The World Health Organization has issued a blunt assessment of the coronavirus outbreak in Saudi Arabia, acknowledging for the first time that there are concerns the virus may be spreading from person to person, at least in a limited way.

The statement called for urgent investigations to find the source of the virus and learn how it is infecting people. And it reminded countries they have a duty to the international community to rapidly report cases and related information to the WHO.

The worrying appraisal of the situation was echoed in a revised risk assessment issued Friday by the European Centre for Disease Control. It warned hospitals in Europe to be on the lookout for coronavirus cases coming in by air ambulance, saying the numbers of such patients may rise if the public in affected countries are afraid to seek care in their own hospitals.

The warnings come as health leaders from around the world are gathering in Geneva for the World Health Assembly, the annual general meeting of the WHO. The eight-day meeting begins Monday.

Though other nations have not publicly pressed leaders of coronavirus-affected countries for more transparency to date, it is likely that concerns about the virus and the opaque way investigations into it are being handled will be aired during the meeting.

"There is no formal agenda for novel coronavirus but I would be surprised if it didn't come up," WHO spokesman Gregory Hartl said in an interview.

Saudi Arabia, after all, is the home of Mecca. The holy site draws roughly three million Muslims from around the world every year to the Hajj, a mass pilgrimage Muslims are meant to perform at least once in their lifetimes. As well, nearly one million international tourists travel to Mecca during Ramadan -- the Muslim month of fasting -- to take part in another pilgrimage called Umrah.

Ramadan starts in the second week of July this year. And the 2013 Hajj will take place in mid-October, only five months from now. Experts watching the coronavirus situation are already worried about the potential for spread of the new virus, both within Saudi Arabia and internationally.

"I don't think anyone necessarily knows for certain what is or isn't happening," said Dr. Kamran Khan, an infectious diseases specialist at St. Michael's Hospital in Toronto. In his research, Khan tracks global travel patterns as a tool to predict and interpret spread of diseases.

"I'm not sure that there's an easy way to get at this information unless it's more forthcoming from within Saudi Arabia or any of the partners that are working with Saudi Arabia inside the country."

To date, the WHO has been notified of 41 confirmed infections with the virus, which has been recently named MERS, for Middle Eastern respiratory syndrome coronavirus. Of those cases, 20 have been fatal.

The bulk of the infections have occurred in Saudi Arabia, which is investigating a large and ongoing outbreak in the eastern part of the country, near the Persian Gulf. The most recent case -- an 81-year-old woman whose illness was announced Saturday -- is part of that outbreak.

In its statement, the WHO said two of the cases in that outbreak have no links to either other coronavirus patients or a hospital where some transmission is known to have occurred. These unconnected cases suggest two possibilities. They could have contracted the virus from its as-yet unidentified reservoir, which is thought to be one or more animal species. Or these cases could be a signal that undetected human transmission is happening there.

"The continued appearance of cases that are not part of larger clusters, and who do not have a history of animal contact, increases concerns about possible community transmission. This possibility is being investigated by authorities in Saudi Arabia," the WHO statement said.

Other countries that have reported cases are Jordan, Qatar, the United Arab Emirates, Germany, Britain and France. But the infections in the European countries all had their origins in the countries on the Arabian Peninsula.

The statements from the WHO and the ECDC both underscored how little the world has learned about the new virus since its existence was first revealed last September.

"It is unusual to have such a degree of uncertainty at this stage in an outbreak," the European health agency's statement noted. It called the information that has been shared about the cases, including the current Saudi outbreak, "insufficient."

The ECDC statement also said at this point it cannot exclude the possibility that the virus is acting in a SARS-like manner, especially given that transmission in hospitals have now occurred in Jordan, Britain, France and Saudi Arabia. The MERS virus is from the same family as the SARS coronavirus.

Hospitals played a key amplifying role during the 2003 SARS outbreak, with undetected cases infecting other patients, visitors and health-care workers. In fact, health-care workers made up about 21 per cent of the roughly 8,400 probable SARS cases.

The criticisms and concerns embedded in the two statements might appear mild but in the world of public health diplomacy, they are unusually frank.

One expert called the WHO statement a shot across the bow for the countries that have been the sources of MERS infections.

"When you see those words you realize that this is not being handled," said Michael Osterholm, director of the Centre for Infectious Diseases Research and Policy at the University of Minnesota.

"The WHO statement and the ECDC both -- they're really important statements."

But even at that, Osterholm fears the time for carefully worded warnings may be running out.

"You've got to kind of call the code," he said. "Either there is going to be an intensive effort made to understand what's going on in the Middle East and appropriate control measures brought to bear or potentially we're going to be asking a lot of questions one day as to why we didn't do more."

Neither the WHO nor the ECDC is currently calling for the type of travel advisory the WHO levied on Toronto during the SARS outbreak. At the height of SARS, the WHO urged world travellers to stay away from afflicted areas, including Toronto.

But the ECDC said European travellers to the Arabian Peninsula and surrounding countries should be informed of the infection risk. And companies that operate medical evacuations should be reminded of their responsibility to try to prevent transmission of infections across borders.

It suggested that mapping the medical evacuation routes from that region would help to identify which centres in Europe might be at greatest risk of receiving unidentified coronavirus cases.