Those Nasty Noroviruses
May Be Getting Nastier

By Helen Branswell
Canadian Press

In a matter of a few years, the term Norwalk virus has become part of the public lexicon. At this time of year, it seems like it's everywhere: grounding planes and closing daycares, spreading misery in long-term-care facilities and schools.
Infectious-disease experts say they think outbreaks are more common and there's something changing in the behaviour of the nasty noroviruses.
"We certainly believe that what we've seen over the last five years is an increase in the activity of this virus," said Dr. Paul Sockett of the Public Health Agency of Canada.
"And this is early stages yet but we have some evidence which suggests that we may have a slightly more virulent strain that's been circulating in the past couple of years," he said, adding the bug has been sowing misery "fairly well across the country."
Dr. Sockett, who works in the agency's centre for infectious-disease prevention and control, acknowledges the increase may be partly attributable to the fact that public-health officials are paying more attention to noroviruses.
But he believes the increase in cases reported to laboratories across the country can't be explained away by more vigilant reporting -- there were 300 to 400 reports a year in 2003 and 2004, up from a mere 14 in 1998.
Dr. Sockett's observations confirm concerns being voiced by infectious-disease specialists, who have been worried by the apparent explosion of outbreaks caused by noroviruses -- the family to which Norwalk and Norwalk-like viruses belong.
Infectious-disease specialist Dr. Michael Gardam was one of those who suspected something about the norovirus situation had changed, noting it has grounded planes and brought cruise ships to dock.
"If you think about what's happened to the cruise industry -- that didn't happen 10 years ago. That really is something that seems to be fairly new," said Dr. Gardam, director of infection prevention and control at Toronto's University Hospital Network. "There's no doubt Norwalk seems to be a bigger player than it was six years ago."
But Dr. Gardam admitted that's a gut feeling -- a gut feeling that in the recent past would have been impossible to prove.
He and others acknowledge the sense of increased activity could be, at least in part, due to greater attention being paid to noroviruses because of the havoc they wreak in hospital settings and because it is now easier to study the viruses.
Until recently, there was little incentive for doctors or hospitals to send stool samples for testing for norovirus. They could diagnose from clinical symptoms and knew that while the disease was miserable, it was rarely life-threatening.
And there was little point to sending samples to the lab; the virus can't be grown in culture, so there was no way to produce a viral isolate to study.
With the development of polymerase chain-reaction testing, laboratories can now amplify pieces of the virus and produce a genetic fingerprint that can be compared to the fingerprint of other noroviruses.
That opens up research possibilities that need to be explored, said Dr. Allison McGeer, head of infection control at Mount Sinai Hospital in Toronto.
"The argument for not studying them is people don't die from them very often... but from an institutional-disruption point of view, they're expensive as all get out," she said.
"And I think that means we've got to sit down and figure out what we're doing with them."
The Public Health Agency is trying to do just that. Last week it convened a meeting of provincial and territorial public-health officials to try to get a handle on the problem.
"Certainly one of the things we would like to do is to sort of collect the different strains and catalogue them and see where they're appearing in the country to see if there's any connect between them and what types of evolution in those strains are taking place," Dr. Sockett said.
The laboratories of the British Columbia Centre for Disease Control have been doing that type of tracking for the past four years, producing Canada's first database of about 350 viral fingerprints dating back to 1994 from frozen stool samples.
They've seen a dominant strain, said Dr. Judy Isaac-Renton, director of laboratory services. It was the seventh strain they typed in 2002; they called it 007.
"We always have a picture of James Bond on it because it has the licence to ill," Dr. Isaac-Renton said with a chuckle.
Having viral fingerprints allows public-health authorities to track the progress of particular viruses, but the science hasn't yet evolved to the point where they can tell if one causes worse disease than another, she noted.
But Dr. Isaac-Renton does believe the pattern of disease has changed, with a worrisome increase of norovirus outbreaks in health-care institutions.
"It's changing in the sense that it's now impacting very severely ill people in acute-care hospitals. And to me that's a significant change."
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