Evidence for H5N1 Human to Human Tranmission in Pakistan
Recombinomics Commentary
December 18, 2007
The eight suspect human bird cases in Pakistan are likely a combination of infections from poultry and limited person to person transmission due to close contact, a top World Health Organisation expert said on Tuesday. Keiji Fukuda, coordinator of WHO's global influenza programme, said while unconfirmed, any human to human spread seemed similar to previous outbreaks in Thailand and Indonesia -- affecting close family members caring for sick loved ones.
Eight people have tested positive for the H5N1 bird flu virus in North West Frontier Province since late October, and one of the confirmed cases has died. A brother of the dead man also died, but was never tested, so is not counted among them.
The "index" case, who recovered, is a veterinarian who helped with culling operations and it is his two brothers who died after taking care of the ill man, according to Fukuda.
The above comments confirm the consensus media reports and leave little doubt that the large familial H5N1 cluster in Pakistan involved human to human (H2H) transmission. Similar transmission may also be present in the smaller familial cluster. The clustering of clusters is cause for concern, as is the size of the larger cluster, which involves the index case, four brothers, a cousin, and possibly a health care worker and a brother residing in Nassau county, New York. Although the brother in New York tested negative in the United States, the use of Tamiflu on patients prior to the collection of samples raises concerns of false negatives. Similarly, reports that a health care worker also tested positive, raises concerns that the transmission chain is the longest reported to date for H5N1.
The consensus media reports indicated the veterinarian was the index case for the larger cluster. He organized a cull on October 21-23 and developed symptoms on October 25. Disease onset dates have not been released, but media reports indicate the two brothers died on November 19 and 29. The spread between the disease onset date of the index case and the later date of death for the H5N1 confirmed brother supports one or two rounds of human-to-human transmission. Moreover, the lab confirmation of H5N1 in the health care workers suggests the transmission extended outside of the family members. The disease onset dates for the other two brothers and cousin are unknown, but those dates may support additional chains of H2H transmission.
The long delay between initial the initial onset date of October 25, and more details on onset dates remains a cause for concern. Efficient H2H transmission is the chief concern with regard to an H5N1 pandemic, and these delays, as well as collection of samples after the stat of Tamiflu treatment, limit the analysis of transmission and monitoring of H5N1 spread.
Details on disease onset dates, Tamiflu treatment dates, and sequence data, would be useful.
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