As swine flu continues to spread around the globe, a clearer and in some ways more unnerving picture of the most serious cases has started to emerge, indicating that the virus could pose a greater threat to some young, otherwise vibrant people.
The virus can cause life-threatening viral pneumonia much more commonly than the typical flu, prompting the World Health Organization to warn hospitals to prepare for a possible wave of very sick patients and to urge doctors to treat suspected cases quickly with antiviral drugs.
Experts stress that most people who get the H1N1 virus either never get sick or recover easily. But some young adults, possibly especially women, are falling seriously ill at an unexpectedly rapid pace and are showing up in intensive care units and dying in unusually high numbers, they say.
Although why a minority of patients become so sick remains a mystery, new research indicates that H1N1 is different from typical seasonal flu viruses in crucial ways — most notably in its ability to penetrate deep into the lungs and cause viral pneumonia.
“It##s not like seasonal influenza,” Nikki Shindo of the World Health Organization said. “It can cause very severe disease in previously healthy young adults.”
So far, the virus does not seem to sicken or kill people more often than the typical flu. But the pattern of people getting seriously ill is far different than in typical flu seasons. The elderly, who are usually most vulnerable, are generally spared; children, teenagers, pregnant women and young adults are the most common victims.
Officials have been closely monitoring the virus for signs it has mutated into a more dangerous form, and they have also been testing animals for the virus because of fears that infected livestock could cause more-lethal mutations.
Seasonal flu viruses tend to infect primarily the upper respiratory system. But recent animal studies and autopsies on about 100 swine flu victims show that H1N1 infects both the upper respiratory tract, which makes it relatively easy to transmit, and also the lungs, which is more similar to the avian flu virus that has been circulating in Asia.
About a third of patients who required intensive care had bacterial pneumonia, but H1N1##s proclivity to infect lung cells makes it more likely than seasonal flu to cause viral pneumonia, which can lead to life-threatening lung damage.
Although it remains unclear how frequently the virus makes people seriously ill, recent reports from Mexico, Canada, the United States, Australia and New Zealand indicate that perhaps 1% of patients who get infected require hospitalization. Between 12 to 30% of those hospitalized need intensive care, and 15 to 40% of those in intensive care die.
While about two-thirds of U.S. patients who were hospitalized in the spring had other medical conditions, the CDC reported last week that an analysis of more than 1,400 hospitalized victims found perhaps half had no serious health problems.
About one-third of those around the world who have died or became seriously ill from swine flu appear to have been vulnerable because they had heart or lung disease, chronic kidney problems, or other ailments that usually put people at risk. But others had conditions that many may not immediately associate with frailness, such as mild asthma, high blood pressure, high cholesterol and obesity.
There appears to be no way to predict with certainty who may suffer serious, life-threatening complications, since some victims have had no other health problems.
For instance, Stacey Hernandez Speegle, 30, of Madison, Calif., who died in July, “was in great shape. She was on the softball team. She had two young children. She was renovating her house,” said her mother, Tamara Brooks. “It##s just so hard to believe.”
Although it has been well publicized that pregnant women appear to be at increased risk, some evidence has started to suggest that being female may itself be a risk factor, for reasons that remain unclear.
“There##s no question that women, and particularly young women, are getting hit disproportionately,” said Kumar. He noted that women tend to have more fat tissue, which can help stimulate a dangerous inflammatory response to infections.
And some of those who develop serious illness deteriorate soon after starting to feel ill. They require oxygen masks, ventilator machines to pump oxygen into their lungs to keep them alive, and drastic, often rarely used measures to try to save them within days of the first fever, ache or cough.
“The rapidity of it is striking,” said Andrew R. Davies, deputy director of intensive care at Alfred Hospital in Melbourne, Australia.
Some of the cases in Australia and New Zealand were so severe that doctors resorted to a much more aggressive, less commonly used treatment known as extracorporeal membrane oxygenation (ECMO). It involves siphoning patients## blood into a machine to remove carbon dioxide and then infuse it with oxygen before returning it to their bodies.
Other doctors have tried administering nitric oxide and putting patients in a bed that turns them upside down to help their lungs work better.
At least 86 Americans younger than 18 who have died from H1N1. About half of the deaths in the past month were among teenagers. Since Aug. 30, 43 pediatric deaths have been reported, including three in those younger than age 2, five among those ages 2 to 4, 16 in those ages 5 to 11, and 19 among those ages 12 to 17.
At least 2,914 Americans have died from flu-related illnesses since the H1N1 began, the CDC said.
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The Washington Post (abridged)