Spatial Patterns of Dengue Incidence in Nepal During Record Outbreaks in 2022 and 2023: Implications for Public Health Interventions.

Abstract

Dengue, which was first reported as a travel case in Nepal in 2004, was initially confined to the lower plains but has spread to higher elevations. Large outbreaks in 2022 and 2023 (54,784 and 51,243 cases, respectively), reached every district (n = 77). We calculated the district-wise incidence for 2022 and 2023 by digitizing case data from Nepal's Ministry of Health and Population and 2021 census data from the National Statistics Office. The incidence and peak incidence months for each year were mapped, and spatial clusters (hotspots and cold spots) and outliers of incidence rates were identified using Local Moran's I. In 2022, district-wise peak cases occurred from August to October. One hotspot (high-high cluster), with high values surrounded by high-value neighbors, including six districts around Kathmandu, and one cold spot (low-low cluster), with low values surrounded by low-value neighbors, comprising eight high-elevation districts in Nepal's northwest region were identified. In 2023, cases peaked from March to November, indicating more distributed peaks that started earlier; hotspots shifted to the north-central and eastern regions, and a low-high outlier district in the central region was identified. Identifying the timing of peaks and spatial clusters of dengue incidence can inform targeted management, thereby improving effectiveness and cost-efficiency. A baseline examination of recent dengue incidence in Nepal, highlighting timing and spatial clustering in incidence, is provided in this study. The mountainous northwest cold spots align with expectations of fewer mosquitoes because of the geography and climate. However, the 2022 dengue incidence peaked across all 77 districts in 3 months, suggesting that ecological and climatic factors may no longer be effective barriers.