Monday, December 27, 2004

Bird flu danger signal from Japan

In an earlier post I wrote finis to the cases of avian influenza in workers involved in a massive chicken cull in Japan last February. Five people were found to have immunologic evidence of H5N1 infection after the fact, and one worker, for whom paired sera were available, showed a greater than four-fold rise in antibody titer. The only reported symptoms were a sore throat in one worker. Because of the close contact with infected birds there was no evidence that the virus had changed character with respect to person-to-person transmission. It was also an event that occurred ten months ago. But an editorial in the Japanese daily Yomiuri Shimbun (Tokyo) has made me rethink this easy dismissal and prompted one last comment. It is not a happy one.

The Editorial raises the (excellent) question of why it took from February until mid-December to report on these cases. It also claims these five workers (four farm employees and a Kyoto prefectural employee who inspected the farm) wore no "flu masks", protective clothing and took no antivirals, contradicting earlier reports that all had worn personal protection and were treated prophylactally with oseltamavir, an antiviral. Even more troubling is this:
The [Health, Labor and Welfare Ministry] said it took a long time to convince the employees to allow blood samples to be taken and to develop a fool-proof method of detecting the virus. In total, about 7,000 people were engaged in containing the epidemic, but only 58 of them were tested for the disease.
This indicates that 10% of the tested workers were infected but less than 1% were tested. Even if we assume there was no serious illness among the unexamined 99%, if their infection rate were the same as those tested we would expect infections in about 700 and symptoms in over 100. There is thus the potential that a certain number of these could also be co-infected with a human-adapted strain of influenza A, increasing the danger of producing a dangerous recombinant with an H5 protein adapted to person-to-person transmissibility.

These data underscore the importance of providing personal protective equipment to workers engaged in the mass culling of infected birds in southeast asia where the disease is spreading and also treating them prophylactically with effective antivirals. When a vaccine becomes available they should be the first vaccinated.

Upon further reflection this case raises serious questions about the safety of efforts to contain the disease before it reaches the human population. It would indeed be a heavy irony if this were the pathway to a global pandemic.