Data from: The impact of hotspot-targeted interventions on malaria transmission in Rachuonyo south district in the western Kenyan highlands: a cluster-randomized controlled trial

Background: Malaria transmission is highly heterogeneous, generating
malaria hotspots that can fuel malaria transmission across a wider area.
Targeting hotspots may represent an efficacious strategy for reducing
malaria transmission. We determined the impact of interventions targeted
to serologically defined malaria hotspots on malaria transmission both
inside hotspots and in surrounding communities. Methods and Findings:
Twenty-seven serologically defined malaria hotspots were detected in a
survey conducted from 24 June to 31 July 2011 that included 17,503
individuals from 3,213 compounds in a 100-km2 area in Rachuonyo South
District, Kenya. In a cluster-randomized trial from 22 March to 15 April
2012, we randomly allocated five clusters to hotspot-targeted
interventions with larviciding, distribution of long-lasting
insecticide-treated nets, indoor residual spraying, and focal mass drug
administration (2,082 individuals in 432 compounds); five control clusters
received malaria control following Kenyan national policy (2,468
individuals in 512 compounds). Our primary outcome measure was parasite
prevalence in evaluation zones up to 500 m outside hotspots, determined by
nested PCR (nPCR) at baseline and 8 wk (16 June–6 July 2012) and 16 wk (21
August–10 September 2012) post-intervention by technicians blinded to the
intervention arm. Secondary outcome measures were parasite prevalence
inside hotpots, parasite prevalence in the evaluation zone as a function
of distance from the hotspot boundary, Anopheles mosquito density,
mosquito breeding site productivity, malaria incidence by passive case
detection, and the safety and acceptability of the interventions.
Intervention coverage exceeded 87% for all interventions. Hotspot-targeted
interventions did not result in a change in nPCR parasite prevalence
outside hotspot boundaries (p ≥ 0.187). We observed an average reduction
in nPCR parasite prevalence of 10.2% (95% CI −1.3 to 21.7%) inside
hotspots 8 wk post-intervention that was statistically significant after
adjustment for covariates (p = 0.024), but not 16 wk post-intervention (p
= 0.265). We observed no statistically significant trend in the effect of
the intervention on nPCR parasite prevalence in the evaluation zone in
relation to distance from the hotspot boundary 8 wk (p = 0.27) or 16 wk
post-intervention (p = 0.75). Thirty-six patients with clinical malaria
confirmed by rapid diagnostic test could be located to intervention or
control clusters, with no apparent difference between the study arms. In
intervention clusters we caught an average of 1.14 female anophelines
inside hotspots and 0.47 in evaluation zones; in control clusters we
caught an average of 0.90 female anophelines inside hotspots and 0.50 in
evaluation zones, with no apparent difference between study arms. Our
trial was not powered to detect subtle effects of hotspot-targeted
interventions nor designed to detect effects of interventions over
multiple transmission seasons. Conclusions: Despite high coverage, the
impact of interventions targeting malaria vectors and human infections on
nPCR parasite prevalence was modest, transient, and restricted to the
targeted hotspot areas. Our findings suggest that transmission may not
primarily occur from hotspots to the surrounding areas and that areas with
highly heterogeneous but widespread malaria transmission may currently
benefit most from an untargeted community-wide approach. Hotspot-targeted
approaches may have more validity in settings where human settlement is
more nuclear. Trial registration: ClinicalTrials.gov NCT01575613.