What's up Doc? All flu is not created equal

Dr. Jeff Hersh

Q: Last year everyone at the nursing home where I work got sick with the stomach flu. I also got it, and then my whole family became sick. Will my flu shot prevent that this year?

A: The influenza virus causes the flu, with symptoms such as fever, runny nose, cough, body aches, headache, sore throat and congestion, but not the stomach flu; so the influenza shot (flu shot) does not protect against the stomach flu.

What we mean by the stomach flu (also called viral gastroenteritis or winter vomiting disease) is an illness characterized by nausea, vomiting, stomach cramps, diarrhea, fever and even flu-like symptoms such as body aches and malaise, although not everyone gets all the symptoms.

There are more than 300 million cases of diarrheal illness in the United States each year. These lead to more than 500,000 hospitalizations and 3,000 deaths, mostly in the very old, very young or in people with other debilitating diseases. In kids under 2 years old, the most common cause is rotovirus. In older kids and adults there are many causes.

Outbreaks of the stomach flu happen when the virus causing the disease infects many people in an area at the same time. It is more common in the winter months.

Norovirus, also called Norwalk-like virus, was named after the virus identified as the cause of a large outbreak of stomach flu that occurred in Norwalk, Ohio, in 1968. Although norovirus is responsible for only 30 million or so (10 percent) of the cases of diarrheal illness each year, it is responsible for about 90 percent of "stomach flu" outbreaks. Therefore, norovirus is an appropriate focus.

Norovirus is suspected when there is an outbreak of the stomach flu and the so-called Kaplan criteria (vomiting in over half the affected people; average incubation of the illness of one to two days; average duration of illness of 12 to 60 hours; and no bacteria isolated in stool specimens) are met.

There are many characteristics of the norovirus that make it particularly able to cause outbreaks. People sick from norovirus are contagious as early as 12 hours after they are infected and for a week or more after they have recovered. Very small amounts of virus (as little as 10 viral particles) are enough to make someone sick. There are many strains of norovirus and they are very hardy - resistant to many disinfectants and even heat - so it is hard to clean contaminated materials and surfaces. People who have had the virus do not get long-term immunity, so they can become re-infected.

Norovirus is transmitted by the fecal-oral route; this means someone who is sick goes to the bathroom and does not wash their hands well, so some of the virus shed in their stool (or their vomit) is passed on to the next person, to food or to surfaces in a room. The virus can survive on food and even on metal surfaces for days, so outbreaks can be caused by "food poisoning" or from contaminated surfaces (you touch the contaminated surface and then ingest some of the virus from your own contaminated hands).

Most outbreaks of norovirus-induced stomach flu (40 percent) are from contaminated food, either from the food itself (any food can do it, but shellfish, especially bottom-feeders like oysters, are the most common) or from food contamination from infected food handlers. Another 25 percent of outbreaks occur in hospitals or nursing homes; 10 percent to 15 percent in day care centers; and 10 percent are travel associated (such as the cruise ship outbreaks we have all read about).

Stomach flu symptoms typically last one to two days, so the treatment is to prevent dehydration from the diarrheal fluid loss and the decreased fluid intake from the nausea until the symptoms resolve. Aggressive fluids by mouth are sufficient in an overwhelming majority of patients, although some people will require IV fluids.

Since there are no vaccinations or antiviral medications for norovirus, the key is prevention. This is done by frequent hand washing and careful food preparation. If clothing or bedding is soiled by a sick patient, care must be taken in handling the contaminated materials, which should be thoroughly cleaned. People who work in the food preparation industry who get sick should not work until at least three days after they are fully recovered, and be meticulous with hand washing and wearing gloves when they do return to work.

Jeff Hersh, Ph.D., M.D., F.A.A.P., F.A.C.P., F.A.A.E.P., can be reached at