Lab tests can miss bird flu, expert warns

PUBLISHED : Saturday, 17 December, 2011, 12:00am
UPDATED : Wednesday, 06 May, 2015, 4:29pm


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Lingering bird flu infections in recovering patients could be missed by laboratory tests, leaving the patients vulnerable and a potential source of infection in the community, a microbiologist warned yesterday.

The warning came from the deputy director of Chinese University's Stanley Ho Centre for Emerging Infectious Diseases, Professor Paul Chan Kay-sheung, who said the tests could miss the H5 virus as the viral load - a measure of the severity of a viral infection - dropped.

He said Hong Kong should not lower its vigilance against the H5 virus even after an 11-year-old boy and his 48-year-old mother suspected of having bird flu both tested negative for the virus.

'The [viral] load of H5 in humans is usually not as heavy as human flu, making it more difficult to detect, especially for patients who show only mild symptoms or have their symptoms subsiding,' he said.

'Therefore, the health authorities should continue their investigation to ensure the pair did not contract avian flu.'

He said that testing their antibodies after two weeks would be a more accurate method.

The Health Department confirmed yesterday that the 11-year-old boy admitted to Princess Margaret Hospital on Thursday for isolation with a ever and a cough had tested negative for bird flu. On Thursday, his mother, a school clerk at the Chiu Lut Sau Memorial Secondary School in Yuen Long, also tested negative for the virus.

The mother developed a fever, a sore throat and diarrhoea on Wednesday, a day after she picked up a sick bird on the school campus with her bare hands and without wearing a face mask. It sparked fears of an H5 infection after the bird later died and tested positive for the virus.

But the Health Department said the woman's specimen was obtained on the second day after she started to develop symptoms, when the viral load should have been high enough for testing. The department also said it would not test for antibodies in either case.

The boy's school was closed yesterday for disinfection.

Chan said bird flu remained a global threat to humans, especially in Southeast Asia, and the danger had not eased. Even though infections of the known killer strain, H5N1, remained sporadic, six in every 10 patients who contracted the virus die. Since 1997, 342 people have died from H5N1.

Chan did not rule out the possibility that pair had come down with human flu. He said the flu season this year had started two months earlier than usual. He said the two peak seasons for human flu were normally in February and in July, but the winter peak season had already begun this month.