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Invisible Human to Human Bird Flu Transmission in Vietnam
February 2, 2005
>> The rate of confirmed human cases this winter, two or three a week, is similar to the rate last winter, said Dr. Peter Horby, an epidemiologist with the World Health Organization in Vietnam.
There was one case of probable human-to-human transmission in Thailand last August, and two clusters of cases in families here in Vietnam since late December are now under investigation. But most cases still appear to be caused by close contact with live, infected poultry, or by consumption of the blood of raw poultry.
Many of the human victims of bird flu this winter, as last winter, have been treated at Bach Mai Hospital's institute for tropical diseases in Hanoi. The hospital is elite by Vietnamese standards but spartan and with limited equipment by the standards of developed countries. Dr. Nguyen Hu Tuong Van, deputy director of the emergency department and head of bird flu treatment, said local laboratories were unable to analyze samples quickly to determine whether patients had bird flu. <<
It is quite clear that the "official" WHO numbers understate the bird flu situation in Vietnam, including human to human transmission of H5N1 avian influenza. The testing is clearly lacking. Some samples are not collected, some are not collected properly, and some are simply false for unknown reasons. Testing of multiple samples in a patient reduces the number of patients who are misclassified, but for cases where there are no samples collected, application of a small amount of logic and probability is useful. Unfortunately, the testing / collection is so inadequate that the official numbers cited by WHO in media reports are at best misleading.
The number of reported human H5N1cases in Vietnam is still quite low. When two of more family members develop bird flu symptoms and one or more is a laboratory confirmed positive, then it is quite reasonable to assume that each of the fatal cases in the cluster is a bird flu case. Moreover, when the time differential between the onset of symptoms is a week or more, the disease transmission is likely to have been human to human.
These very basic criteria identify six clusters of human to human transmission since July, one in Vietnam and one in Thailand over the summer. The remaining four, one in Cambodia, and three in Vietnam, are since December.
Briefly, the six clusters involved 14 patients. Each cluster had at least one patient tested. Of the 14 patients, 9 were tested and all were H5N1 positive. Only three (2 discharged, 1 was in critical condition on Jan 22) of the 14 patients survived. Of the five clusters in Vietnam / Cambodia, four were in or adjacent to the Mekong Delta (Hau Giang, Dong Thap, Bac Lieu, and Kampot Cambodia).
Ignoring these likely human to human transmissions of H5N1 avian influenza is hazardous to the world's health.