The presence of a vast cohort of individuals in semi-confined settings such as cruise ships, military barracks, and college dormitories is often accompanied by an increase in the risk of particular infections. These are often gastrointestinal infections on cruise ships and respiratory pathogens that are easily transmitted in the barrack and dormitory setting. The control of these infections involves attention to good personal hygiene, safe food and water handling, and use of vaccines to prevent vaccine-preventable diseases.