Probable Case of Human-to-Human Bird Flu Transmission Reported

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The H5N1 viruses sampled from the father and the son were virtually genetically identical.

The father received antiviral treatment as well as plasma from an individual who had been vaccinated against the virus as part of a vaccine trial. The son was diagnosed too late to receive appropriate treatment.

All 91 exposed contacts, including the son's girlfriend and mother, tested negative for H5N1.

Transmission may have occurred if the father inhaled droplets coughed out by his son, or by contact with the son's clothing that was contaminated with fecal matter. The father wore a surgical mask during his last visit with his son but had not worn protective gear before that, the report stated.

Interestingly, no outbreaks of H5N1 in poultry were identified in Nanjing, a city in eastern China, before or after these two human cases. No sick or dead poultry were seen either, the report said, adding that it's also important to note that this case of son-to-father transmission has not been proven yet.

According to the study authors, more than 90 percent of H5N1 clusters in humans have occurred in blood-related family members.

And, experts said, this latest case is no reason for alarm.

Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, which funded the study, said, "This is not something new. Limited human-to-human transmission has been seen intermittently for years and years. This is just another example among a few. It's what we call a dead-end person-to-person transmission."

He added, "What we worry about is secondary and tertiary transmissions, when someone gives it to someone who gives it to someone. That is not the case here."

"I took great reassurance from this study," Alcabes added. "Very, very occasionally, you can get limited transmission of the avian virus from one infected human to another human, but it seems only to happen in families. There's nothing here to suggest new reasons to worry, let alone panic."

Added Dr. Pascal James Imperato, chairman of the department of preventive medicine and community health at SUNY Downstate Medical Center in New York City, "There's no proof positive that the father was not independently exposed to poultry."