The fear of a swine-flu outbreak looms larger in Hong Kong now the city has confirmed its first infection. Like the rest of the world, we have been bracing for a global flu pandemic. On Wednesday, the World Health Organisation raised its pandemic alert level to five, one short of the maximum, signalling that the A(H1N1) flu virus was spreading more easily between humans.
Fears of a pandemic have come and gone since the H5N1 bird-flu virus began spreading across Asia in 2003, six years after first crossing the species barrier in Hong Kong to infect humans.
It was only 10 days ago that the WHO alerted the world to a new variant of swine flu suspected to have killed dozens of people in Mexico. Soon, cases of the same virus were confirmed in the United States.
Flu is an upper respiratory tract infection. Symptoms include fever, runny nose, sore throat, nausea, vomiting and diarrhoea. Flu viruses are found in many animal species. In humans and pigs, both H1 and H3 flu viruses have been found.
Flu is, by itself, rarely fatal. But it can lead to deadly complications such as pneumonia. A new strain comes up every now and then against which much of the population has no natural immunity, triggering a pandemic.
Swine flu is caused by a virus similar to the type of flu virus that, in various forms, infects people every year, but is typically found only in pigs or in people who have direct contact with pigs.
