Norovirus: Not just for cruise ships

My aunts and uncles love going on cruise ships. Puerto Vallarta, Caribbean, Baltic Sea, Alaskan coast, the Mediterranean, etc. They've been there, done that. I have never been interested in going on these cruises. Why not?

Norovirus.

Every month there seems to be another headline bemoaning the latest outbreak of food poisoning on some cruise liner. Nearly without exception, the culprit is norovirus. In certain cases, the number of afflicted has been quite high; earlier this year 600 passengers and crew members of the cruise ship Explorer of the Seas were sickened by norovirus (Figure 1).

What is Norovirus? From Wikipedia:

"The [noro]viruses are transmitted by fecally contaminated food or water, by person-to-person contact, and via aerosolization of the virus and subsequent contamination of surfaces. Noroviruses are the most common cause of viral gastroenteritis in humans, and affect people of all ages.

Norovirus infection is characterized by nausea, forceful vomiting, watery diarrhea, abdominal pain, and in some cases, loss of taste. General lethargy, weakness, muscle aches, headache, and low-grade fever may occur. The disease is usually self-limiting, and severe illness is rare. Although having norovirus can be unpleasant, it is not usually dangerous and most who contract it make a full recovery within a couple of days."

So when you have "stomach flu" (i.e. viral gastroenteritis) it is likely to be caused by norovirus and not flu virus. As stated above, it is not a life-threatening ailment for most people i.e. "while rarely fatal, the CDC says norovirus can lead to severe dehydration and hospitalization for children, elderly adults and those with preexisting health conditions, and causes an estimated 570 to 800 deaths in the United States each year."

Norovirus is the number one cause of food poisoning in America; 20 million Americans suffer from it each year (between 5 and 10% of the population). And no these 20 million Americans did not all get norovirus from a cruise; indeed, only 1 percent of norovirus outbreaks occur on cruise ships.

One characteristic of norovirus that makes it prevalent is that it can spread rapidly:

“Food workers continue to be the primary source of contamination and have the potential to significantly amplify community transmission of noroviruses through widespread exposure,” the CDC reported concluded. Most of the food-borne spread of the pathogen occurs in restaurants and via catering, where food workers touch food such as salad vegetables, fruit and food that already has been cooked, immediately before it is consumed, the report said.

It is important to note that there are many other causes of food poisoning; these include other viruses (Hepatitis A), bacterial contamination (e.g. E. coli in meat, Salmonella), parasites (Trichinella), toxins, etc. Indeed every year 76 million people become ill from the food they eat; as mentioned above, norovirus accounts for about 20 million of these cases.

So why are cruise ships always in the news? The extended confined setting of a ship with many passengers make it susceptible to a norovirus outbreak. Norovirus is very contagious (i.e spreads rapidly), hard to kill, and can persist on food or the surfaces of kitchens for long periods of time.

The CDC notes that there is neither a vaccine to prevent norovirus infection nor a drug to treat it; most people recover in one to three days on their own. Washing your hands is the best form of prevention, while staying hydrated is the best treatment.

To avoid norovirus the CDC "recommends washing raw foods, such as salad vegetables, right before you eat them, even if they are packaged and advertised as pre-washed."

There have been 33 outbreaks of norovirus on cruise ships over the last 3 years or about 10 per year, whereas there are roughly 10,000 cruises per year, and so the norovirus outbreak percentage is less than 1% (closer to 0.1%).  So go ahead and take that Caribbean cruise; the chances are small you will get norovirus food poisoning. For me there is a second reason why I don't go on these cruises: I am afraid of water.

Figure 1. A norovirus incubator?