Scientists are trying to unravel a medical mystery involving a new type of coronavirus, which come from that same large family of viruses that bring us the common cold but also brought us Severe Acute Respiratory Syndrome - better known as SARS - back in 2002.

So far, two patients have been identified as having been infected with this new virus: A 49-year-old male from Qatar who was transferred to the United Kingdom for treatment September 11 and is currently in critical condition, and a 60-year-old Saudi Arabian man who was treated in June and has since died.

While the Qatari man is known to have traveled to Saudi Arabia, officials at the World Health Organization do not believe there's a connection between the two.

However, it has been determined that they both had the same symptoms, severe respiratory illness-like pneumonia and kidney failure. When samples from both patients were tested, researchers found they both were infected with the same virus.

This new virus was first identified and reported by Dr. Ali Mohamed Zaki at the Virology Laboratory of Dr. Soliman Fakeeh Hospital in Jeddah, Saudi Arabia. He had taken a sample from the Saudi patient's lungs before he succumbed to his illness. After comparing it to other cold and flu viruses and the SARS virus, it became clear that he had found a new virus, according a WHO spokesman.

Zaki then had his sample verified by a leading coronavirus researcher, Dr. Ron Fouchier at Erasmus University Medical Centre in Rotterdam, the Netherlands, according to his posting on the website for ProMed, the Program for Monitoring Emerging Diseases, on September 15.

Researchers in the UK also isolated the virus in the patient from Qatar and sent them to the Netherlands as well. Fouchier studied the genetic makeup of both and found them to be 99.5% identical.

On a molecular level, this new coronovirus more closely resembles the SARS virus which sickened 8,000 people and killed 774 between 2002 and 2003, than a cold virus.

But it doesn't seem to behave like SARS did, says WHO spokesman Gregory Hartl. These two men not only suffered from severe respiratory illness, they also had kidney failure, something that wasn't seen in SARS patients. Also, none of the close contacts or health personnel caring for the patients has become infected yet, says Hartl, but they are still being watched.

"There is reason to be interested and even concerned" about this new coronavirus, says Dr. William Schaffner, chairman of the Department of Preventive Medicine at Vanderbilt University Medical Center.

But he notes that when the SARS epidemic was going on, many of those caring for patients were infected too. The fact that this hasn't been seen with these cases so far is a good sign. "There's no evidence yet that these viruses are readily transmissible," says Schaffner, who is also the past president of the National Foundation for Infectious Diseases.

There are still many unknowns for researchers to uncover. Have there been other serious cases that haven't been reported yet?

"We don't know if this virus causes mild diseases also," says Hartl. "We don't know if this is two out of two cases or two out of 2 million (which might include a lot of mild cases)." The WHO has alerted physicians around the world to keep an eye out for more cases.

Doctors also don't know the source of the infection. A lot of disease detective work is required to further understand where these patients have been, may have eaten or any other behavior that might provide clues. In 2002, the source of the outbreak was linked to a ferret-like animal called a civet cat, but researchers now believe a horseshoe bat may have been the original source.

So far, no travel restrictions have been issued by the WHO. Those concerned about being infected can protect themselves by exercising proper hand-washing hygiene and cleaning surfaces that could harbor viruses.