Vector densities that potentiate dengue outbreaks in a Brazilian city.

TLDR

The study aimed to determine the vector density threshold that triggers dengue outbreaks and to uncover barriers to anti‑dengue efforts in a Brazilian city. Researchers correlated dengue outbreak incidence with the intensity of anti‑vector source‑reduction activities. House infestation rates were inversely related to intervention intensity, vector populations were independent of rainfall, drought increased breeding through stored water and diverted health workers, delayed outbreak detection highlighted the need for active surveillance, and maintaining infestation below 1 % of houses effectively prevented outbreaks.

Abstract

To identify the critical vector density that potentiates dengue outbreaks in an endemic site and to identify obstacles to anti-dengue activities, we correlated a series of dengue outbreaks in a Brazilian city with the intensity of its anti-vector source-reduction activities. The proportion of houses infested by vector mosquitoes correlated inversely with intensity of anti-mosquito interventions, and the vector population developed independently of rainfall. Local periods of drought promoted vector abundance in two ways: residents stored water in which vector mosquitoes could breed, and cholera outbreaks due to contaminated water diverted local health workers from routine anti-vector activities. One dengue outbreak became apparent to authorities more than two months after it commenced but would have been identified almost immediately had dengue-like disease in indicator hospitals been monitored. Active surveillance, therefore, offers a window of opportunity for promptly executed anti-dengue interventions. Source-reduction measures that suppress vector infestations to less than 1% of houses effectively avert outbreaks of dengue.