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Think H7N9 cases are slowing? Too soon to declare virus under control: experts

05/07/2013 06:32 EDT | Updated 07/07/2013 05:12 EDT
The numbers of new cases of H7N9 bird flu are still rising, but these days the daily increase is more a trickle than the gush of a few weeks ago.

That apparent slowing of what had been an explosive growth of infections with the new flu may lead people to hope this virus is being brought under control. Some minds may see a week or two of fewer new cases as a crisis averted.

But experts warn it's far too soon to gauge what H7N9 has in store for humankind. And while the virus initially seemed as if it might be another 2009 H1N1 — new virus, lightning-fast global spread — at this point H7N9 does not appear to be in a sprint to the pandemic declaration line.

It's a bad virus, one that makes people severely ill. And it perplexes authorities trying to find it because it doesn't sicken chickens. That latter fact means China is having a hard time getting a handle on where and how widely dispersed the virus is. Without that knowledge, eradicating it or even bringing it under control is not a likely scenario.

As of Tuesday, the World Health Organization had been informed of 130 infections and 31 deaths. Tuesday's numbers grew by only two cases, a nice change from a couple of weeks ago when the count was rising by five, eight or 10 new cases a day.

Some experts think we may actually be observing a slowing of cases, perhaps due to control measures China has taken. Live animal markets have been closed in three large cities and new infections have dropped off in those locales. Another possible explanation: spring has brought rising temperatures, which aren't generally ideal for the spread of flu viruses.

But Michael Osterholm, director of the Center for Infectious Diseases Research and Policy, cautions that it's premature to declare a pattern of decline at this point.

"Anybody who does influenza surveillance has to understand that one or two weeks does not make for a trend in any way, shape or form," Osterholm says.

He suggests that while flu activity often wanes in warm weather, it doesn't always. The swine flu viruses that were transmitting at U.S. state fairs over the past two summers spread well during warm months and more poorly as temperatures cooled. During the H1N1 pandemic, activity in North America was heavy in August of 2009.

"I think the point I'm just trying to make is that we don't really understand enough to be able to say: 'Warmer weather? Colder weather? More humidity? Less humidity? Sunlight? Less sunlight?' We just don't know," Osterholm says.

Others are expecting a decline in new infections over the summer months.

"I think the numbers may go down — that's probably the best scenario that one can expect — with the summer, but I doubt very much it (the virus) will go extinct," says Malik Peiris, chief of microbiology at the University of Hong Kong.

"So it will smoulder on and it will resurface again in the winter. Now that is probably better than the thing continuing in full force because at least it will give people some time to prepare. But I really would doubt that it will completely disappear."

While a decrease in cases would be welcome, those concerned about this outbreak realize in some ways it could be a mixed blessing. When cases decline, flu gets pushed off the radar. Rather than using the time to prepare for what might be ahead, people may decide this is another instance where warnings of a possible pandemic failed to materialize and dismiss the threat entirely.

"It does become challenging because if we have to continue to track the virus and try to understand if it might be changing over a long period of time, some people lose interest," says Nancy Cox, who heads the influenza division at the U.S. Centers for Disease Control in Atlanta.

"We won't lose interest, but some people lose interest."

Peiris agrees.

"When the human caseload goes down, the whole incentive to do such interventions" — for instance clear up live markets — "on the poultry side will disappear," he warns. "So that will probably not help in that sense."

The World Health Organization's top flu expert thinks the world may be in for a long haul with H7N9.

"Is it possible that this could continue some kind of pattern like this for a while? I think the answer is yes, it's definitely possible," Dr. Keiji Fukuda says.

Still, Fukuda gets that people may be suffering from pandemic or flu fatigue. He also knows that the fact that the other bird flu, H5N1, still has not caused a pandemic after years of warnings about the dangerous virus may erode people's willingness to believe this H7N9 is a threat worth watching.

"If basically some people are saying, 'Well, we've seen this all before and we don't want to listen,' that definitely makes getting the information across more difficult," Fukuda admits.

"But nonetheless I think that we still continue to try to do that and try to make countries and people aware of what the situation is. ... It makes it more challenging, but it doesn't change what we try to do.

"I think we have to remind ourselves over and over again that we are really watching something over a period of just a few months. I think we get a little bit impatient and say, 'Oh, there's no new information today so everything must be different.'

"But in fact it's just that our time horizons for observing something like this are not in sync with the real forces driving things."

Osterholm shares that view, saying people need to realize that a range of possibilities exists with this virus. It could start transmitting person to person in the near term and trigger a pandemic. But the world could also be watching it a year from now, seeing a similar pattern of cases. Or it could be like H5N1 and plague the world for a decade or more.

Another option is that the virus might disappear, though experts feel that is unlikely. And even if it did go quiet for a time, they wouldn't trust that it was truly gone.

Fukuda and Peiris were in Hong Kong in 1997 investigating the first outbreak of H5N1. Though it was feared at the time the virus was on the verge of starting a pandemic, after authorities ordered the killing of all poultry in the city the virus vanished. Five years later it emerged, and spread rapidly through parts of Southeast Asia. It has since killed millions of birds and sickened 628 people, killing 374 of them.

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