CDC’s Influenza A H5N1 Hong Kong Field Investigation Wraps Up, Results Anticipated in Six Weeks

CDC scientists working with the Hong Kong Department of Health (HKDH) have concluded nearly 2 months of field data collection as part of the World Health Organization’s investigation of the influenza A (H5N1) avian virus capable of infecting people.

The last members of the CDC team return to the United States this week to begin in-depth data analysis. CDC expects to provide results from the multiple studies to the HKDH in February. The HKDH and CDC had hoped to release some preliminary findings before the CDC field team’s end-of-January departure from Hong Kong. However, the volume and scope of laboratory work at CDC on blood samples needed to analyze questionnaire data was greater than first expected, and is taking longer than anticipated.

The CDC influenza A (H5N1) investigation including 10 separate cohort studies and one care-control study. In addition, serum specimens were collected from family members of persons who were confirmed with H5N1.

“We have two critical questions to answer and hope that the data we’ve collected will give us those answers,” said the CDC field investigation team leader in Hong Kong, Dr. Keiji Fukuda. “We are looking for evidence of human-to-human transmission of the H5N1 virus. And, we hope to identify any risk factors and any behaviors that may put someone at greater risk for contracting the virus.

“These sound like simple questions, “ continued Fukuda, “ but to find scientifically sound answers may be difficult. Whatever results we discover, even if the primary questions remain unanswered for now, will be shared first with the Hong Kong Department of Health.”

During the field investigation of 17 cases that occurred in November and December, HKDH, hospital professionals, and CDC medical officers collected approximately 3,300 blood samples from 2,897 study volunteers. Study groups included people with confirmed H5N1, people with possible contact with H5N1 patients, people who had contact with poultry, and people with demographic characteristics similar to exposed groups but with no relationship to H5N1 patients. More than one blood sample was taken from some persons involved in the studies.

Between May and December 1997, a total of 18 confirmed human cases of influenza A (H5N1) occurred in Hong Kong. The first-ever reported case of an avian influenza virus directly infecting a person occurred in Hong Kong in May. The HKDH invited CDC scientists to work with them to investigate additional human cases of H5N1 that occurred in November and throughout December. Heightened surveillance for H5N1 cases in Hong Kong and at other WHO surveillance sites around the world will continue while CDC analyzes data regarding the 18 confirmed cases.

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