Should we fear the killer flu?

IF you're on a train or a bus in Hong Kong, and you feel a sneeze or a cough coming on, you'd be advised to try and hold it in, at least until you get somewhere private. Such is the level of paranoia in this most densely-populated of urban sprawls, even the slightest sniffle is enough to earn a round of hostile glares.

Masks seem to be the must-have accessory of the moment; detergents and bleach are in everyone's shopping bag; children are being kept home from school. Panic is gripping the population.

And the reason is Severe Acute Respiratory Syndrome (SARS) - a new flu-like illness which has emerged in the Far East. First identified in China at the end of last year, it has so far infected more than 1,500 people, and claimed 54 lives. Among the victims was Dr Carlo Urbani, the World Health Organisation (WHO) specialist who was the first to identify the disease.

Initially confined to the Far East, moving from China to Hong Kong, Vietnam and Singapore, it has now spread to Canada, Germany and Australia. Three suspected cases have been identified in Britain. The US, Canada, Australia and Ireland have all advised travellers to avoid the Far East, and four airlines have cancelled or reduced flights.

Public health officials in the UK are advising that there is no reason to be concerned, but even though experts admit they know little about this new threat, there are some questions which can be answered:

Q. What is SARS?

A. SARS is a flu-like collection of symptoms, which is so new it is as yet poorly defined, according to Dr David Walker, director of public health for the County Durham and Tees Valley Strategic Health Authority. "It is clearly an infection, and it is almost certainly a virus infection, but, as yet we don't know exactly what it is," he says.

The two main candidates are a corona virus, similar to those which cause the common cold, and a paramyxovirus, similar to measles or mumps.

Q. Where did it come from?

A. The first recorded cases were in the Guangdong province of China, although the Chinese authorities suppressed the information for three months for fear of causing panic. It is thought to have been an animal virus, which underwent a genetic mutation, making it more dangerous to humans.

"It is quite common for these viruses to emerge - about 30 major infectious diseases have appeared over the last 25 years, including HIV and Legionnaire's Disease," says Dr Walker.

Q. What are the symptoms?

A. SARS usually begins with a sudden fever, a temperature of more than 100.4F or 38C, followed by coughing, shortness of breath or difficulty breathing.

Q. How is it spread?

A. The main method of transmission seems to be through a victim sneezing or coughing, sending droplets into the air which are then breathed in by someone else. Initially, it was thought it could only be spread through close contact, but some cases cannot be explained by this method, leading scientists to believe that it may be more contagious than they first thought.

Many early cases were among health workers caring for victims, but more than a third of the 600 cases in Hong Kong were in people living in one apartment complex in Kowloon, suggesting it could be transmitted through the air.

The incubation period is from two to seven days, although in some cases it could be as long as ten days. It is not known how long before symptoms appear that SARS could be transmitted to others, or how long a victim could be infectious for after they have recovered.

Q. How is it treated?

A. Antibiotics and anti-viral drugs are being used to treat SARS, but it is unclear if these are having any effect. Without knowing the cause, there is no specific treatment. No vaccine is available.

Q. How can I protect myself?

A. Only a handful of cases have been identified outside South-East Asia, and the majority of these have involved people who had visited the region. The Public Health Laboratory Service is recommending that people intending to travel to Hong Kong, Singapore, Thailand, Vietnam and China should be aware of the outbreaks, and report any symptoms, but is not advising people to avoid the region.

Hong Kong is asking all visitors to fill out a health declaration form, and the WHO is advising port authorities to screen travellers before departure.

Q. So, should I be worried?

A. The available evidence suggests that SARS is not highly infectious, nor is there a high mortality rate. Around three to four per cent of people with the virus die from it, the rest recover, usually within about seven days.

"When you have a very infectious disease, you have an explosion of cases, and that hasn't happened," says Dr Walker. "There are two kinds of illness that are frightening: the incredibly infectious or the incredibly virulent. This is not as infectious as flu, and it isn't as virulent as something like the ebola virus, which has a mortality rate of about 90 per cent in the early stages. It is unusual in that it is a new disease, but it doesn't look like an explosive pandemic."

But while SARS may not be a reason to panic, experts suggest that it could be here to stay. Unless there is wholesale slaughter of animals carrying the virus, there is likely to be a reservoir of infection, making SARS a permanent feature of respiratory disease.

When a deadly virus strikes

WHILE it may be causing concern in the Far East, Severe Acute Respiratory Syndrome (SARS) is seen as unlikely to repeat the devastation of previous pandemics.

The first known flu pandemic was in 1580, and has been followed by another 31, with flu drawing its devastating power from its ability to mutate easily and quickly.

The worst pandemic in history was the Spanish flu of 1918-1919, which killed an estimated 40 million people around the world, more than the combined totals of the two world wars.

The outbreak, also known as the Great Influenza Epidemic, preyed on mainly young, healthy adults, with victims being struck by bronchitis or pneumonia, death usually coming within 36 hours. Almost every country in the world was affected by a virus that probably killed more people in a shorter period than any infectious disease known to man.

There were two other pandemics in the last century: of Asian flu in 1957 and Hong Kong flu in 1968. In 1957, an estimated 30,000 people died in the UK, with GPs reporting up to 100 new cases a day. In 1968 there were 78,000 deaths in the UK. Around a million people died worldwide in each outbreak.

In 1997, health authorities in Hong Kong reported that, for the first time, a form of chicken flu had crossed over to humans, affecting 18 people and killing six. It was only stopped in its tracks when every chicken in the province was slaughtered.

Health experts say that pandemics tend to appear at regular intervals, with a best estimate of one every 30 years or so. It is now 35 years since the last one.