Margaret Chan, Health Director of Hong Kong, said today that the source of the current international outbreak of Severe Acute Respiratory Syndrome (SARS) seems to be a doctor from Guangzhou, the capital of Guangdong, the southernmost region of China, which saw 300 cases of a mystery pneumonia between November 2002 and February 2003. Chan's comments are reported in the Hong Kong Standard.

China only recently agreed to cooperate with the World Health Organisation (WHO) and the US Centers for Disease Control to share data and samples from that earlier outbreak.

The doctor stayed on February 21 with six other first ("index") cases of the current outbreak on the same floor of the Metropole Hotel in Mong Kok, Hong Kong. He died later in hospital.

The importance of this observation is to link the two outbreaks, so data can be pooled. For example China earlier claimed that the Guangdong disease had weakened after successive transmissions, although David Lowe, the Canadian doctor attending to the nine cases in Toronto — the first of whom, a 65-year-old woman, is believed to have stayed at the Metropole Hotel during the Chinese doctor's visit — told The Scientist that in his experience so far the disease had been equally severe in each successive case.

Julie Hall of WHO's Global Alert, Response and Operations Department — which is managing the WHO response to SARS — told The Scientist that the Chinese government had requested assistance in analysing its own data. "They have a mass of data from November through to February — epidemiological data and samples. The first wave of the investigation will be epidemiological, and WHO is helping China select experts who could help, and facilitating with the government in Beijing."

Meanwhile tentative identification in Germany and then Hong Kong of the causative agent as a member of the paramyxovirus family — viruses associated with other respiratory infections including the parainfluenza viruses and respiratory syncytial virus (RSV), as well as mumps and measles — is being treated with caution.

Hall warned "What [the German team] saw under the electron microscope were particles — not a whole virus, just fragments from one sample — of a paramyxovirus. The whole family look the same. It gives us a clue, but doesn't definitively diagnose it. We don't know which member of the family it is, and some of them are incredibly common, like RSV, which causes coughs and colds in children and is very prevalent. If it's a little bit of that it means absolutely nothing."

"But what the collaborating laboratories are doing now is PCR tests to check the DNA to try to identify which member of the family it may be, and antibody tests in patients against a whole range of paramyxoviruses. WHO is coordinating that," said Hall.

John Tam of the department of microbiology of The Chinese University of Hong Kong later confirmed detection of a paramyxovirus in local samples by electron microscopy, and subsequently with PCR, but it is still not clear if SARS can definitively be attributed to such a virus.

The Paramyxovirinae is a huge family also found in monkeys, cattle, pigs, dogs, mice, pigeons, and even seals, dolphins and rattlesnakes, and it is conceivable an animal form has "crossed over" into humans in South China and begun the present outbreak of SARS.