Doctors on scene were mumbling about this when it happened. Now researchers at the Fred Hutchinson Cancer Research Center confirm that the avian influenza A (H5N1) virus spread between a small number of people within a family in Indonesia in 2006. Using a computerized disease-transmission model that took into account the number of infected cases, the number of people potentially exposed, and the viral-incubation period, the researchers produced the first statistical confirmation of humans contracting the disease from each other rather than from infected birds.
The cluster contained a chain of infection involving a 10-year-old boy who probably caught the virus from his 37-year-old aunt, who had been exposed to dead poultry and chicken feces, the presumed source of infection. The boy then probably passed the virus to his father—a possibility supported by genetic sequencing. Other person-to-person transmissions in the cluster were backed up with statistical data. All but one of the flu victims died, and all had had sustained close contact with other ill family members prior to getting sick—a factor crucial for transmission of this particular flu strain.
“The containment strategy [quarantine] was implemented late in the game, so it could have been just luck that the virus burned out,” said lead author Ira M. Longini Jr. “It went two generations and then just stopped, but it could have gotten out of control. The world really may have dodged a bullet with that one, and the next time we might not be so lucky.”
The researchers estimate the risk of one infected person passing it to another to be 29 percent—a level of infectiousness similar to seasonal influenza A in the United States. They also assessed another large avian-flu cluster in eastern Turkey with eight infected people in 2006, four of whom died. In this case, there was no statistical evidence of human-to-human transmission—though that was most likely due to a lack of sufficient data. “There probably was person-to-person spread there as well but we couldn’t get all the information we needed for the analysis,” said author, Yang Yang.
After near hysteria, the media’s gone Rip Van Winkle on this one. Not a good idea. The problem has not gone away. JULIA WHITTY
