Relating household entomological measures to individual malaria risk

The gold standard measure of malaria exposure is the entomological inoculation rate (EIR), or the number of infectious bites an individual receives over a given period. Nevertheless, it is unclear whether household EIR reflects heterogeneity in individual infection risk.

To investigate this relationship, we used data collected from a cohort of 439 children aged 0.5-5 years in 239 households from 2011-2017 in three Ugandan districts: low-EIR Jinja, intermediate-EIR Kanungu and high-EIR Tororo. Participants underwent passive and quarterly active surveillance for clinical malaria, defined as fever with positive thick blood smear. Monthly vector densities and sporozoite rates in participating households were estimated using CDC light traps. We assessed the association between spatiotemporally smoothed household log₂-transformed EIR and individual malaria incidence using Poisson generalized additive mixed effects models.

Comparison across sites suggested an increasing relationship between average EIR and malaria incidence. Within-site relationships, however, varied by site, with a positive association in Kanungu (incidence rate ratio [IRR] 1.09, 95% credible interval 1.04-1.14) but none in Jinja (1.02, 0.774-1.26) or Tororo (1.02, 0.986-1.06).

These results show the relationship between measured EIR and malaria incidence may depend on local transmission dynamics and be strongest at intermediate EIR, while underscoring the challenges of using household-level measures of exposure.