Most of the detected gastrointestinal disease outbreaks associated with cruise ships have been linked to food or water consumed on board. Factors that have contributed to outbreaks include contaminated bunkered water, inadequate disinfection of water, potable water contaminated by sewage on ship, poor design and construction of storage tanks for potable water, deficiencies in food handling, preparation and cooking, and use of seawater in the galley.
Norovirus is the most common pathogen implicated in outbreaks. Symptoms often start with sudden onset of vomiting and/or diarrhoea. There may be fever, abdominal cramps and malaise. The virus can spread in food or water or from person to person; it is highly infectious and in an outbreak on a cruise ship, more than 80% of the passengers can be affected. To prevent or reduce outbreaks of gastroenteritis caused by norovirus, ships are enhancing food and water sanitation measures and disinfection of surfaces; more ships are providing hand gel dispensers at strategic locations throughout the ship and passengers and crew are urged to use them. Some cruise companies ask that those who present with gastrointestinal symptoms at on-board medical centres be put into isolation until at least 24 h after their last symptoms, and some ships also isolate asymptomatic contacts for 24 h.
Influenza and other respiratory tract infections
Respiratory tract infections are frequent among cruise ship passengers. Travellers from areas of the world where influenza viruses are in seasonal circulation may introduce such viruses to regions of the world where influenza is not in seasonal circulation. Crew members who serve passengers may become reservoirs for influenza infection and may transmit disease to passengers on subsequent cruises.
Legionellosis (Legionnaires’ disease) is a potentially fatal form of pneumonia, first recognized in 1976. The disease is normally contracted by inhaling Legionella bacteria deep into the lungs. Legionella species can be found in tiny droplets of water (aerosols) or in droplet nuclei (the particles left after water has evaporated). More than 50 incidents of legionellosis, involving over 200 cases, have been associated with ships during the past three decades. For example, an outbreak of legionellosis occurring on a cruise ship in 1994, resulted in 50 passengers on nine other cruises becoming infected, with one death. The disease was linked to a whirlpool spa on the ship. Other sources have been potable water supplies and exposure during port layovers.
Prevention and control depend on proper disinfection, filtration and storage of source water, and on designing piping systems without dead ends. Regular cleaning and disinfection of spas are required to reduce the risk of legionellosis on ships.
Other communicable diseases
The outbreaks of varicella and rubella that have occurred underscore the need for travellers to make sure that they are up to date with routine vaccinations; major cruise ship companies are requesting that their crews be vaccinated against varicella and rubella.