Background: The European Union Training Mission Mali（EUTM MLI） is a multinational military training deployment to the Western African tropical nation of Mali. Based on routinely collected disease and non-battle injury surveillance data

this study quantifies the true impact of infectious diseases for this tropical mission and potential seasonal variations in infectious disease threats.Methods: Categorized health events during the EUTM MLI mission and associated lost working days were reported using the EpiNATO-2 report. Infection-related health events were descriptively analyzed for a 4-year period from the 12 th week in 2013 to the 13 th week in 2017. Aggregated EpiNATO-2 data collected from all missions other than EUTM MLI were used as a comparator.Results: Among the infectious diseases reported by EUTM MLI

non-severe upper respiratory infections and gastrointestinal diseases dominated quantitatively

accounting for 1.65 and 1.42 consultations per 100 person-weeks

respectively. The number of recorded infectious disease-associated lost working days during the whole study interval was 723. Seasonal changes in disease frequency were detectable. More gastrointestinal infections were seen in the rainy season

and more respiratory infections occurred in the dry season; these were associated with peaks of more than 2.5 consultations per 100 person-weeks for both categories.Conclusion: Despite initial concerns focused on tropical infectious diseases during this mission in tropical Mali

upper respiratory tract and gastrointestinal infections predominate. The relatively low number of reported lost working days may indicate that these infections are at the milder end of the spectrum of infectious diseases despite a likely reporting bias.