Postdeployment Plasmodium Infections among South Korean Soldiers Receiving Mefloquine Chemoprophylaxis in South Sudan.

Postdeployment Plasmodium infection continues to occur despite recommended chemoprophylaxis among military personnel and long-term travelers deployed to malaria-endemic regions. We evaluated factors associated with postdeployment Plasmodium infection among South Korean soldiers receiving weekly mefloquine chemoprophylaxis during prolonged deployment to South Sudan. We conducted a retrospective study of 42 soldiers from a military unit who completed a standardized 40-week deployment to South Sudan between 2020 and 2023. All personnel were prescribed weekly mefloquine throughout deployment and 4 weeks after departure and reported completing the regimen. Postdeployment Plasmodium infection was defined as laboratory-confirmed Plasmodium infection detected after return from deployment despite completion of chemoprophylaxis. Demographic, anthropometric, clinical, and laboratory data were obtained from medical records. Nine soldiers developed postdeployment Plasmodium infection (21.4%), of whom six had Plasmodium ovale and three had Plasmodium falciparum infection. No severe malaria cases or malaria-related deaths occurred. Median body surface area (BSA) was significantly higher among infected soldiers than controls (2.01 versus 1.90 m2; P = 0.007). In an age-adjusted Firth-penalized logistic regression model, higher BSA was independently associated with postdeployment Plasmodium infection (adjusted odds ratio: 2.55 per 0.1 m2 increase; 95% CI: 1.08-6.06; P = 0.033), whereas body weight showed a borderline association. Postdeployment Plasmodium infection occurred in one-fifth of soldiers despite recommended chemoprophylaxis, highlighting real-world malaria risk during prolonged deployment in highly endemic settings. Higher BSA may contribute to interindividual variability in prophylactic drug exposure. Prospective studies incorporating pharmacokinetic measurements are needed to clarify relationships between body size, drug exposure, and malaria prevention effectiveness.