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Mystery sapovirus strikes nursing homes, new tests reveal

Dr. Charles Humphrey, CDC

Sapovirus, previously regarded as rare, is showing up more often as the nasty culprit between outbreaks gastrointestinal illness in nursing homes.

For sheer misery, few germs can cause the chaos of norovirus in a nursing home.  The gut bug can spread rapidly through food, on surfaces or person-to-person, afflicting victims with violent diarrhea, vomiting and stomach pain.

About 20 million people suffer from acute norovirus infections in the U.S. each year, health officials say, but new research suggests that the nasty germ has an equally cruddy but little-known cousin: sapovirus.

Health researchers in Oregon and Minnesota have discovered that once-rare sapovirus may be more common than thought and, worse, on the rise, particularly in nursing homes and long-term care centers.

“It’s an up-and-coming bug,” said Lore Elizabeth Lee, an Oregon public health epidemiologist and author of a new study on sapovirus in the journal Emerging Infectious Diseases.

A review of2,161 gastrointestinal outbreaks in the two states yielded some surprising results. Sure, more than half of the outbreaks were caused by norovirus, and nearly a quarter were caused by bacteria, parasites or other agents, as expected.

But among 142 non-norovirus outbreaks that remained a mystery, scientists tested samples from 93 and found that nearly a quarter were caused by the new culprit,sapovirus, Lee said.

“It means we have another virus circulating that we need to study,” she explained.

The virus operates about the same as norovirus, mostly causing diarrhea, vomiting and, in some cases, fever. It appears to spread in the same ways: person-to-person, on surfaces and through food.

Of the 21 sapovirus outbreaks detected by Lee and her colleagues, 66 percent occurred in long-term care centers, another 10 percent occurred in schools and the rest occurred in familiar norovirus venues: a prison, a large psychiatric hospital, a restaurant and a cruise ship.

That means that sapovirus, once regarded as a sporadic illness in children, may be spreading its gastrointestinal misery in a similar pattern as norovirus, including in nursing homes and beyond. “It’s probably circulating in a lot of other settings as well,” Lee said.

Part of the same family of Caliciviridae viruses, norovirus and sapovirus are separate bugs. Sapovirus was first detected in 1977 at a home for infants in Sapporo, Japan, where it got its name.

It appeared mostly to lie low for a quarter-century, until 2002, when scientists developed a new test for the virus and suddenly found it showing up in more places. “The reason we’re seeing it now is we’re actively testing for it,” Lee said.

All of that is important because of the potential harm of a gut bug like this. Norovirus is the leading cause of foodborne disease outbreaks in the United States, and a similar bug could be responsible for more of those illnesses as well.

In most people, it’s a miserable but brief bout. But in children, the elderly or people with weakened immune systems, it can lead to hospitalization or even death.

Being able to identify the virus behind disabling outbreaks is important, Lee said.

Minnesota is testing for sapovirus and Oregon will soon begin, Lee said, with other states following in the future, perhaps.

In the meantime, the same steps that prevent norovirus will knock down sapovirus as well. That means good hand hygiene, careful food preparation and scrupulous attention to environmental cleanliness.

“Bleach,” said Lee. “Strong bleach.”

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