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Medical Journal

What we know about H1N1 flu
Scripps Howard News Service


October 01, 2009

Since bursting onto the world health stage last spring, the novel H1N1 flu has become one of the most-studied pathogens ever.

Scientists have tracked how it spreads, how it infects, how it behaves in animal and human hosts, the symptoms it creates and why some people have much nastier experiences with it than others.

Some of the findings have overturned early assumptions; many others have raised new questions about how to detect and treat the first worldwide flu to strike in 30 years.

No matter how severe the outbreak turns out to be, researchers will continue working for years to understand the new strain.

Here's a sampling of the research findings thus far:

-- The first known cases did not occur on or near pig farms. Mexican epidemiologists have found evidence that the first human infections from the new strain happened in central and northern Mexico in early March. "Patient Zero" was probably a 6-month-old girl who had no apparent contact with pigs. Pigs, by the way, have been getting the swine flu on a few farms, as have some farmworkers, but so far it still appears swine have more to fear from people with flu than the other way around.

-- Weather patterns may help fuel flu pandemics, say scientists at Texas A& M University. They note that a very strong El Nino event in 1918-19 caused severe drought over much of India, where as many as 17 million people died from the worldwide flu outbreak. The winter and spring were unusually cold across North America that year, likely contributing to the epidemic there. An El Nino episode of unusually warm water is under way in the eastern Pacific now.

-- Being a high-risk patient is only part of the story. French researchers who studied about half the known swine-flu deaths as of midsummer found that just over half the people who died were either pregnant or had underlying health conditions, particularly diabetes and conditions linked with obesity. But 51 percent of the deaths were in patients with no apparent health issues before the flu. A separate Spanish study found a similar pattern.

-- Older people may be less likely to catch the new flu virus, possibly due to past exposure to similar strains. But French and British studies suggest that when people over 60 do come down with H1N1, they have more severe disease, and anyone with heart disease or respiratory problems is in particular danger.

-- Some people who get severely sick from this flu have a deficiency of a particular immune-system antibody, Australian researchers found in a study of pregnant women.

-- The new swine flu can infect cells deep in the lungs, along with cells in the nose, throat and upper airways. Seasonal flu usually infects just the upper respiratory tract. British scientists say the new virus still doesn't seem to bind to receptors in the lungs as strongly, but infecting more cells makes for a more serious illness.

-- Drug-resistant swine flu is rare. Worldwide, health officials have found only about two-dozen cases where the virus was resistant to oseltamivir -- Tamiflu. Scientists think that, in most cases, the resistance developed in a patient who had either taken the drug as a preventive earlier or after becoming infected. So far, there is no indication that the virus has mutated to evade anti-flu drugs in any widespread fashion.

-- Swine flu doesn't always come with a fever. Reports from Mexico and Chile suggest that only about half the cases studied over the spring and summer had any measurable fever. That makes the illness both harder to diagnose and harder to give an all clear for. With standard flu, a spike in fever punctuates the illness, and infected people are most contagious just before and after that point. So most guidelines say a return to work or school is OK after one or two fever-free days.

-- People may shed swine-flu virus for a longer time than seasonal flu. Mexican studies suggest it's possible to share the bug for a week or longer after symptoms start. Although covering a cough or sneeze is important, researchers have also noted that the virus tends to linger on surfaces, including computer keyboards and other electronics, so not only hand-washing but also sanitary wipes may be a good idea if anyone in the house, office or classroom has had a flu-ish illness in the past week.


Contact Lee Bowman at BowmanL(at)
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