Malaria Incidence in U.S. Military Families is Related to Service Member's Birthplace

Background Foreign-born persons make up approximately 5% of the U.S. military active duty service members. Studies in the general population show travelers visiting friends and relatives have an increased risk of malaria acquisition. We hypothesized a higher incidence of malaria within the Military Health System (MHS) for those with a familial connection to malaria-endemic countries. Methods We performed a retrospective cohort study of all service members and their family members enrolled in the MHS between October 2012 and September 2018. Participants were allocated into two groups according to the service member’s country of birth: malaria-endemic country or non-endemic country. Malaria cases were identified by ICD code and annual incidence rates were calculated based on service member’s birth world region. Incidence rate ratios (IRR) compared the two groups. Results 281 cases of malaria were identified during the six-year study period. The malaria-endemic group (n=67) had five times the risk of malaria than the non-endemic group (n=214) (IRR 5.2, 95% CI 2.4-10.4). Incidence remained higher for the malaria-endemic group even when stratified by service member and family member status. Those connected to the sub-Saharan Africa region had an average annual incidence rate of 42 cases per 100,000-persons, accounting for 86.6% of all malaria-endemic cases. Only 48% of all cases sought pre-travel medical counseling. Conclusions There was over five times higher incidence of malaria in the malaria-endemic group, highlighting their increased incidence of travel-related infectious diseases despite universal health insurance coverage and access to pre-travel medical care.