Soldiers almost always eat their meals in large dining facilities. Hundreds - even thousands - of soldiers may partake of a single meal. This puts them at risk for common source infection with gastrointestinal pathogens, such as Shigella, Salmonella, enterotoxigenic E. coli, and hepatitis A virus. Soldiers tend to be of an age when they are particularly active sexually, and sexually transmitted diseases (STD’s) are a significant source of morbidity in certain armies. Living conditions in the barracks put soldiers at risk for person-to-person transmission of infectious diseases such as meningococcal meningitis, influenza, and measles. Deployment to tropical regions may involve morbidity due to malaria, Leishmaniasis, and yellow fever.