Multiple enteropathogenic viruses in a gastroenteritis outbreak in a military exercise of the Portuguese Army

Background: Gastroenteritis is one of the most common infectious diseases in the military populations and can diminish operational effectiveness and impede force readiness. Objectives: The present study investigates the cause and the source of an acute gastroenteritis outbreak that occurred during a military exercise of the Portuguese Army, in February 2013. Study Design: A retrospective investigation was performed and stool samples, food items and water were screened for common foodborne bacteria and viruses, namely Norovirus GI, Norovirus GII, Astrovirus, Rotavirus, Adenovirus and Sapovirus. Results: From the total of 160 soldiers that participated in the military exercise 20 developed gastroenteritis (attack rate of 12.5%). Symptoms were predominantly vomiting (n = 17, 85%) and diarrhoea (n = 9, 45%). The first cases occurred 24–48 h after drinking water from the creek, the plausible origin of the outbreak. The epidemic peak was registered 2 days after and the last cases 6 days after, upon returning to base. No pathogenic bacteria were found in stools however virological analysis revealed the presence of multiple enteropathogenic viruses, namely Norovirus GI (GI.3), Norovirus GII (GII.4 New Orleans 2009), Astrovirus and Sapovirus, as single or co-infections. Food and water samples were not tested for the presence of viruses due to exhaustion of samples on bacteriological analysis. Conclusions: To the best of our knowledge this is the first report of a viral gastroenteritis outbreak among military personnel in the Portuguese Army