Kwok Hang Mak, M.B., M.Sc.

Consultant, Community Medicine, Department of Health Hong Kong Special Administrative Region, People's Republic of China

In recent years, the Hong Kong Special Administrative Region of the People's Republic of China has witnessed, like other parts of the world, the emergence and reemergence of various infectious diseases, in particular influenza, cholera, and enterovirus infections. This region is particularly vulnerable to infectious diseases because it is densely populated (6.68 million people in 1998), is in the crossroads between the East and the West, encounters a heavy volume of international travel, and has live poultry markets in close proximity to residential areas.

Influenza A Virus (H5N1)

In 1997, a total of 18 cases of human infection with influenza A virus sub-type H5N1, which was previously known to infect birds only, occurred in Hong Kong. The first case appeared in May 1997; the remaining cases occurred in November and December 1997. They involved 8 males and 10 females ages 1 to 60 years. Half of the cases occurred among children at or under age 12. All of the patients presented with a high temperature and a sore throat; the majority also developed a cough. Six individuals died as a result of viral pneumonia and multiorgan failure. Genetic sequencing confirmed the avian origins of the viruses isolated from patients. Results of an investigation indicated that the main mode of transmission was from bird to human. Human-to-human transmission was documented but was found to be relatively inefficient and uncommon. Epidemiological studies showed that the major risk factor was visiting poultry stalls in a market the week before the onset of illness.

In view of the evidence that the H5N1 virus affected chickens in the local community, a slaughtering exercise was launched on December 29, 1997; a total of 1.5 million poultry were killed. This measure effectively brought the outbreak to an end. A whole host of measures was introduced to ensure that the poultry sold in local markets were safe. They included quarantine and testing of imported chickens, segregation of chickens from ducks and geese, and improvement of hygienic conditions in the markets. Close attention to surveillance of humans and animals for evidence of influenza was maintained while preparation of pandemic plans and the development of vaccine and antiviral agents continued.

This outbreak illustrates the importance of a robust public health infrastructure for disease surveillance and the need for international efforts and multidisciplinary collaboration to address the threat of influenza. Apart from disease prevention and control, due consideration should also be given to the economic

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