Earlier Human to Human Bird Flu Transmission in Vietnam
Recombinomics Commentary
February 4, 2005
A review of the initial bird flu cases in Vietnam identifies three additional family clusters. In the earliest cluster, the disease onset date for the index case is not available. However, the time differential between the dates of death for the two siblings is 17 days, suggesting human to human transmission. The other two cases, like the more recent 6 familial clusters, all involve a disease onset date differential of a week or more for family members and all clusters included at least one H5N1 laboratory confirmed case.
These cases would indicate that the likely human to human transmission in the more recent cases is not a new development, but the frequency of the recent cases may be higher. The frequency is difficult to calculate, because in many of these clusters, individual cases either were not tested or were initially negative or inconclusive. Therefore, similar cases that are not in suspect clusters may not be included in reported cases. The three clusters below indicate all 9 reported familial clusters involve likely human to human transmission, rather than infections from common sources.
The WHO official tally for the 9 clusters (7 in Vietnam, 1 in Thailand, 1 in Cambodia) is as follows:
13 fatalities, 2 recoveries.
The evidence for human to human transmission in the 9 clusters suggests 1 likely, 1 possible, 2 under investigation.
The same 9 clusters generate the following if a 7 day time differential (disease onset in 8 clusters and disease death in the 9th cluster) is used, and fatalities in the cluster are considered H5N1 avian influenza cases:
18 fatalities, 2 recoveries, 1 in critical conditin Jan 22, all 9 clusters involve human to human transmission.
The details for the 3 earlier clusters are below:
Nam Dinh Cluster
Index case, 7F died December 29, 2003 of a respiratory illness. No samples collected. Her 5 year old brother developed symptoms December 22, 2003, was admitted to the hospital December 30, 2003, and died January 15, 2004. He tested positive for H5N1.
Ha Nam Cluster
Index case (12F) developed symptoms December 25, 2003, admitted December 27, 2003 and died December 30, 2003. Her mother developed symptoms January 1, 2004, was admitted January 5 and died January 9. Both were H5N1 positive.
Thai Binh Cluster
Index case, Ngo Le Hung, 31M developed symptoms January 3, 2004, was admitted January 6 (or 7th), died January 12. No sample collected. His two sisters (23F, 30F) provided care and both developed symptoms Jan 10, both were admitted Jan 13 and both died Jan 23. Both were H5N1 positive, although initial tests were inconclusive. The wife of the index case, 28F was also admitted on Jan 13, but did not develop symptoms and was not tested, so she is not included in the totals.