Japan tourists point to the sights around dock where the cruise ship The Queen Elizabeth 2 is docked following a norovirus outbreak. (Marco Garcia/Associated Press)

A new strain of stomach bug sweeping the globe is taking over in the U.S., health officials say.

Since September, more than 140 outbreaks in the U.S. have been caused by the new Sydney strain of norovirus. It may not be unusually dangerous; some scientists don't think it is. But it is different, and many people might not be able to fight off its gut-wrenching effects.

Clearly, it's having an impact. The new strain is making people sick in Canada, Japan, Western Europe, and other parts of the world. It was first identified last year in Australia and called the Sydney strain.

In the U.S., it is now accounting for about 60 per cent of norovirus outbreaks, according to report released Thursday by the Centers for Disease Control and Prevention.

Norovirus — once known as Norwalk virus — is highly contagious and often spreads in places like schools, cruise ships and nursing homes, especially during the winter.

Last month, 220 people on the Queen Mary II were stricken during a Caribbean cruise.

Sometimes mistakenly called stomach flu, the virus causes bouts of vomiting and diarrhea for a few days.

Every two or three years, a new strain evolves — the last was in 2009. The Sydney strain's appearance has coincided with a spike in influenza, perhaps contributing to the perception that this is a particularly bad flu season in the U.S.

Ian Goodfellow, a prominent researcher at England's University of Cambridge, calls norovirus 'the Ferrari of viruses' for the speed at which it passes through a large group of people.

"It can sweep through an environment very, very quickly. You can be feeling quite fine one minute and within several hours suffer continuous vomiting and diarrhea," he said.

Health officials have grown better at detecting new strains and figuring out which one is the culprit. They now know that norovirus is also the most common cause of food poisoning in the U.S.

It's spread by infected food handlers who don't do a good job washing their hands after using the bathroom. But unlike salmonella and other foodborne illnesses, norovirus can also spread in the air, through droplets that fly when a sick person vomits.

"It's a headache" to try to control, said Dr. John Crane, a University of Buffalo infectious disease specialist who had to deal with a norovirus outbreak in a hospital ward a couple of years ago.

Each year, noroviruses cause an estimated 21 million illnesses and 800 deaths, the CDC says.

For those infected, there's really no medicine. They just have to ride it out for the day or two of severe symptoms, and guard against dehydration, experts said.

The illness even got the attention of comedian Stephen Colbert, who this week tweeted: "Remember, if you're in public and have the winter vomiting bug, be polite and vomit into your elbow."