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Differences in Bird Flu Case Fatality Ratios in Vietnam

Recombinomics Commentary
February 7, 2005

>> Pham Van Quy, 66, from Hanoi, and Han Ngoc Manh, 30, from Hung Yen northern province, have fully recovered and are in good health, said doctors at the Hanoi Institute of Tropical Diseases. 

The institute had previously released three other bird flu patients, including Bui Van Ha and brothers Nguyen Thanh Hung, 42, and Nguyen Manh Hung, 36.

Since late December 2004, five of the seven patients who had contracted the deadly H5N1 virus strain in northern Vietnam had been discharged and the two other victims died. <<

The discharge of two more H5N1 patients from northern Vietnam enhances the difference in outcomes in the north and southern regions.  Although Mguyen Manh Hung was considered unconfirmed by WHO, in part because he did not develop symptoms, there have been 4 additional discharges within the group of 6 confirmed cases.  Thus, the case fatality rate is 33% in the north (and lower if the seventh case is confirmed).  In contrast none of the patients in the south, in Vietnam and Cambodia, have been discharged.

The difference in case fatality ratios may reflect differences in the sequences of the isolates,  Novel sequences had been noted this season in Hong Kong in isolates from Grey Herons and some genetic drifting in the Vietnam isolates has been noted.

There also has been some difference in familial clusters.  There was one in the north and one or two members have recovered, depending on the final disease status of the youngest brother.  If he is confirmed to be positive, then he was probably infected by the duck that he helped slaughter or he was infected by one of his two older brothers, since he did not eat the blood pudding.  The blood pudding is an unlikely source of infection because the brother-in-law of the index case did  not develop symptoms or test positive.  Moreover, disease onset was too early for the index case and too late for the middle brother.

Human to human transmission would be consistent with the bimodal distribution of disease onset dates, which was also present in all other 8 clusters in Vietnam, Thailand, and Cambodia.

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