Local thermal anomalies and the altitudinal rise of dengue hospitalisation rates in Ecuador, 2011–2024: a national ecological study

Abstract

Introduction Dengue is expanding beyond its traditional lowland range as rising temperatures may enable Aedes aegypti establishment at progressively higher altitudes. Ecuador, spanning sea level to above 4500 m, offers a natural altitudinal experiment, yet hospital-based evidence on the thermal drivers of Andean dengue is lacking. Methods We conducted a national ecological time-series analysis at the canton level using Ecuador's hospital discharge registry (INEC) for 2011–2024, the period with standardised canton coding, identifying dengue hospitalisations by ICD-10 codes A90, A91 and A97. Monthly land surface temperature, precipitation and vegetation index were derived from MODIS and GPM products. A distributed lag non-linear model estimated the temperature–hospitalisation association; a quasi-Poisson model restricted to Andean cantons (≥1500 m), with canton, calendar-month and year fixed effects, tested whether thermal anomalies above each canton's 2007–2015 baseline were associated with hospitalisation rates. Results Among 74,601 dengue hospitalisations with a resolvable canton of residence (232 deaths; case fatality 0.31%), dengue was recorded in 68 cantons above 1500 m, including altitudes exceeding 3000 m. The national hospitalisation rate rose from 29.7 to 77.0 per 100,000 and the Andean rate approximately 7-fold (1.9 to 12.8). The minimum hospitalisation temperature was 18.4°C nationally and 18.9°C in Andean cantons. A +1°C anomaly versus zero was associated with a 1.07-fold increase in hospitalisation rates (95% CI 1.02–1.13; p = 0.012). Without canton fixed effects, the same contrast yielded 1.21 (1.07–1.36); the within-canton association fell to 1.04 (1.00–1.08) when the 2024 epidemic year was excluded. Discussion Positive deviations from local historical baselines, rather than absolute temperature, were associated with rising dengue hospitalisation rates among Andean residents, by a modest margin that depends materially on the 2023–2024 epidemic. In-hospital case fatality was nearly twice as high in low Andean cantons (0.62%, 95% CI 0.20–1.45; five deaths) as on the coast (0.33%), a non-significant difference that nonetheless supports strengthening dengue recognition in highland facilities.