Swine flu spread in North America may extend into summer, experts say

TORONTO - Spread of swine flu in North America may not dampen down in coming weeks as was first expected, some health officials and flu experts are now suggesting.

TORONTO - Spread of swine flu in North America may not dampen down in coming weeks as was first expected, some health officials and flu experts are now suggesting.

Some are now planning for the possibility the new virus may continue to trigger infections into the summer, not petering out in the way seasonal flu strains typically do as temperatures rise in the Northern Hemisphere.

"This is what worries me," says Dr. Arnold Monto, an influenza expert at the University of Michigan's School of Public Health.

"We are seeing a fair amount of circulation of the swine flu virus. And I'm not yet convinced that it's going to go away completely."

"It may dampen down a bit as schools close. But I think we're still seeing increasing transmission in the U.S. And I think in addition you have far more transmission in Canada than some people are saying - it's not just imported cases and circles around imported cases."

Monto's concern is echoed by Dr. Allison McGeer, an influenza expert at Toronto's Mount Sinai Hospital.

McGeer says abnormal flu activity levels for this time of year are making her question "the delusion that this was actually going to quiet down and we weren't going to have a first wave" over the late spring and summer.

"On a relative scale there's not a lot of it," she says of swine flu transmission in Canada's largest city.

"But it's very clearly starting to increase. I suppose it could shut itself off at any given time. But the last couple of days look like we're going to see a (flu) season," McGeer said.

"In Toronto, at least, I think we're gone."

If the virus were to take a summer hiatus in the Northern Hemisphere, it would give public health officials more time to plan for a possible surge in cases in the fall. The swine flu virus is now causing mild illness in the vast majority of cases, but experts fear that could change as the new virus evolves.

It would also buy time on the vaccine front. Vaccine production has not yet begun and it is expected it would take between four and six months before the first doses would be ready.

The U.S. Centers for Disease Control is now working the possibility of a summer wave into its planning, a senior official with the agency admits.

"CDC is preparing for the possibility that influenza may continue to circulate at present levels through the summer," says Dr. Daniel Jernigan, deputy director of the influenza division.

"For seasonal influenza, activity (during summer) generally drops to a very low level, however, with this new H1N1 strain, we may see some continued activity."

"One strong possibility is that the new strain will begin increasing in activity early this fall, and we want to be prepared for that."

Sunday marked one month since the CDC sounded an international alarm about a new swine flu virus potentially spreading among humans.

The agency had received a virus sample retrieved from a boy in San Diego, Calif., who had been sick with influenza like illness. Testing suggested he was infected with an influenza A virus. But standard diagnostics that look for known human flu strains could not subtype the virus.

The CDC labs confirmed the boy - who had had no contact with pigs - had been infected with a never-before-seen swine flu virus. On April 17, American authorities notified the World Health Organization that a virus with pandemic potential might be circulating in the U.S. Southwest.

In short order the WHO raised the global pandemic alert level to Phase 5, the brink of a pandemic.

By Sunday, laboratories in 39 countries around the globe had confirmed nearly 8,500 cases, a figure that is without doubt only a fraction of the actual infections that have occurred. Late last week the CDC's Jernigan estimated upwards of 100,000 people in the U.S. may have been infected already.

To date four countries have reported a total of 75 deaths due to swine flu infection.

Initially the WHO and authorities in North America predicted rising temperatures and the approaching end of the school year might mean transmission in the Northern Hemisphere would slow to a trickle, with action shifting to the Southern Hemisphere, where the start of flu season is imminent.

For reasons that science can't yet fully explain, human flu viruses don't transmit well during the summers of the Northern or Southern Hemisphere - hence the term "seasonal" influenza viruses.

But it's known from previous pandemics that pandemic viruses can rewrite the rules when they first emerge.

The virus responsible for the Spanish flu pandemic, first spotted in some places in the spring of 1918, returned with a vengeance in late August and early September of that year on the east coast of North America.

That was abnormally early for influenza. Though flu activity can start to pick up in late November, transmission typically takes off around Christmas and peaks sometime in January or February.

- Follow Canadian Press Medical Writer Helen Branswell's flu updates on Twitter at CP-Branswell

 
 
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