Risk factors associated with an outbreak of dengue fever in a favela in Fortaleza, north-east Brazil

To increase the effectiveness of ongoing anti-dengue control measures, we c onducted a case-control study in a favela in Fortaleza (north-east Brazil) during an outbreak of dengue fever. Cases were defined according to the nat ional guidelines for dengue control as well as based on the detection of Ig M-dengue antibodies, and 34 cases and 34 controls were investigated. Signif icant risk factors were: living in a street perpendicular to the beach on w hich the favela is situated (P < 0.0001), an interval > 30 days since the l ast visit of the vector control agent (P = 0.001), receptacles in the garde n or courtyard (P = 0.001), plants with temporary water pools on the proper ty, gutter to collect rainwater, uncovered water storage container (all P = 0.02), and no waste collection (P = 0.03). Socio-economic variables were n ot associated with dengue fever. The probable starting point of the epidemi c was an uncovered water tank on the roof of the house adjacent to the inde x case. From there, the outbreak spread uphill parallel to the prevailing d irection of the wind. Thus, the chronological and spatial evolution of the epidemic could have been forecast after the first cases had occurred. This example of investigative epidemiology in an operational setting shows that targeted intervention leading to increased effectiveness of control measure s is possible.