Three Neighbors of H5N1 Positive Family are Hospitalized
Recombinomics Commentary
March 29, 2005
>> Though doctors can't completely rule out human to human transmission, they believe that the family contracted the illness through direct contact with the sick birds, said Nguyen Tran Hien, director of the Institute of Hygiene and Epidemiology. Hien said final results on the tests were still pending.
"I'm not very worried (about human-to-human transmission) because they all got sick at the same time so it's more likely that they got infected from the same source,'' he said. <<
The familial cluster represented by the family of five from Haiphong is a new type of cluster. The cluster is the largest H5N1 familial cluster reported. It is the best example of a unimodal cluster, where all members develop symptoms at about the same time. Although there are only two basic types of clusters, unimodal and bimodal, official explanations of both try to use poultry as the source of the infections.
However, the poultry were never a good explanation for the bimodal clusters. The explanation could be used once of twice to suggest that the bimodal onset dates were due to two different exposures to poultry, but virtually all of the prior clusters were bimodal, and there were well over a dozen. The official count is lower because when samples were not collected from the index case, the cluster was not acknowledged, even though the secondary cases were laboratory confirmed H5N1 positive and all of the index cases died with bird flu symptoms.
Frequently the individual bimodal clusters were acknowledged as possible examples of human-to-human transmission, but always with the caveat that the cluster was a dead end, and transmission only involved close family members.
This year, clusters of clusters began to appear in Thai Binh. The poultry was blamed again, and even though the distribution of the familial clusters was bimodal, a common source of a meal or blood pudding was implicated. However, these explanations had little supporting data. Most of the data pointed away from a common source. Not only were the onset dates bimodal, but they were either too early or too late for those who developed bird flu, and someone else had the meal and developed no symptoms.
Transmission efficiencies moved forward another step when transmission went from patient to health care worker. This created a transmission chain that extended beyond the family members. The transmission chain went from index case to family member to health care worker to second health care worker. Although the second health care worker was negative, the long history of false negatives cast serious doubt on the negative data.
Data are not back on the potential large cluster in Quang Binh, but the data on the family of five in Haiphong indicate all five are H5N1 positive. Since the distribution is unimodal, a common source is suspected and again poultry is suggested. Clearly the transmission efficiency is very high, but the Kien Thuy source is still unknown.
However, now three neighbors of the family are in the hospital with bird flu symptoms. They entered within a few days of the family, raising the possibility of a larger common source.
If the eight did not have a large meal together, then the common source of poultry becomes much less likely.
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