Risk factors of imported malaria in Bhutan: A retrospective analysis (2013-2024)

Bhutan's malaria elimination is constrained by imported malaria. Hence, this study aimed to quantify the risk factors of imported malaria in Bhutan.

Individual malaria data for the period 2013 - 2024 were obtained from the Bhutan National Malaria Control Programme. Seasonal trend decomposition and hotspot analysis were conducted to explore trends and high-risk areas of imported malaria. Multivariable Bayesian logistic regression was used to quantify risk factors of imported malaria.

Imported malaria made up 81% (563/693) of total cases and 61.8% (348) originated from India. Imported malaria did not show significant trend; however, hotspots were observed in major points of entry, in the capital city, and at hydropower projects sites. Malaria cases recorded after 2018 were eight times (adjusted odds ratio [AOR]= 8.0 (95% credible interval [CrI] 4.9 - 13.0) more at odds of being imported than those reported before 2018. Districts without borders with India had higher odds of reporting imported malaria (AOR 4.4, 95% CrI 1.2 - 24.7) compared to districts sharing a border with India. Labourers (AOR = 38.1; 95% CrI 10.5 - 187.1) and military personnel (AOR = 5.0; 95% CrI 1.5 - 20.3) were 38 and five times more likely of being imported malaria compared to public servants.

The imported malaria poses significant threat to national elimination plan. The interior non-border districts, migrant labourers and security force personnels were significantly associated with increased odds of imported malaria. Therefore, surveillance and response strategies should be targeted to these hotspots and hotpops to reduce importation risks and sustain malaria-free status.