Tracking human transmission of bird flu

Study provides first statistical evidence of limited person-to-person transmission of avian-flu virus

Photo by Dean Forbes Biostatistician Dr. Ira Longini led a study that produced the first statistical confirmation of humans contracting the avian influenza from each other rather than from infected birds.

In the first systematic, statistical analysis of its kind, infectious-disease-modeling experts at the Hutchinson Center confirm that in 2006, the avian influenza A (H5N1) virus spread between a small number of people within a family in Indonesia. The findings, by biostatistician Dr. Ira Longini and Public Health Sciences Division colleagues, appear online and in the Sept. 1 print edition of Emerging Infectious Diseases, a journal of the Centers for Disease Control and Prevention.

Co-authors on the paper were biostatisticians Drs. Betz Halloran and Yang Yang, and epidemiologist Jonathan Sugimoto, a predoctoral research associate at the Statistical Center for HIV and AIDS Research and Prevention. All are part of the Center's Vaccine and Infectious Disease Institute.

The researchers based their findings on a cluster of eight avian-flu cases within an extended family in northern Sumatra. Using a computerized disease-transmission model that took into account the number of infected cases, the number of people potentially exposed, the viral-incubation period and other parameters, 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, infected, most likely through exposure to dead poultry and chicken feces. Genetic-sequencing data supports the possibility that the boy then infected his father. Statistical data validates other person-to-person transmissions in the cluster. All but one of the flu victims died, and all had sustained close contact with other ill family members prior to getting sick — a factor considered crucial for transmission of this particular flu strain.

The methods and software used in this research led to the development of a software application called TranStat, which will allow first responders to enter, store and perform real-time analysis of data from infectious-disease outbreaks. This tool soon will be available online free via MIDAS, the Models of Infectious Disease Agent Study, which is supported by the National Institute of General Medical Sciences.

"TranStat will prompt people to gather precisely the data that needs to be collected to better understand and contain any infectious-disease spread, not just the avian flu," Sugimoto said.

The National Institute of General Medical Sciences MIDAS network and the National Institute of Allergy and Infectious Diseases funded and supported the study.

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