Vector densities that potentiate Dengue outbreaks in a Brazilian city

To identify the critical vector density that potentiates dengue outbreaks i n an endemic site and to identify obstacles to anti-dengue activities, we c orrelated a series of dengue outbreaks in a Brazilian city with the intensi ty 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 o f 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 rou tine anti-vector activities. One dengue outbreak became apparent to authori ties more than two months after it commenced but would have been identified almost immediately had dengue-like disease in indicator hospitals been mon itored. 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 o utbreaks of dengue.