Fear of modern-day pandemic has biologists scrambling desperately to contain new outbreaks of chilling disease
It is the ghosts of 1918 who make Hong Kong's bird flu outbreaks so chilling for disease experts today.
Twenty million people died suddenly that year when an unusual and particularly cruel influenza A virus broke out simultaneously across the world.
'Spanish flu' whipped around the world in four months, felling the young and strong as readily as it struck those normally at risk of infection. Its symptoms were not coughs and sneezes - victims' bodies were bloody and they drowned as fluid filled their lungs. They were often dead within a week.
It is the fear of another pandemic - but this time spread with the aid of passenger jets crossing the globe - that has biologists desperate to contain new outbreaks.
The source of the 1918 flu - identified as H1N1 - is still a mystery. The closest known flu strain is one found later in pigs, and some scientists believe it could have come originally from birds.
Influenza A viruses are volatile. They mutate quickly and what starts as a fairly mild disease can rapidly become something far more vicious.
The fear is that if a virus in animals can be transmitted to humans, it could further mutate to become as contagious to humans as the common cold, passed along with a sneeze.
Hong Kong's first bird flu outbreak started - and initially appeared to finish - in chickens. In March 1997, close to 7,000 birds on three New Territories farms were wiped out by an H5 strain. As a precaution, all the farms' other birds were slaughtered and the outbreak looked to have been contained.
Two months later, on May 21, a three-year-old boy died of respiratory complications. It was not until August that tests on his blood showed he had been infected with an H5 flu virus known to be lethal in birds and he became the world's first known human carrier.
How the boy contracted the disease is not certain, but some point to the fact that chicks and ducklings kept in a 'nature corner' in his kindergarten classroom had died before he fell ill.
While a handful of people the boy had been in contact with tested positive for antibodies, none had been ill and doctors breathed a little easier.
In November, however, a two-year-old boy tested positive for H5. He recovered, but the recurrence of the disease had specialists nervous.
Less than a month later, a man aged 54 died of apparent pneumonia. He, too, was found to be carrying H5. Within days, a 13-year-old girl was also diagnosed.
This was in early December and, by a week later, three more H5 cases had turned up, two of them in children. Another New Territories chicken farm then reported an H5 outbreak.
The Government ordered a mass slaughter of all poultry to contain the outbreak and, on December 28, more than a million birds were killed. That day, the infection rate among chickens in local markets was put at 10 per cent, with ducks and geese also found to be carriers. Altogether, the 1997 outbreak led to 18 confirmed H5N1 cases in humans. Six of those patients died.
Microbiologists said later that the poultry slaughter had drastically reduced the chances of more people coming into contact with H5, and there have been no human cases diagnosed since.
In February this year, H5N1 was detected in local poultry but did not kill the chickens it infected. Yesterday's announcement marked the first H5N1 deaths since 1997.
Local and overseas microbiologists were never convinced that H5N1 and the threat it posed to public health had died with the slaughtered chickens.
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