Misdiagnosis raises questions about extent of avian flu epidemic

BMJ 2005; 330 doi: (Published 24 February 2005) Cite this as: BMJ 2005;330:437
  1. Jane Parry
  1. Hong Kong

    The illness of a Vietnamese boy who died from the H5N1 strain of avian influenza last year was not correctly diagnosed at the time because he had not developed the severe respiratory symptoms normally associated with the disease.

    That the actual cause of his death was not identified at the time suggests that the prevalence of avian flu in South East Asia was underestimated, experts from the World Health Organization say.

    The 4 year old boy was admitted to hospital on 12 February 2004 with severe diarrhoea. An x ray film of his chest was normal. Three days later he became drowsy and developed respiratory symptoms, then lapsed into a coma. He died on 17 February from encephalitis of unknown origin.

    However, according to findings published last week in the New England Journal of Medicine (2005;352: 686-91), specimens of the boy's cerebrospinal fluid, faeces, and blood all subsequently tested positive for H5N1. The boy's 9 year old sister had died from a similar illness two weeks earlier, but no samples were available for testing. Neither child had respiratory symptoms when they were admitted to hospital.

    “Encephalitis is endemic in Vietnam. How many of those cases are masking bird flu? We take this very seriously,” said Peter Cordingley, WHO's spokesman in Manila. “In the countryside, cases may not even reach the hospital. We don't know how widespread the avian flu virus is. We don't think we will revise our case definitions, but it will change the way we look for the disease,” he added.

    Neither of the children had been in contact with sick chickens. The family kept fighting cocks, which were asymptomatic but culled anyway. Ducks in the area, which were also asymptomatic, could have been the cause of the infections.

    “The threat from ducks is a real concern, because ducks are more likely to have asymptomatic infection,” said Professor Paul Chan of the Department of Microbiology at the Chinese University of Hong Kong. “Usually water birds adapt more easily than land based birds to new variants of influenza, so ducks can be asymptomatic yet shed a large amount of infectious material. Surveillance for H5N1 bird flu relies on seeking out sick birds, so to some extent the threat from ducks may have been overlooked.”

    WHO has sent in experts at the request of the Vietnamese government. Laboratory technicians were sent to Ho Chi Minh City and Hanoi, and Dr Rick Brown, a British specialist in public health, is currently in Vietnam working on surveillance and epidemiology.

    The UN Food and Agriculture Organization and the World Organization for Animal Health jointly hosted a meeting this week, in collaboration with WHO and the Vietnamese government, in Ho Chi Minh City. The meeting brought together chief veterinary officers, expert scientists, and representatives of the UN and donor organisations to discuss the current H5N1 avian flu situation in Asia. The meeting was part of a response to the Vietnamese government's request for help from the UN in formulating a long term strategy to eliminate the virus in poultry and in coordinating international aid.

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