Incidence and risk factors for disease and non-battle injury aboard the hospital ship USNS COMFORT during a Humanitarian Assistance and Disaster Response Mission, Continuing Promise 2011

Background: Disease and non-battle injury (DNBI) are a leading cause of morbidity in deployments and can compromise operational mission performance. No study to date has examined DNBI incidence and impact aboard humanitarian aid/disaster response (HADR) mission ships. Methods: From April to September 2011, US military and civilian personnel participated in Continuing Promise 2011, a HADR training mission aboard USNS COMFORT (T-AH 20). Health surveillance was conducted for the purpose of assessing DNBI trends and improving force health protection during the deployment through passive surveillance, collection of DNBI data among those seeking care at the ship's clinic, and actively through use of an anonymous weekly, self-report questionnaire. Categorical and total DNBI incidence rates were calculated per 100 person-weeks and incidence rate ratios (IRR) were calculated utilizing a negative binomial model to assess potential risk factors. Results: The leading syndrome-specific cause of weekly visits to the ship's clinic was gastrointestinal (GI) followed by dermatologic and respiratory conditions (2.22, 1.97, and 1.46 cases per 100 person-weeks, respectively). The top three categorical DNBI were similarly represented by the questionnaire, with respiratory conditions having the highest reported rate followed by dermatologic and GI (11.79, 8.71, and 7.38 cases per 100 person-weeks, respectively). GI had the highest morbidity measures accounting for 61.9 % of lost work days and 27.3 % of reported moderate/severe impact to mission performance. Several factors were also associated with increased DNBI rates including personnel ages 26-36 (IRR = 1.23), officers (IRR = 1.23), days-off-ship (IRR = 1.09), and affiliation with nursing services (IRR = 1.48), naval mobile construction battalion (IRR = 3.17), and security (IRR = 1.71). Conclusions: DNBI can significantly impact mission performance on HADR missions, and establishing baseline rates and identifying risk factors can help improve force health protection in future HADR missions.