World on alert as unidentified pneumonia strikes

International health authorities have gone on high alert as more reports emerge from south-east Asian countries of deaths and illness caused by an unidentified, potentially lethal pneumonia-like infection dubbed Hong Kong severe acute respiratory syndrome (SARS).

The director-general of the World Health Organisation (WHO), Gro Harlem Brundtland, said, "This syndrome, SARs, is now a worldwide health threat."

According to a Reuters report, the illness begins with 'flu-like symptoms, such as coughing, high fever and shortness of breath, and patients can deteriorate rapidly into pneumonia, with severe respiratory distress requiring mechanical ventilation.

On Friday, the Centres for Disease Control (CDC) in Atlanta, Georgia, activated its emergency operations centre after learning that two members of a Canadian family died of a severe, pneumonia-like infection after flying back from south-east Asia. Several other family members have developed similar symptoms.

The director of the CDC, Dr Julie Gerberding, told a media conference on Saturday that more than 150 cases had now been reported from a growing list of countries including China, Hong Kong, Indonesia, Philippines, Singapore, Thailand, Vietnam and Canada.

The CDC also issued a health alert to US hospitals and clinicians on Saturday, and began checking reports of illness among passengers passing through the US after potential exposure to the infectious agent in south-east Asia.

It is not yet known whether the agent of SARS is a virus or a bacterium.

No cases of SARS have been reported in Australia, but the Commonwealth Health Department, in a weekend telephone hookup with state public health officers, established a national reporting network to detect potential cases.

The department warned anyone who had been to Asia over the past two weeks, and who has developed a ‘flu-like respiratory illness, to contact their doctor.

Chinese outbreak

Last month the Chinese government reported an outbreak involving 305 cases of atypical pneumonia, including five deaths. It attributed the outbreak to a strain of the bacterium Chlamydia pneumoniae.

CDC has been working with the World Health Organisation (WHO) since late last month to investigate reports of atypical pneumonia outbreaks in Vietnam, Hong Kong, and in adjacent mainland China's Guandong province.

CDC and WHO experts have been monitoring the region for further outbreaks of an emergent strain of an influenza virus appeared in Hong Kong in 1997; of 15 people diagnosed with the new 'bird 'flu' since 1997, six have died.

Avian influenza -- so-called because it originated in infected chickens and ducks -- also causes a severe and potentially deadly infection. To curb a potential epidemic, Hong Kong health authorities ordered the immediate slaughter of every chicken on the island.

The 'bird 'flu' strain was designated the H5N1 serotype. The influenza virus generates major new serotypes by combining variants of about 15 hemagglutinin (H) and nine neuraminase (N) proteins found in bird-infecting strains.

Dangerous new forms of human influenza have been emerging episodically from south-east Asia for thousands of years. They are thought to originate in pigs, which are susceptible to both human- and bird-infecting 'flu viruses.

Pigs and poultry -- chickens and ducks -- are traditionally farmed together in Asia, and the 'mixing vessel hypothesis' proposes that recombinant strains originating in pigs caused the three great influenza pandemics of the 20th century.

The Spanish 'flu (1918) was an H1N1 serotype, the Asian 'Flu (1958) was an H2N2 serotype, while the Hong Kong 'Flu (1969) involved a H3N2 serotype.

Antibody tests have so far detected no direct human-to-human transmission of the H5N1 serotype. It appears to move directly from birds to humans, because the human isolates are essentially identical to those originating in chickens and ducks. There is no evidence of recombination between human- and bird-infecting strains.

In 1998, health authorities in Honk Kong diagnosed a new form of bird 'flu in two young, unrelated girls. It is a new hemagglutinin variant, serotype H9N2, which causes a relatively mild infection, and like the H5N1 serotype, does not appear to be transmissible between humans.

Epidemic overdue

A decade ago the Nobel laureate virologist Prof Joshua Lederberg warned that the next global influenza pandemic is overdue.

With modern jet travel, a new pandemic strain could reach to the six inhabited continents within 24 hours. The epidemic would burn through the world's densely populated cities even more rapidly than the deadly Spanish 'flu of 1918. The world population in 1918 was only 1.5 billion; today it is 6.2 billion.

The vigilance of the CDC and WHO reflects Lederberg's concerns.

While there is no evidence yet that SARS pneumonia is caused by a virus, there is a chilling prospect that one of the new Hong Kong viruses, or another new serotype, could mutate or recombine with a 'human' 'flu strain and spawning a lethal new virus capable of direct human-to-human transmission.

It can take up to six months to develop and mass-produce a new strain-specific vaccine; the Spanish 'flu of 1918, a haemorrhagic strain, killed healthy young adults within half a day of them developing the first symptoms of infection.

According to the CDC, early reports that infected patients did not respond to antiviral or antibody therapy appear to be incorrect - they probably reflect the scarcity of such drugs in many areas of south-east Asia.

The CDC's Gerberding told Saturday's telemedia conference, "We assume that this is spread person-to-person because we're seeing a large proportion of the cases in Asia among healthcare workers who were caring for the ill patients or household contacts of ill patients.

"We are recommending precautions to prevent airborne spreads, droplet spread and direct contact spread until we have further information. And so that means we're erring on the side of caution until we can be more specific."

Gerberding told a journalist the incubation period for the infection appeared to be between two and seven days. She said it was likely only the most severely infected patients have been diagnosed to date -- raising the possibility that the total number infected could be much higher.

Gerberding said that despite the recent diagnosis of two new cases of H5N1 avian influenza in Hong Kong, none of the SARS patients diagnosed so far had tested positive for H5N1 or any other influenza virus.

However, antibody tests only exist for known strains; SARS could conceivably involve yet another new variant of avian influenza.

Gerberding said there was no indication that the outbreak was the result of bioterrorism, because most of those infected so far were healthcare workers taking care of sick people, or family members or household contacts of infected individuals.

She said transmission patterns suggested the agent was not highly infectious: "It's very close personal contact of the type defined by WHO as having cared for, having lived with, or having had direct contact with respiratory secretions and body fluids of a person with the diagnosis.

"So there is no evidence to suggest that this can be spread through breath contact or through assemblages of large people; it really seems to require a fairly direct and sustained contact with a symptomatic individual."

According to a Reuters report, the SARS outbreak has alarmed travellers -- many passengers arriving in Hong Kong airport from Taiwan, Singapore and other countries at the weekend wore surgical masks.