Taking Even 2 Safety Measures Can Halve West Nile Infection Risk: Study

TORONTO (CP) – Ever wonder whether dousing yourself with mosquito repellent, donning a shroud of clothing or staying indoors after dusk really will prevent West Nile infection? Well, now there’s proof such measures actually do work.

In fact, a study to be published next month suggests that using even two of the recommended mosquito-busting safeguards can chop the risk of contracting West Nile virus in half.

“There’s always been the public health messaging about West Nile and about using protective behaviour, but no one’s ever quantified it,” said lead author Dr. Mark Loeb, an infectious disease specialist at McMaster University.

“The messaging is correct . . . this is not just common sense, but it’s evidence-based,” Loeb said Thursday from Hamilton. “You will actually substantially reduce your risk of becoming infected with West Nile if you use these personal protective behaviours.”

So far this year, there have been a handful of probable cases of West Nile infection reported in Quebec, Ontario, Saskatchewan and Manitoba (the latter announced its first three probable cases for 2005 on Thursday).

But in 2002, the second year the mosquito-borne disease bit into Canada, there were 86 probable and 340 confirmed cases of West Nile; 20 people died.

One of the hot spots of the infection that year was Oakville, Ont., just west of Toronto, where 60 cases were reported among 400,000 residents.

To determine how prevalent West Nile had become among the local population, Loeb and his team took blood samples in early 2003 from 1,500 residents over age 18 and analyzed them for signs of previous infection. Participants also were surveyed by phone about measures they took to avoid exposure to the blood-sucking insects.

Those measures include:

-Using repellent containing DEET or other approved ingredients.

-Avoiding mosquito-infested areas.

-Wearing light-coloured long pants, long-sleeved shirts and a hat.

-Ensuring door and window screens fit tightly and have no holes.

-Eliminating standing water where mosquitoes breed, such as pool covers and garbage cans.

-Changing water in wading pools, bird baths and pet bowls twice a week.

-Cleaning out eavestroughs regularly to prevent clogs that can trap water.

“And the bottom line is we found that people who use two or more protective behaviours . . . were 50 per cent less likely to become infected with the virus,” said Loeb.

Dr. Ross Findlater, Saskatchewan’s chief medical officer of health, called the Ontario study important because “it provides more evidence that the messages that we’re giving the public are telling them the truth, that the protective measures that we’re advising against mosquitoes actually do work in practice.”

Public health officials in Saskatchewan are holding their breath in anticipation of what this year will bring, especially after experiencing six deaths in 2003. (Last year’s cool weather squashed West Nile before it got going.)

“We’re just nervous about it, I guess,” said Findlater. “The conditions are right, the mosquitoes are out there . . . and we won’t really know for a couple of weeks how much (viral) transmission there’s been.”

He’s hopeful, however, that Canadians have learned how to protect themselves through provincial education campaigns.

But despite ongoing public health reminders, Loeb suspects many Canadians aren’t as vigilant as they once were in safeguarding themselves against infection. Dropping case numbers in the last couple of years may have led to complacency – even though West Nile remains very much a threat, he said.

While the odds are good that the virus will produce only flu-like symptoms in most of those infected, the risk of developing severe disease rises with age. On average, only about one in 85 Canadians gets seriously ill when infected by West Nile. But among those older than 65, the chance of developing potentially deadly or debilitating encephalitis or meningitis ramps up to about one in 30.

“We’re doing another study where there are people in their 50s who are paralyzed due to West Nile,” he said.

The study appears in the September issue of the U.S. Centres for Disease Control journal Emerging Infectious Diseases.