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Editor: Rod Sullivan
Profession: Maritime Attorney

Category: Safety at Sea

On November 19, 2006 the Carnival cruise ship Carnival Liberty docked in Port Everglades after a 16 day transatlantic crossing from Europe during which over 600 people became ill from Norovirus. Passengers began showing symptoms as soon as the ship got underway. Most were better by the time the ship reached Port Everglades.

Norovirus is highly contagious and causes acute gastroenteritis (AGE) (inflamation of the stomach and intestines). The symptoms include nausea, vomiting, and diarrhea. As few as 10 viral particles may be sufficient to infect an individual.

Most foodborne outbreaks of norovirus illness come from direct contamination of food by a food handler immediately before its consumption. Outbreaks are frequently associated with consumption of cold foods, including various salads, sandwiches, and bakery products. Liquid items (e.g., salad dressing or cake icing) that allow virus to mix evenly are often implicated as a cause of outbreaks. Other foods, including raspberries and salads, can be contaminated before serving and cause extensive outbreaks.

Norovirus is one of the "Norwalk-like viruses", or human noroviruses (HNVs). It has an incubation period of 24-48 hours. Most patients recover from the acute infection within 24 to 48 hours (mean is 33 hours) and experience no chronic (long-lasting) symptoms. The most severe cases last for about 6 days. Noroviruses are not affected by treatment with antibiotics, and cannot grow outside of a person's body. They can live outside a person's body though.

During a typical outbreak, 15% of the passengers and crew will report to the infirmary for treatment while another 10% will suffer the effects of the virus, but will remain in their cabins.

Noroviruses are found in the stool or vomit of infected people. People can become infected with the virus in several ways, including by eating food or drinking liquids that are contaminated with norovirus, touching surfaces contaminated with norovirus, and then placing their hand in their mouth, or having direct contact with another person who is infected and showing symptoms. Once the virus breaks out, it can be found on handrails, elevator buttons, and anywhere infected passengers may place their hands. Frequent handwashing reduces the spread of the infection. On most ships, the ship's Captain will no longer shake hands with passengers to avoid potentially spreading the virus.

People begin being contagious as soon as they begin having symptoms, and remain contagious for three days after the symptoms disappear. Some people may be contagious for as long as 2 weeks after recovery.

The typical mode of contagion begins with foodborne transmission in the shipboard restaurants, followed by secondary person-to-person transmission. Although presymptomatic viral transmission (called "shedding") may occur, shedding usually begins with onset of symptoms and may continue for 2 weeks after recovery.

After an incident like this, extensive decontamination of the ship is necessary. The Center for Disease Control (CDC) recommendations include washing surfaces with suitable disinfectants like freshly prepared chlorine solutions at concentrations of >1,000 ppm, phenol-based compounds, and hydrogen peroxide products. Cruise ships also should promote frequent, rigorous hand washing with soap and water by passengers and crewmembers.

Noroviruses are able to survive freezing, temperatures as high as 140°F. Noroviruses can survive in up to 10 ppm chlorine, well in excess of levels routinely present in public water systems.

Relatively simple measures, such as correct handling of cold foods, strict hand washing after using the bathroom and before handling food items may substantially reduce foodborne transmission of noroviruses.

Prevention of norovirus disease spread via droplets from vomitus (person to person transmission) should focus on methods to limit transmission including isolation precautions (e.g., cohort sick patients in a healthcare facility) and environmental disinfection.