Malaria situation in a highly endemic province in the Central Highlands of Vietnam: a retrospective analysis

Abstract

Background: Vietnam is progressing towards nationwide malaria elimination by 2030 with residual transmission limited to a few provinces in the Central region including Dak Lak. These areas, especially in the central highlands, continue to have challenges with ongoing forest transmission, movements of vulnerable populations, monitoring and management of imported cases, drug resistance and financial sustainability. This retrospective study aimed to understand the malaria situation in Dak Lak province by describing the characteristics of malaria cases; identifying potential risk factors for Plasmodium falciparum (Pf) and Plasmodium vivax (Pv) infection among reported cases; determining malaria clusters, and the temporal and spatial distributions of these cases between 2017 and 2022. Methods: Monthly district-level passive surveillance data on reported malaria cases from Dak Lak Center for Disease Control were analyzed using logistic regression, time series decomposition, negative binomial time series generalized linear model and spatial analyses. Results: Over the 6-year period, there were 2147 malaria cases reported in Dak Lak province, of which 58.2% were indigenous and 39.1% were imported. Pf was the dominant malaria parasite. Our findings revealed a considerable decline with malaria cases approaching zero since 2021. Malaria infections peaked in the late rainy season in October and November. Temperature and rainfall were most strongly associated with malaria case numbers at positive lags. The number of cases in a given month was highly dependent on the previous month’s cases. Gender, ethnicity, and living in higher endemicity areas were associated with having Pf and Pv infection. There were cold spots in southwest Dak Lak province while no hotspot areas were identified. Conclusions: Despite a dramatic reduction in malaria cases, social behavior change communication and preventive interventions should be maintained, especially for high-risk groups including men, ethnic minorities (H Mông in specific), people living in high transmission risk areas and mobile populations between provinces and across the Vietnam-Cambodia border. These need to be implemented ahead of the peak malaria season. Our findings, along with further operational research, are crucial to guide future elimination plans and resource allocation.