The coronavirus (CoV) is related to the common cold. For months, scientists have believed it was behind severe acute respiratory syndrome, which has been responsible for 41 deaths in the Toronto area.

"The significance of the paper is confirming that this coronavirus does produce very serious disease," said Frank Plummer, scientific director at the National Microbiology lab in Winnipeg.

"Is it the whole explanation of SARS? I'm still not 100 per cent sure."

The researchers identified the virus by looking at clinical and post-mortem samples from 436 SARS patients in six countries.

They also injected the virus into four macaques (a type of monkey common in Southeast Asia), three of which went on to develop SARS-like symptoms.

"Collectively, these results of laboratory studies of SARS patients and experimental infections of macaques prove that the newly discovered SARS-CoV is the primary causal agent of SARS," said the study's lead author, virology Prof. Albert Osterhaus of Erasmus University, the Netherlands, in a release.

Frank Plummer

Plummer's team at the national microbiology centre was only able to find the coronavirus in 60 per cent of samples from SARS patients they looked at. He thinks there's something else going on that scientists don't yet understand.

One possibility is some people listed as probable cases actually had something else that looked like SARS.

Microbiologist Dr. Donald Low of Mount Sinai hospital in Toronto said it's vital to have a definitive diagnosis for SARS. "That's going to help us, especially if we see clusters of cases where we were able to get a number of different samples and if they come back negative being able to say this is not SARS."

Identifying the virus is an important step, but an effective treatment and vaccine for SARS are years away, according to scientists.

They say SARS could be a seasonal disease, poised to return later this year along with the usual cases of cold and influenza.

The coronavirus study appears in the July 22 online issue of the journal The Lancet.