Climate drivers and winter constraints of dengue epidemics: a 10-year epidemiological perspective study in the Lao People's Democratic Republic

Abstract

BackgroundDengue fever is hyperendemic in the Lao People's Democratic Republic (PDR), where transmission is driven by Aedes mosquitoes and influenced by large-scale climatic phenomena, including the El Ni & ntilde;o-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). As a landlocked nation, the Lao PDR experiences sharper winter temperature declines than coastal regions, which may impose a seasonal "bottleneck" on vector survival and dengue transmission. This study examined whether winter minimum temperatures act as a seasonal transmission bottleneck, alongside the Oceanic Ni & ntilde;o Index (ONI) and the Dipole Mode Index (DMI), during 2014-2023.MethodsMonthly dengue case counts reported to the National Center for Laboratory and Epidemiology, Ministry of Health, Lao PDR, from January 2014 to December 2023 were analyzed using region-specific quasi-Poisson distributed lag nonlinear models. Models incorporated 3-month-lagged ONI/DMI cross-basis functions, winter minimum temperature hinges, long-term trends, and seasonality, with population as an offset. Region-specific estimates were pooled using multivariate meta-analysis to generate best linear unbiased predictions (BLUPs). Optimal lag structures and temperature thresholds were selected by minimizing the quasi-Akaike information criterion and residual sum of squares.ResultsA total of 134,093 dengue cases were reported, with substantial regional heterogeneity. The Capital Region had the highest burden (40,672 cases; annual incidence 35.4 per 100,000), followed by the Southern Mountains and Tropical Rainforests region (20,176 cases; 23.3 per 100,000). Annual incidence in each region appeared constrained by region-specific winter minimum temperature thresholds. Pooled BLUPs analyses adjusted for covariates revealed monotonic cumulative relative risk increases with ONI [RR = 2.83 at ONI = 2.0; 95% confidence interval (CI): 1.46-5.49) and decreases with DMI (RR = 0.37 at DMI = 1.5; 95% CI: 0.24-0.59).ConclusionsWinter cold functions as a primary bottleneck for dengue transmission in the Lao PDR, with ENSO amplifying and IOD suppressing outbreak risk. These findings support the development of climate-integrated, region-specific early warning systems. Incorporating 3-month-lagged climate indices may enhance public health preparedness for future dengue outbreaks.