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Biosecurity BriefingH5N1 Family Clusters and Limited Human-to-Human Transmission Found in China and Pakistan By Michelle Cantu, April 11, 2008 On April 8, 2008, the Lancet published results from investigations by Chinese health officials into the 2007 H5N1 influenza family cluster in Jiangsu Province, China. In this cluster, possible human-to-human transmission of the H5N1 virus occurred between two members of a family, who both tested positive for H5N1 virus. The index case, a 24 year old male, is thought to have contracted the virus at a live poultry market; however, the second case (the man’s 52 year old father) had no contact with infected poultry. His only exposure to the virus appears to be through contact with his ill son. According to the article, it cannot be ruled out that the father's exposure to the virus occurred through other means. However, genomic sequencing has shown that both cases were "identical except for one…nucleotide substitution," and that “all [virus] genes were entirely of avian origin.”1 During the investigation, 91 close contacts of one or both cases consented to serological testing and all were negative for H5N1 antibodies. The son died five days following hospitalization and on the same day that H5N1 was confirmed by RT-PCR. According to the Lancet article, the father had provided unprotected bedside care for prolonged periods of time and did not wear personal protective equipment until after the confirmation of H5N1. The father received oseltamivir and later two plasma transfusions from a clinical trial patient that had been vaccinated for H5N1 virus.1 According to the article, human H5N1 “clusters have occurred in 1997 and 2003 in Hong Kong…and in 2004–2007 in Indonesia, Turkey, Azerbaijan, Vietnam, and Thailand.” Researchers also note that “limited person-to-person transmission…has been strongly suggested in the largest cluster of Indonesia and in Thailand.” Moreover, the article suggests that more research is needed on “potential genetic susceptibility to H5N1 virus infection” due to the fact that “more than 90% of H5N1 care clusters have occurred in blood-related family members.”1 In an article in BBC News, Ian Jones, Professor of Virology at University of Reading, noted that since the father and son were the only people infected, “the virus had not changed to indicate adaptation to human infection” and he concluded that “[t]here is no indication from this data that we are nearer [to] a pandemic.”2 In other news, on April 3, 2008, the World Health Organization (WHO) confirmed the presence of H5N1 in two additional members of a family cluster in Peshawar, Pakistan. The laboratory tests conducted by the WHO H5 Laboratory in Cairo, Egypt, and the WHO Collaborating Center for Reference and Research on Influenza in Atlanta, Georgia, supported positive H5N1 results from the December 2007 outbreak investigation of the family cluster. The data suggests that there was probably limited human-to-human transmission among family members. The findings also confirm that there is “no evidence of sustained or community human-to-human transmission” and that “all identified close contacts including the other members of the affected family and involved healthcare workers remain asymptomatic and have been removed from medical observation.”3 References
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