New York

Health officials were intensifying their efforts this week to control an international outbreak of mystery pneumonia.

Officials at the World Health Organization (WHO) are reporting a continuing rise in their tally of patients who have contracted the condition — dubbed severe acute respiratory syndrome (SARS). As of 24 March, 456 cases and 17 deaths had been reported in 13 countries.

But doctors have partially succeeded in restricting the spread of SARS by isolating patients and using measures such as face-masks to block exposure to coughed-up droplets bearing the pathogen.

A worldwide group of at least 11 collaborating laboratories is also making headway in identifying the microorganism behind the disease, and developing a simple diagnostic test.

On 24 March, researchers at the US Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, reported that the SARS pathogen might be a new member of the coronavirus family, which includes viruses that cause some common colds and respiratory infections. Particles found in the tissues of some SARS patients had a similar structure and genetic sequence to known coronaviruses.

This followed suggestions last week that the pathogen responsible might be a previously unknown member of the Paramyxoviridae family, which includes the agents that cause measles and mumps.

But those involved in the investigation warn that these candidate viruses may simply be coincidental infections. Wolfgang Preiser at the Institute for Medical Virology in Frankfurt, Germany, says that it would be “premature to claim victory” in identifying the virus.

Preiser's laboratory, among others, is now attempting to grow the pathogen and match its genetic sequence with known specimens. But to prove beyond doubt that a candidate virus is causing SARS, additional 'gold-standard' tests will be needed, says virologist Albert Osterhaus of Erasmus University in Rotterdam, the Netherlands.

One such test is the enzyme-linked immunosorbent assay (ELISA), which can detect antibodies produced by the patient's immune system to fight a particular virus.

The CDC announced that it has already had some success with similar techniques and that several recovering patients seem to have antibodies against the coronavirus that they have isolated.