September 29, 2004
Probable Case of Human-to-Human H5N1 Transmission: Thailand
On September 28th, the WHO reported that the Thailand Ministry of Public Health has concluded that the death on September 20th of a 26-year-old woman due to H5N1 avian influenza virus “represents a probable case of human-to-human transmission” of the virus.
The index case of the H5N1 transmission appears to have been the 11-year-old daughter of the 26-year-old woman. This child died of an influenza-like illness on September 8. The 11-year-old girl lived with her 32-year-old aunt, who has also been diagnosed with lab-confirmed H5N1 infection and has been hospitalized. A fourth ill family member is a 6-year-old son of the aunt. He is also hospitalized and is being tested for H5N1 infection. The WHO Influenza Laboratory Network is currently sequencing these H5N1 isolates to see if they have mutated in some way that might facilitate human-to-human spread.
That limited, non-sustained transmission of H5N1 from person-to-person would occur in 2004 is not surprising given that transmission resulting in antibody-positive, asymptomatic infection occurred with the initial H5N1 outbreak in 1997 in Hong Kong. Of much greater public health concern would be the unprecedented person-to-person transmission of H5N1 that is sustained, especially if it begins to approach the efficient transmission seen during the yearly outbreaks of human influenza A H3N2 or H1N1. So far, this has not happened.
The Thailand Ministry of Public Health has responded admirably to the recent H5N1 situation, opening an avian influenza Operational Center to respond to questions and address all aspects of avian influenza. Moreover, nationwide they have instituted a very large and coordinated response effort involving thousands of workers to provide surveillance for H5N1 and testing for anyone with influenza-like disease. A very informative and detailed listing of case definitions (suspect, probable, confirmed) and individual case evaluations, by location across the country, is provided daily on the Ministry of Public Health website at http://eng.moph.go.th
Daniel R. Lucey, MD, MPH
Director, Center for Biologic Counterterrorism and Emerging Diseases