Cruise Ships and Norovirus Outbreaks
Norovirus infection is characterized by abdominal cramps, vomiting, and diarrhea that lasts 1-3 days. It may also increase the risk of developing irritable bowel syndrome, and cause chronic diarrhea in immunocompromised or elderly individuals. It is spread by three different means:
Public vomiting, which exposes anyone in a 10 meter radius.
Fecal-oral surface transmission (poor handwashing after bowel movement), contaminating railings, elevator buttons, public restroom fixtures, self service utensils. The virus continues to be shed in the feces for several weeks after infection.
Food/water/ice contamination. Poor hygiene can cause human contamination of food, ice machines, or water dispensers.
The incubation period is 12-48 hours after exposure.
80% of norovirus infections occur in the winter months, and are widespread - 700 million cases annually. They occur worldwide, including developed nations with good sanitation and hygiene conditions. Up to 30% of people are carriers who may pass it on to others. After infection, an individual is immune to that strain of virus, however that immunity only lasts 8 weeks to 6 months. The virus mutates quickly, making the development of a vaccine unlikely. In any environment where people live in close quarters, a large norovirus outbreak is possible.
Cruise ships have been associated with norovirus despite rigorous sanitation, intensive crew training, and preventive measures taken by the cruise line industry. The Centers for Disease Control (CDC) has a Vessel Sanitation Program (VSP) in which many cruise lines choose to participate. Norovirus outbreaks do occur on cruises, however the incidence is low. A study of acute gasterenteritis on cruise ships from 2008-2014 suggests the risk of an outbreak on a cruise was 0.5%, and the risk of a passenger contracting acute gastroenteritis was 0.18%. Of these, only a fraction were determined to be norovirus.
Due to the contagious nature of this infection, cruise lines offer complimentary medical care and incentives to passengers (free room service, free movies, a visit from a mascot, credit towards future cruises) to adhere to a short quarantine in their room. However, passengers often do not report illness, break quarantine, even deny illness if asked by crew or on a pre-boarding questionnaire.
Alcohol sanitizers have questionable efficacy against norovirus, even at high concentrations. Proper and frequent handwashing, avoiding contact with surfaces that could be contaminated, avoiding ice machines, and avoiding public restrooms are effective precautions.
Norovirus often presents with other infections. Taking medication or vaccines to prevent other illnesses is also a sensible preparation.