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How Easily Is Bird Flu Spread?

Study in Vietnam Shows Handling of Sick or Dead Birds Is the Biggest Risk
WebMD Health News
Reviewed by Louise Chang, MD

Jan. 9, 2006 -- Bird flu may pass more easily from poultry to people than expected, according to new research.

The finding comes from an area of Vietnam where poultry have had flu caused by the H5N1 virus. The virus has mostly been seen in birds in Asia and Europe. In rare cases, it has spread to people.

The study appears in the Jan. 9 edition of the Archives of Internal Medicine.

Global Virus

Vietnam has been hit hardest by bird flu, with 42 human deaths out of 93 confirmed cases, according to the World Health Organization (WHO).

New cases have also been reported in Turkey. Two siblings in Turkey recently died of flu caused by the H5N1 virus, according to the WHO. Both victims were children; another child in that family has also died, reportedly of bird flu, but the WHO has not confirmed H5N1's role in that child's death. According to news reports, a doctor who treated those children speculated that the kids had probably caught the virus by playing with dead chickens.

The U.S. government has urged Americans to make preparations preparations for a possible outbreak of H5N1 virus among people. So far, the H5N1 virus hasn't been reported in U.S. birds and doesn't seem to be very good at spreading between people.

Flu may spread more easily than thought from birds to people, write Anna Thorson, PhD, and colleagues. Thorson works at Karolinska University Hospital in Stockholm, Sweden.

However, no medical tests were done to check for the H5N1 virus in the study's participants or poultry.

Study in Vietnam

More than 45,400 people in a rural Vietnamese province were studied.

They were asked if they had had any flu-like symptoms within the past six months and whether they had kept or handled any poultry during that time.

Anyone who said "yes" to either question was interviewed in person.

Most people kept poultry at home, and many worked with poultry. For instance:

  • 84% lived in homes where poultry were kept.
  • About one in four (26%) lived in homes that had had sick or dead birds.
  • A third worked with manure made from poultry feces, and almost as many raised poultry for a living.

Biggest Problem: Handling Sick, Dead Birds

Handling sick or dead birds was the riskiest practice studied.

People reporting direct contact with sick or dead birds were most likely to also report flu-like symptoms. Those who had sick or dead birds at home -- but didn't touch those birds -- were less likely to report flu. Keeping healthy poultry at home wasn't linked to flu.

The flu-like illnesses were "much more mild" than confirmed human cases of the H5N1 virus in Vietnam and Thailand in 2004, Thorson and colleagues write.

Sick or dead poultry may have been responsible for 650 to 750 cases of flu-like illnesses in their study, the researchers estimate.

"The results suggest that the symptoms are most often relatively mild and that close contact is needed for transmission to humans," they write.

Thorson's team calls for studies that include lab tests to check their findings.

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