TORONTO -- Saudi Arabia has discovered another infection with the novel coronavirus, the World Health Organization announced Thursday.

The infected person was hospitalized in late January and died on Feb. 10, but confirmation of the infection was only made Feb. 18, the WHO said in a statement. Further investigation of the new case is underway.

The Geneva-based agency urged countries to consider testing for the new virus when patients present for care with unexplained pneumonias or when patients with severe, progressive or complicated respiratory illnesses don't respond to treatment -- especially if those patients have recently travelled to or come from parts of the world where infections have occurred.

To date, cases have been linked to three countries in the Middle East -- Saudi Arabia, Qatar and Jordan.

The new case is the 13th confirmed infection and seventh death caused by the new coronavirus, which the WHO is calling NCoV.

In addition, there are nearly a dozen cases the WHO considers "probable" infections -- people who were exposed to cases and who later became sick but who were not tested or weren't tested in time. If an infected person had recovered from the illness, current tests -- which look for virus DNA in mucus -- would not find evidence of infection.

Some laboratories are working to develop a blood test that will detect antibodies to the virus. Once blood tests are available it should be possible to figure out whether some of the probable cases were actually infected.

One instance where such a tool would be useful involves the current cluster of NCoV cases in Britain.

A man who had recently travelled to Pakistan and Saudi Arabia became severely ill after his return. He tested positive for the virus, as did two other members of his family who had not travelled abroad. But a fourth infection may have also occurred in that family.

Health officials investigating how the virus moved from one member of the family to the next suspect another relative may have contracted the virus and may even have spread it to the third confirmed case in the cluster.

This fourth family member had a respiratory illness but was not tested until after she recovered, at which point the test came back negative, said Dr. Anthony Mounts, the WHO's point person for the outbreak.

Mounts said the U.K. cluster adds slightly to the agency's concern over the virus. But he said in the main British cases confirm some things the organization has already strongly suspected -- in some circumstances, person-to-person spread can occur. However so far, it appears those chains of infection has been short.

And while the first few cases were all severe, some infections produce only mild symptoms.

The third confirmed case in this cluster had mild symptoms and has since recovered. "The fact that she had such a mild illness really does raise our concerns about what we might be missing," Mounts admitted.

The WHO revised its new coronavirus case definition this week to remind doctors not to automatically rule out people with mild symptoms when they look for possible cases.

Mild infections are a mixed blessing. Obviously everyone would hope the virus didn't always cause severe disease. But people suffering only mild infections may be more likely to spread the virus -- if the virus transmits easily.

That's because people sick enough to be in hospital ICUs mainly encounter health-care workers protected by masks, but people with mild respiratory infections generally go about their daily life. And mild infections are much harder to spot, especially when they occur during cold and flu season.

Others share the WHO's concern about the possibility of missed cases. In fact, several of the researchers who were key players in the response to the 2002-2003 SARS epidemic admit the patterns they are seeing bring back memories.

"It is certainly beginning to look concerning, given the obvious fact that there can be onward transmission," said Malik Peiris, chair of the department of microbiology at the University of Hong Kong.

"It is somewhat reminiscent of the emergence of SARS in 2002."

Ron Fouchier, a virologist at Erasmus Medical Centre in Rotterdam, the Netherlands, also sees those similarities.

Fouchier is concerned about how many infections may be going unnoticed, untested or unreported. He noted that several of the 13 confirmed cases were diagnosed in European hospitals.

In addition to the current cluster in Britain, one case from Qatar was diagnosed in Britain in September and a second from Qatar was diagnosed in Germany in October. Both men got sick in Qatar but left the country for treatment -- a practice which is not uncommon for wealthy residents of Middle Eastern countries.

"The fact that we are finding these cases in Europe and not anywhere else, that has to raise suspicion," Fouchier says. "What we're seeing in Europe is just the tip of the iceberg and we really have no clue how big the iceberg is."

Saudi Arabia has now reported six cases. Qatar has had the two confirmed cases. And Jordan has reported two cases, but the confirmations came months after the two individuals died, after falling ill last April.

Mounts said the WHO is trying to get countries to look harder for the virus. "We're concerned and really watching it very closely and trying to push people to do more investigation."

He also said the organization is putting together networks of experts to help it with the coronavirus situation -- an approach the WHO used with much success during the SARS outbreak.

A laboratory network and a network of expert epidemiologists -- sometimes called disease detectives -- are being set up. As well, a group of clinical experts who have advised the WHO over the past decade on possible treatments for H5N1 -- bird flu -- and during the 2009 H1N1 pandemic is being reactivated to help with this situation, Mounts said.