Abstract
Chagas disease vector control campaigns are being conducted in Latin America, but little is known about medium-term or long-term effectiveness of these efforts, especially in urban areas. After analyzing entomologic data for 56,491 households during the treatment phase of a Triatoma infestans bug control campaign in Arequipa, Peru, during 2003-2011, we estimated that 97.1% of residual infestations are attributable to untreated households. Multivariate models for the surveillance phase of the campaign obtained during 2009-2012 confirm that nonparticipation in the initial treatment phase is a major risk factor (odds ratio [OR] 21.5, 95% CI 3.35-138). Infestation during surveillance also increased over time (OR 1.55, 95% CI 1.15-2.09 per year). In addition, we observed a negative interaction between nonparticipation and time (OR 0.73, 95% CI 0.53-0.99), suggesting that recolonization by vectors progressively dilutes risk associated with nonparticipation. Although the treatment phase was effective, recolonization in untreated households threatens the long-term success of vector control.
Highlights
We computed the residual infestation for each iteration of the Monte Carlo Markov Chain (MCMC) and generated the distribution and credible interval at 95% of the residual population size for each category of participation (Table S2)
As the prevalence in households treated only the second time is 5 times lower than in households participating in both treatments, we consider the extreme case where the prevalence in non-participating households is 5 times lower than in households participating only in the second treatment. Even this strong modification does not qualitatively change our results: over 85% of the residual infestation is still in non-participating households, and the overall effectiveness of the treatment phase would be even higher with a decrease of 78% of the number of households presenting some residual infestation after the treatment phase (Table S3, fourth column)
To estimate the residual infestation post-treatment in the difference-in-difference framework, we use the results of the difference-in-difference model and extrapolate them to households not observed during the pre-treatment survey or the second phase of treatment
Summary
The treatment phase used pyrethroid insecticides, mainly deltamethrin (96.4%), in 5 formulations over the 9 years of the treatment covered here (Tab. S1). The formulation was diluted in water and applied, using a Hudson X-Pert compression sprayer at a target dose rate of 30 mg/m2 for deltamethrin based insecticides and 36 mg/m2 for lambda-cyhalothrin based insecticides. OTHRINE 50 SC: suspension concentrate of deltamethrin. K-OTHRINE 5% PM: wettable powder of deltamethrin. LAMBDA 10% PM: wettable powder of lambda-cyhalothrin. DEMAND 10 CS: capsule suspension of lambda-cyhalothrin
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