Influenza Surveillance on Cruise Ships

Acute respiratory illness, ranging from the common cold to the influenza virus, affects people worldwide. In the U.S., roughly 3000–49,000 people die annually because of complications from influenza. Acute respiratory illness is common among international travelers. Respiratory illness is specifically problematic on cruise ships, estimated at approximately 27% of all recorded illnesses. The spread of influenza on cruise ships is a particular problem for several reasons. First, the grouping of several thousand people on board for a week or more allows considerable mixing of infected and susceptible individuals. Second, itineraries often involve travel to tropical or semitropical destinations, where influenza may circulate year round. Third, crew members can be a source of continuing infection for new passenger cohorts as infections may remain on board from one cruise to the next. The popularity of cruise ship travel has been growing over the last decade. The Cruise Lines International Association reports that the average annual passenger growth from 1990 to 2010 was 7.6%. With passengers and crew coming together from all over the world, the potential for influenza transmission, with significant morbidity, is substantial. However, little attention has been given to routine influenza surveillance on cruise ships. Influenza outbreaks on cruise ships have occurred worldwide and during all months of the year. Both passengers and crew members are affected, and many documented outbreaks occurred outside the domestic influenza season. Reported attack rates range from 3.8% to 37%. Previous outbreaks have resulted mainly from the importation of influenza from a community in which it was circulating, with subsequent prolonged person-to-person spread aboard the ship. Recommendations included the establishment of an acute respiratory infection surveillance system to allow timely interventions that are efficient and effective. Miller and colleagues reported that control measures such as isolation of cases and treatment with antivirals can work,