Urban heat island intensity and chikungunya incidence: a multi-city time-series analysis in Brazil

OBJECTIVES: Urban heat islands (UHIs) produce 2°C-8°C in urban cores excesses, accelerating Aedes aegypti development and shortening chikungunya virus (CHIKV) extrinsic incubation, yet UHI intensity's (UHII) independent contribution to CHIKV transmission remanins unquantified. METHODS: We conducted an ecological time-series analysis of five Brazilian cities (2015-24; n = 563 city-months) . Monthly UHII was derived from MODIS land surface temperature (urban-core minus peri-urban) via Google Earth Engine; CHIKV incidence came from InfoDengue. Lag-specific (0-3 months) Poisson generalized linear models were adjusted for temperature, humidity, and seasonality. Given severe overdispersion, quasi-Poisson and negative-binomial models were the preferred sensitivity analyses. RESULTS: Across 261 353 cases, each 1°C UHII increase was associated with higher lag-1 incidence in subtropical Rio de Janeiro (RR = 2.857, 95% CI 2.799-2.915) and Salvador (RR = 1.168, 1.156-1.179; both P < .001). Brasília showed inverse associations (lags 0-3), Fortaleza (highest burden, 133 371 cases) a mixed lag pattern, and São Paulo minimal effects despite the highest UHII. Incidence peaked in April-May. CONCLUSIONS: UHII-CHIKV associations were heterogeneous; city-specific thermal context should inform integrating satellite-derived heat metrics into arboviral surveillance, as several associations attenuated or lost statistical significance under overdispersion-robust models and were sensitive to individual epidemic years.