Abstract:
Background
Insecticide-treated nets are the cornerstone of global malaria control and have been shown
to reduce malaria morbidity by 50–60%. However, some areas are experiencing a resur-
gence in malaria following successful control. We describe an efficacy decay framework to
understand why high malaria burden persists even under high ITN coverage in a community
in western Kenya.
Methods
We enrolled 442 children hospitalized with malaria and paired them with age, time, village
and gender-matched controls. We completed comprehensive household and neighborhood
assessments including entomological surveillance. The indicators are grouped into five
domains in an efficacy decay framework: ITN ownership, compliance, physical integrity,
vector susceptibility and facilitating factors. After variable selection, case-control data were
analyzed using conditional logistic regression models and mosquito data were analyzed
using negative binomial regression. Predictive margins were calculated from logistic regres-
sion models.
Results
Measures of ITN coverage and physical integrity were not correlated with hospitalized
malaria in our study. However, consistent ITN use (Adjusted Odds Ratio (AOR) = 0.23, 95%
CI: 0.12–0.43), presence of nearby larval sites (AOR = 1.137, 95%CI: 1.02–1.27), and spe-
cific types of crops (AOR (grains) = 0.446, 95%CI: 0.24–0.82) were significantly correlated with malaria amongst children who owned an ITN. The odds of hospitalization for febrile
malaria nearly tripled when one other household member had symptomatic malaria infec-
tion (AOR–2.76, 95%CI:1.83–4.18). Overall, perfect household adherence could reduce
the probability of hospitalization for malaria to less than 30% (95%CI:0.12–0.46) and adjust-
ing environmental factors such as elimination of larval sites and growing grains nearby
could reduce the probability of hospitalization for malaria to less than 20% (95%CI:0.04–
0.31).
Conclusion
Availability of ITNs is not the bottleneck for malaria prevention in this community. Behavior
change interventions to improve compliance and environmental management of mosquito
breeding habitats may greatly enhance ITN efficacy. A better understanding of the relation-
ship between agriculture and mosquito survival and feeding success is needed.
