As the public health emergency stemming from the flu continues statewide, federal health officials are alerting the public to yet another viral illness that's causing queasiness and misery.

Cases of norovirus, the so-called cruise ship infection, are being reported all over the country, according to the Centers for Disease Control and Prevention.

And a new strain that's circling the globe has been reported in small numbers in this state, virus trackers with the New York State Department of Health have found.

The new norovirus strain has been reported in Britain, France, Japan and New Zealand. But experts say the new strain doesn't cause an infection remarkably different from variants in circulation for years.

Dr. David Hirschwerk, an infectious disease specialist with the North Shore-Long Island Jewish Health System, said norovirus is sometimes mistakenly called stomach flu and is exceptionally easy to catch.

"It takes very few viral particles to infect someone; that's why it spreads so easily," Hirschwerk said.

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"Your best defense is hand-washing."

There is no vaccine or medication that can treat it. Doctors recommend allowing the infection to run its course.

Norovirus causes fever, stomach cramping, nausea, vomiting and diarrhea, and usually lasts 48 hours in otherwise healthy people, Hirschwerk said.

He added the infection may last longer in elderly people or those whose immune system is impaired.

In some instances, norovirus is transmitted through food via preparers' unsanitary hands.

Its prevalence on Long Island comes nowhere near that of the current flu outbreak, which compelled the governor during the weekend to declare a public health emergency.

"We haven't seen it as much as we've seen respiratory illness, which is what is predominating here," said Dr. Alan Bulbin, director of infectious diseases at St. Francis Hospital in Flower Hill.

"This infection is often called the cruise ship virus because of outbreaks during cruises with a dense population and close-quarter contact," Bulbin said.

He noted that norovirus causes what doctors refer to as gastroenteritis.

State health department spokesman Peter Constantakes said norovirus is not a reportable infection, so the state does not keep detailed records on its incidence, making it impossible to determine how many cases have occurred.

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Laboratory testing is also difficult, he added, because the infection's course is so short.

Most people self-treat at home, bypassing physicians who otherwise could submit samples for testing.

Still, there have been six reports of the new strain, which have been confirmed in recent weeks, all of which occurred in the metro New York / Long Island area, Constantakes said.

Grace Kelly-McGovern, spokeswoman for the Suffolk County Department of Health, also noted in recent weeks that a few clusters of norovirus infection have been identified, but it's not known whether they were the new strain or one that has circulated before.