Illness on Cruise Ships

Transmission of Illness on Cruise Ships

Heightened disease surveillance efforts by cruise lines in cooperation with public health authorities and awareness among cruise ship travelers have led to the detection of illnesses of potential public health significance that might otherwise have gone unnoticed. Communicable diseases occurring onboard cruise ships reflect similar onshore events, but transmission risk may be enhanced by the crowded, semi-enclosed cruise ship environment, with increased opportunities for interpersonal interactions. In addition, an estimated one-third of cruise travelers are senior citizens who, along with travelers with underlying chronic health problems, are at increased risk of morbidity from infectious agents such as Influenza viruses and Legionella. A study of cruise ship medical logs showed that over half of infirmary visits are made by passengers over the age of 65; the most common diagnosis is respiratory tract infection, followed by injuries, nervous system (e.g., seasickness) and GI illness. In recent years, outbreaks of norovirus and influenza have posed particular public health challenges. Outbreaks of influenza A and influenza B can occur among cruise ship passengers and crew year-round worldwide. Previous outbreaks have resulted due to importation of influenza from a community in which it was circulating, with subsequent sustained person-to-person spread on cruise ships. The low infective dose of norovirus, combined with its easy person-to-person transmissibility and ability to survive routine cleaning procedures, has led to large, consecutive cruise outbreaks. Other causes of GI illness clusters on cruise ships have included contaminated food or water due to Salmonella spp., enterotoxigenic Escherichia coli, Shigella spp., Vibrio spp., Staphylococcus aureus, Clostridium perfringens, Cyclospora sp., and Trichinella spirali . The estimated likelihood of contracting gastroenteritis on an average 7-day cruise is less than 1%, and GI illness accounts for fewer than 10% of passenger infirmary visits.

Legionnaires’ disease has led to pneumonia outbreaks on multiple, consecutive cruises. Passengers typically develop symptoms only upon completion of travel, resulting in delayed detection and continuous transmission. Additionally, since cruise travel typically involves stays in hotels as well as multiple environmental exposures during port stops, it is usually difficult to link a cruise ship with infection; however, contamination of ships’ whirlpool spas and potable water supply systems have most commonly been implicated sources. Clusters of rubella and varicella have been investigated on cruises originating in the U.S. and have highlighted the potential of global dissemination of vaccine-preventable diseases through cruise travel. During one investigation, 11% of the crew was shown to be infected with or susceptible to rubella, and 33% of passengers onboard were women of childbearing age, a high-risk group for congenital rubella syndrome if infected during pregnancy. Isolated cases of measles, hepatitis A, typhoid, tuberculosis, meningococcal meningitis have been reported and investigated (unpublished data, CDC Miami Quarantine Station).

Injury and Other Health Considerations for Cruise Ship Travel Injuries are one of the most common reasons for passengers to seek medical care on cruise ships, accounting for about 18% of passenger infirmary visits. As a result of climatic variations, environmental exposure to pollutants, changes in diet and physical activity levels and an increased level of stress due to being in an unfamiliar environment, the cruise ship traveler may be subject to exacerbation of existing chronic health conditions. A prospective cruise ship traveler with health conditions that might increase his or her potential for injury or illness should consult his or her health-care provider before embarking on a cruise. Special cruises are now available for travelers who have certain medical conditions, including those on dialysis.

Gastrointestinal disease

A wide range of pathogens affected passengers and crew during ship-associated gastrointestinal disease outbreaks. These included Vibrio parahaemolyticus, Salmonella species, Hepatitis A, enterotoxigenic Escherichia coli, enterohaemorrhagic Escherichia coli O157, Shigella species, Staphylococcus aureus, Norwalk-like virus (NLV), Cryptosporidium, Giardia lamblia and Cyclospora.
Most of the detected gastrointestinal disease outbreaks were associated with cruise ships and were linked to food or water consumed onboard ship. Factors contributing to outbreaks included contaminated bunkered water, inadequate disinfection of potable water, potable water contaminated by sewage on ship, poor design and construction of potable water storage tanks, deficiencies in food handling, preparation and cooking and use of seawater in the galley.
NLV 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. NLV is a very infectious virus, and, in one outbreak on a cruise ship in 1998, over 80% of the 841 passengers were affected. Outbreaks of acute gastroenteritis are also frequently reported aboard naval ships. One outbreak of viral gastroenteritis on a naval vessel in 1997 affected 1,806 (43%) crewmembers. Another outbreak of a waterborne infection in 1998 affected 200 crew or 22%. These outbreaks cause substantial morbidity among military personnel during deployment. Very little information is available on the incidence of infection among seafarers on general cargo vessels. Many outbreaks and cases of infection probably go undetected. However, inspections on ships carried out in the year 2000 revealed that 9.2% had deficiencies relating to food and catering.

Legionnaires' disease

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 the water has evaporated).
The WHO review showed that over 50 incidents of Legionnaires' disease, involving over 200 cases, were associated with ships in the past three decades.
For example, an outbreak of Legionnaires' disease occurred on a single cruise ship in 1994: 50 passengers were affected on nine different cruises and one passenger died. The disease was linked to a whirlpool spa on the ship.
The problem is not restricted to passenger ships. Surveys carried out on general cargo ships have shown drinking water and air conditioning systems to be contaminated with Legionella pneumophila3.
Serologic surveys of seafarers on cargo ships have also shown that a high proportion have antibodies to Legionella pneumophila, suggesting that those on board ships are at increased risk of legionellosis compared with communities onshore.
Control measures, such as proper disinfection, filtration and storage of source water, avoidance of dead ends in pipes and regular cleaning and disinfection of spas are therefore required to reduce the risk of legionellosis on ships.