 0.012 (95% CI 0.008–0.017) per year. Contrasting SCRs, corresponding
to distinct geographical regions across the study site, ranging from <0.001 (95% CI <0.001–0.005) to 0.022
(95% CI 0.008–0.062) per annum revealed prominent transmission heterogeneity. Geospatial cluster analysis of household
seroprevalence and age-adjusted antibody responses detected statistically significant (p < 0.05) spatial clusters
of P. falciparum exposure. Formal secondary education was associated with lower malaria exposure in the sampled
population (AOR 0.72, 95% CI 0.56–0.95, p = 0.018).
CONCLUSIONS : Although overall transmission intensity and exposure to malaria was low across both study sites,
malaria transmission intensity was highly heterogeneous and associated with low socio-economic status in the
region. Findings suggest focal targeting of interventions has the potential to be an appropriate strategy to deploy
in South Africa. Furthermore, routinely incorporating sero-epidemiological practices into elimination programmes may prove useful in monitoring malaria transmission intensity in South Africa, and other countries striving for malaria
Additional file 1. Box plots of antibody responses, in the form of optical
density (OD) values, for both PfAMA-1 and PfMSP-119 among different
ages/age bands across the entire study site. Hollow black circles represent
outlier OD responses. Red lines correspond to seropositive cut-offs, which
equate to 0.067 for PfAMA-1 and 0.103 for PfMSP-119.
Additional file 2. Age-seroprevalence to either PfAMA-1 or PfMSP-119
among sampled participants of both Ba-Phalaborwa and Bushbuckridge.
Red triangles: observed age-seroprevalence; solid lines: predicted seroprevalence;
dotted lines: predicted seroprevalence upper and lower 95%
Additional file 3. Demographic and risk factors associated with seroprevalence
to either PfAMA-1 and PfMSP-119.