Viral Causes of Gastrointestinal Illness

The Norwalk virus is the most common cause of viral gastrointestinal outbreaks on cruise ships, with more than three-fold increase in 2002 over each of the previous three years. Philip Tierno, author of the book The Secret Life of Germs, estimates that 80% of all infectious illnesses, from the common cold to flesh-eating bacteria, are transmitted by direct contact with another person, or indirect contact by touching an inanimate object that a sick person has affected.

Viruses, incuding such as the Norwalk virus, can also be transmitted through food contaminated before it arrives on the ship or in its preparation by infected food handlers. Potable water on the ship may also be a source of viruses.  gastroenteritis viruses are divided into several major categories including rotaviruses, adenoviruses, caliciviruses, astroviruses, Norwalk virus, and a group of Noroviruses.

The close living quarters of ships can provide increased person-to-person transmission of viral agents. Gastroenteritis outbreaks would normally end after all susceptible persons have been infected; however, with cruise ships, new and uninfected populations usually arrive every 1 or 2 weeks, sometimes with less than a few hours between disembarkation of one group of passengers and the embarkation of others, thereby renewing the epidemic with a new set of ‘host organisms.

The Nantucket Clipper provides the two best examples of Norwak virus outbreaks over successive cruises in the last 8 years. One of the smallest ships, the Nantucket Clipper, with less than 100 passengers plus a crew of less than 25, suffered from five successive virus outbreaks in the same number of weeks in January 1999.  One year later, in February 2000, the same ship had three more successive Norwalk virus outbreaks.

In 2006, the CDC decided it's not in the best interest of the cruise lines to report gastrointestinal outbreaks on ships that carry less than 100 people. So, in other words, never cruise on a ship that carries less than 100 people as when an outbreak occurs, it may affect the majority of the passengers and crew and be present on successive cruises without it ever being known by prospective passengers.

Outbreaks of Norwalk-like viruses as well as hepatitis A and the calicivirus, have been associated with consumption of produce. Land-based outbreaks have been associated with frozen raspberries or frozen strawberries, lettuce, melons, salads, watercress, diced tomatoes, and fresh-cut fruit.

A number of these outbreaks were the result of contamination via an infected food handler during final preparation. Hepatitis A and Norwalk-like viruses are the most commonly documented viral food contaminants yet there have been no outbreaks of Hepatitis A on cruise ships documented since 1994.

Viruses can be excreted in large numbers by infected individuals and have been isolated from sewage and untreated wastewater used for crop irrigation. Although viruses cannot grow in or on foods, fresh produce may act as transmission mechanism (medium) for viral pathogens to humans. The survival of viruses on vegetables has been studied. Several enteroviruses (poliomyelitis, enteroviruses, hepatitis A, rotavirus, and Coxsackie viruses) can survive in a variety of raw vegetables for periods exceeding the normal shelf life of salad vegetables. Survival appears to be dependent upon the pH, moisture content, and temperature.

Of 14 reports of viral gastroenteritis outbreaks cited by Hedberg and Osterholm (1993), a food handler who was ill before or while handling the implicated food was identified as the source of infection in eight outbreaks. Salads were the implicated vehicle in five outbreaks (36%), and cold food items or ice were implicated in all but one outbreak. {Center for Food Safety and Applied Nutrition, 2001 122 /id}

References

Philip M.Tierno, 2001,, CDC, 2003,, CDC, 1990, Center for Food Safety and Applied Nutrition, 2001

Viral Gastrointestinal Agents

Norovirus (Norwalk Virus)

Hepatitis A and Norwalk-like viruses are the most commonly documented viral food contaminants and the Norwalk virus is the most common cause of cruise ship gastrointestional outbreaks.  Although viruses cannot grow in or on foods, their presence on fresh produce, which may serve as vehicles for infection, is of concern.  Outbreaks caused by the Norwalk-like viruses have been associated with the consumption of produce including frozen raspberries or frozen strawberries, lettuce, melons, salads, watercress, diced tomatoes, and fresh-cut fruit.  Salads and cold food items or ice have been implicated. (Center for Food Safety and Applied Nutrition, 2001)

A number of these outbreaks were the result of contamination via an infected food handler during final preparation. Hepatitis A and Norwalk-like viruses are the most commonly documented viral food contaminants. Viruses can be excreted in large numbers by infected individuals and have been isolated from sewage and untreated waste-water used for crop irrigation. (Center for Food Safety and Applied Nutrition, 2001)

Rotovirus

Hepatitis A

{Center for Food Safety and Applied Nutrition, 2001 122 /id}

Frozen raspberries or frozen strawberries have been linked to two at least two outbreaks of hepatitis A. Hepatitis A, a virus spread by human feces, is thought to have contaminated the berries by contact with infected harvesters or contaminated irrigation water.  (Center for Food Safety and Applied Nutrition, 2001)