Bird flu may be more common, less deadly

Seattle Post-Intelligencer
Jan. 09, 2006

CHICAGO -- As bird flu cases rise at a disturbing pace in Turkey, new research offers a bit of hope - it's likely that many people who get it don't become seriously ill and quickly recover.

Although not definitive, the new study suggests the virus is more widespread than thought. But it also probably doesn't kill half its victims, a fear based solely on flu cases that have been officially confirmed.

"The results suggest that the symptoms most often are relatively mild and that close contact is needed for transmission to humans," wrote Dr. Anna Thorson of Karolinska University Hospital in Stockholm and colleagues who conducted the study. It was published in Monday's edition of Archives of Internal Medicine.

So far, the bird flu deaths in Turkey involved children playing with dead chickens.

The new study involved 45,476 randomly selected residents of a rural region where bird flu is rampant among poultry - Ha Tay province west of Hanoi. More than 80 percent lived in households that kept poultry and one-quarter lived in homes reporting sick or dead fowl.

A total of 8,149 reported flu-like illness with a fever and cough, and residents who had direct contact with dead or sick poultry were 73 percent more likely to have experienced those symptoms than residents without direct contact.

The researchers said between 650 and 750 flu-like cases could be attributed to direct contact with sick or dead birds. While most patients said their symptoms had kept them out of work or school, the illnesses were mostly mild, lasting about three days.

By contrast, most of the more than 140 cases linked to bird flu and reported to the World Health Organization since January 2004 have been severe - killing more than half the patients.

Dr. Frederick Hayden, a bird flu specialist at the University of Virginia, said the study "is useful for hypothesis generation" but highlights the need for widespread blood testing in Asia to determine the true incidence of bird flu in people.

The study authors noted that without any blood-test evidence to prove that the Vietnamese residents had bird flu, the results are only suggestive and far from conclusive.

Still, other flu experts called the study compelling.

"I would call this the smoking gun," said Dr. Gregory Poland, a Mayo Clinic flu specialist. "All of us have been concerned and have guessed that the data we have so far has been the tip of the iceberg."

The human cases counted so far likely have been the most severely ill patients treated at major hospitals, Poland said.

"In the really rural areas, we know that this had to be occurring" too, and the study suggests that the prevalence "is pretty high," he said. "The data lines up biologically the way we would have expected it to."

The researchers can't be certain that the birds reported in the study had been felled by the H5N1 virus or that it caused the human illnesses, but that is the most likely explanation given the ongoing epidemic in Asian poultry, Thorson said.

"The closer the contact with sick or dead poultry, the higher the risk for flu-like illness," Thorson said. That finding "speaks strongly against it being a circumstantial finding."

The H5N1 strain has ravaged flocks in at least 16 mostly Asian countries since late 2003 and is starting to spread to birds in Eastern Europe.

The news would be double-edged if the researchers' suspicions are correct, Poland said. While more widespread prevalence of bird flu in people would be worrisome, "the good news would be that virtually all of these were mild illnesses and everybody survived," he said.

The deadliness of reported bird flu cases "has been one of the features that has galvanized international interest" and stoked concerns that it could turn into a pandemic, said Dr. William Schaffner, a flu expert at Vanderbilt University.

But if the study is accurate, its findings would be "entirely consistent with the way most infectious disease occurs," Schaffner said.

While conventional human flu is thought to contribute to some 36,000 deaths yearly in the United States alone, many more people develop mild illness. Even in past flu epidemics, fatality rates generally were around 2 percent, Schaffner said.

The study may help temper "some of the overblown statements" about the deadliness of bird flu if the results can be confirmed by blood testing, he said. "It's a bit of a nice reality perspective."