SYDNEY – A virus that caused a spate of vomiting and diarrhea in Asia last winter appears to be spreading globally, threatening larger outbreaks of gastro infections that are a bane of luxury cruises.
The new strain of norovirus known as GII.17 that emerged in southern China has the potential to spread widely because people will probably lack immunity to it, researchers in Japan said Thursday. That means the bug, which kills about 800 people in an average year in the U.S., could sicken hundreds of millions of people worldwide as the highly contagious disease is transmitted by infected food and people.
“We know that noroviruses are able to rapidly spread around the globe,” scientists from 16 countries wrote in a paper accompanying the Japanese research. “The public health community and surveillance systems need to be prepared in case of a potential increase of norovirus activity in the next seasons” caused by this novel strain.
Norovirus made headlines last month when an outbreak of gastroenteritis on Fred.Olsen Cruise Lines’ flagship vessel, the Balmoral, sickened “hundreds” of people in Scandinavia, prompting the cancellation of a subsequent three-night cruise from England. A gastro outbreak occurred on the same ship the previous month, the Daily Mail newspaper reported. Norovirus was the culprit, the Ipswich, U.K.-based company said in a June 12 statement on its website.
Norovirus infections, sometimes called “stomach flu” or “winter vomiting disease,” usually occur in winter. An increase in the frequency of outbreaks on cruise ships over summer can predict a greater incidence in the community next winter, said Marion Koopmans, a professor of public health virology at Erasmus University Medical Center in Rotterdam, Netherlands, in an interview Friday.
Outbreaks on cruise ships are especially noticeable because the contained environment and shared dining areas allows the disease to spread quickly — more than 80 percent of passengers can be affected, according to the World Health Organization. But the vast majority of epidemics actually occur on land.
Like flu, new strains emerge as the virus mutates, but while flu typically mutates quickly, new norovirus bugs tend to emerge only every two to four years, often leading to gastroenteritis pandemics that send hundreds of thousands of people to hospital.
“What this could mean is that we’re looking at the emergence of a new genotype,” said Koopmans, who was a co- author of one of the two papers published last week. The new GII.17 virus could replace GII.4 to become the dominant strain circulating in other parts of the world, she said.
There is no specific medicine to treat the infection. Takeda Pharmaceutical Co., based in Osaka, Japan, has the most advanced vaccine in development. Scientists will need to study whether it will work against the new strain, Koopmans said.
Cases of GII.17 have been detected in the U.S., South America, Europe and Africa, Koopmans and colleagues wrote.
Infected food workers are frequently the source of norovirus outbreaks, often by touching ready-to-eat foods served in restaurants, according to the CDC. As few as 18 viral particles on food or hands can make someone sick, which means the amount of norovirus on the head of a pin would be enough to infect more than 1,000 people.
That’s made it the bane of luxury cruise lines. The CDC has reported nine outbreaks on cruises already this year among vessels it monitors, compared with eight in 2014 and eight in 2013.
Preventing the introduction of gastrointestinal illness is one of the cruise industries’ top priorities, the Cruise Lines International Association says on its website. Members take steps to prevent sick passengers from bringing norovirus on board and if an outbreak does occur, work to mitigate its spread and treat those who are ill, the Washington-based group says.
“The cruise ships have gone to long lengths to make sure that gastroenteritis outbreaks are contained,” said Martyn Kirk, an associate professor in the college of medicine, biology and environment at the Australian National University in Canberra. “They’ve got quite slick at making sure people stay in their rooms, that ships are disinfected between cruises.”
Norovirus causes 19 million to 21 million cases of acute gastroenteritis a year in the U.S., leads to 400,000 emergency department visits, and about 56,000 to 71,000 hospitalizations and as many as 800 deaths, mostly among young children and the elderly, the CDC says.
“For many people, it is a nuisance,” Koopmans said. “You have two days of vomiting, diarrhea, and then that’s it. The majority of cases have a fairly mild disease course.”
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