Outdoor spatial spraying against dengue: A false sense of security among inhabitants of Hermosillo, Mexico

BACKGROUND Government-administered adulticiding is frequently conducted in response to dengue transmission worldwide. Anecdotal evidence suggests that spraying may create a "false sense of security" for residents. Our objective was to determine if there was an association between residents' reporting outdoor spatial insecticide spraying as way to prevent dengue transmission and both their reported frequency of dengue prevention practices and household entomological indices in Hermosillo, Mexico. METHODOLOGY/PRINCIPAL FINDINGS A non-probabilistic survey of 400 households was conducted in August 2014. An oral questionnaire was administered to an adult resident and the outer premises of the home were inspected for water-holding containers and presence of Ae. aegypti larvae and pupae. Self-reported frequency of prevention practices were assessed among residents who reported outdoor spatial spraying as a strategy to prevent dengue (n = 93) and those who did not (n = 307). Mixed effects negative binomial regression was used to assess associations between resident's reporting spraying as a means to prevent dengue and container indices. Mixed effects logistic regression was used to determine associations with presence/absence of larvae and pupae. Those reporting spatial spraying disposed of trash less frequently and spent less time indoors to avoid mosquitoes. They also used insecticides and larvicides more often and covered their water containers more frequently. Their backyards had more containers positive for Ae. aegypti (RR = 1.92) and there was a higher probability of finding one or more Ae. aegypti pupae (OR = 2.20). Survey respondents that reported spatial spraying prevented dengue were more likely to be older and were exposed to fewer media sources regarding prevention. CONCLUSIONS/SIGNIFICANCE The results suggest that the perception that outdoor spatial spraying prevents dengue is associated with lower adoption of prevention practices and higher entomological risk. This provides some support to the hypothesis that spraying may lead to a "false sense of security". Further investigations to clarify this relationship should be conducted. Government campaigns should emphasize the difficulty in controlling Ae. aegypti mosquitoes and the need for both government and community action to minimize risk of dengue transmission.