Sick from my cruise: Norovirus is all around us

If you're a breathing human being, chances are you've eaten it.

The intestinal ailment dubbed the Norwalk virus is so common that 23 million Americans ó one in 10 ó suffer from its symptoms each year.

The cruise-ship industry has been hit hard recently by the illness, which has afflicted thousands of passengers in the past six months. Seattle-based Holland America canceled two cruises ó one on the Ryndam and another on the Amsterdam ó so crews armed with steam cleaners and chlorine solutions could scour every inch of the luxury liners after passengers got sick on back-to-back cruises. Disney Cruise Line canceled a cruise aboard the Magic. Other cruise lines have experienced large-scale outbreaks.

But experts say people are susceptible to the virus simply by stepping outside of their homes. "These are extremely common outbreaks," said Marc-Alain Widdowson, an epidemiologist with the Centers for Disease Control and Prevention's Respiratory and Enteric Viruses branch. "It's probably the leading cause of diarrhea in the U.S., so when people are assessing their risks of going on a cruise, ... they should know that going to that restaurant down the road is just as risky."

'A lot to learn'

First identified in 1972 by National Institutes of Health scientist Albert Kapikian, the virus was named after an outbreak at an elementary school in Norwalk, Ohio, four years earlier. Scientists mapped the virus' genetic makeup in 1990, but they haven't been able to grow the virus in a laboratory, leaving many unanswered questions.

"This is all relatively new information," said Kim Green, a scientist with the National Institute of Allergy and Infectious Diseases. "We still have a lot to learn."

Scientists know there are potentially 50 strains of Norwalk-like viruses ó classified as Noroviruses ó that produce symptoms such as vomiting, diarrhea, fever, abdominal pain and nausea for one to three days. And they know it is transmitted through contaminated food or water as well as person-to-person contact.

They don't know why some people get it but don't show symptoms. They don't know which disinfectants kill it. And they don't know why there seem to be more outbreaks during the winter, though scientists speculate it may be because people are indoors more.

Although the first known outbreak was in 1968, scientists suspect the group of viruses has been infecting people for decades or longer. People often use the terms "24-hour flu" and "stomach flu" to describe what are actually Norwalk-virus infections, said Green. Sometimes it's also the culprit in "food poisoning," which has come to be a catch-all phrase for viruses, bacteria, mushrooms or even toxins transmitted by food.

Highly contagious, the virus infects 50 to 70 percent of those who are exposed to it. "Outbreaks are most likely to occur in settings where there are a lot of people close together. That's why it often happens at schools and camps," said Green. "It also occurs frequently in nursing homes."

In the latest development, the infection has been sweeping through hospitals in Ontario, Canada, causing a number of them to close wards.

Even though the number of sick aboard cruise ships has climbed into the thousands recently, it's still a smaller percentage of cruise passengers than in past years ó given the rise in the number of those taking cruises, said Dave Forney, chief of the CDC's Vessel Sanitation Program.

Dirty oysters

Transmission of the Norwalk virus is officially classified as fecal-oral ó generally meaning that people use the bathroom and don't wash their hands properly, then touch something that others subsequently put in their mouths.

The most common sources are oysters and other shellfish harvested from water contaminated by sewage, or infected people spreading it through salads and other foods they handle.

People can also spread it by tainting surfaces such as handrails and counters, and there's even a case of a football team transmitting the illness to a rival team during a game.

Scientists are still learning about other types of transmission. They believe the virus may be able to aerosolize and infect people who breathe it in.

"There are stories of people traveling on a bus when someone vomits," said Mary Estes, director of the Texas Gulf Coast Digestive Disease Center at Baylor College of Medicine in Houston. "Although the people on the bus didn't have direct contact with the vomit, 50 percent of them came down sick."

Scientists don't know exactly how long the virus can live on a surface, but they suspect it survives for several weeks. And an infected person is contagious for up to two weeks after recovering from symptoms.

Intense heat and high concentrations of chlorine can kill the virus, but scientists don't know what other disinfectants are effective. And because it's difficult to test an environment to see if the virus is present, they've only been able to take a wait-and-see-if-people-get-sick approach with cruise ships and other outbreak sites.

Shaking hands on the ship

Complicating the process of tracing the spread of the ailment is a group of people who are infected and spreading the virus, but never show any symptoms ó about 30 percent of those infected.

"They're still shedding the virus walking around the ship shaking hands and doing things with other people," said Estes, who headed the lab that mapped the virus' genetic makeup. "They're not sick, so they don't think they're infected."

This makes researchers think some people may be genetically susceptible to the illness.

Every person who has been studied in Norwalk-virus research has had some virus antibodies, which are formed when the body heads off an infection, leading scientists to believe that every adult has been exposed to the virus. But because the protection wears off after a while, most people will be infected every one or two years, said Estes.

"It's kind of like the common cold of the intestinal tract," she said.

While the virus was traditionally believed to affect mainly older children and adults, scientists believe younger children and infants may be susceptible as well.

Although the virus is not considered life-threatening, people with compromised immune systems, such as the elderly, are more vulnerable to complications that may require hospitalization.

A vaccine in the works

Estes is in the early stages of testing a vaccine created with insect cells. And Charles Arntzen, founding director of the Arizona Biodesign Institute at Arizona State University, is awaiting Food and Drug Administration approval for human testing of a vaccine made from genetically-altered tomatoes.

"Anyone who wants to avoid an unpleasant bout of 'food poisoning' may have to take it once a year," said Arntzen, although a readily available vaccine is still years away. "It'll be like a flu shot."

Seattle Times staff reporter

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