The organization says investigation of that cluster suggests that in some cases, infection with the new virus can be milder than what was seen in the first cases that came to the world's attention this fall.
The first observed cases involved people who become severely ill from infection with the new coronavirus, which is a member of the same family as the virus that caused SARS.
Of the nine people who have had confirmed infections to date, all were severely ill and five died.
The WHO says it now considers other patients from the Jordanian cluster to be probable cases.
But it says that based on what is known to date, it doesn't appear that at present the new virus can transmit to people easily or spread among them in a sustained manner.
In a statement issued Friday, the global health agency did not indicate how many people it considers as probable cases from the Jordanian outbreak, which centred on a hospital in Zarqa.
In April, before the existence of the new coronavirus was recognized, the Jordan Times reported that there was an outbreak of an unknown illness causing pneumonias at Zarqa Public Hospital.
The newspaper cited Abdul Latif Wreikat, Jordan's minister of health, as saying there were 11 cases. Seven were nurses, one was a doctor and one was a brother of one of the nurses. The article did not indicate who the other two patients were.
Two people in this cluster of cases died of their infections. Once the existence of the new coronavirus became known, stored samples taken from the two patients who died were tested for the virus and they were confirmed as cases.
In November, the WHO sent a team to Jordan to investigate the outbreak at the request of the Jordanian government. The team went over case records and interviewed surviving patients, their relatives and caregivers.
The team was unable to determine which was the first case in the cluster. Knowing who got sick first might help investigators home in on how the virus is moving from its natural reservoir — suspected to be bats — to people.
Most family members and the health-care workers who looked after the cases did not become ill, the WHO says.
"However, the appearance of pneumonia in some who provided care and in at least two family members with direct personal contact increases the suspicion that person-to-person transmission may have occurred," the agency says, though it added it cannot rule out the possibility that all the patients were infected from a common environmental source.
The Jordanian cluster is not the only time person-to-person spread of the virus is suspected to have occurred. In November, Saudi Arabia reported that three members of the same family had tested positive for the virus.
A fourth family member was sick at the same time. And while he tested negative, the WHO considers him a probable case. (Tests that look for fragments of virus in a patient — the type used on this man — can miss infections depending on when in the course of an illness they are done.)
Saudi Arabia and Qatar are the only two other countries to have reported cases of this infection.
The report of the Jordanian investigation reveals that none of the cases had travelled outside of Jordan in the time preceding the outbreak. And none of the confirmed or probable cases had contact with animals.
The WHO says all the patients had pneumonia. But the disease was generally milder in the unconfirmed probable cases. It notes that one of the probable cases did not need to be admitted to hospital; his or her symptoms were mild enough that home care was sufficient.
It notes that the patients in the Jordanian outbreak did not suffer from kidney failure, which had been seen in several of the Saudi and Qatari cases.
The WHO says that when a blood test becomes available, testing of the probable cases may lead to additional confirmations and may help investigators figure out the types of exposures that led to infection — in other words, why some people got sick and others did not.
The WHO continues to urge countries to be on the lookout for the new coronavirus, and says hospitals should consider testing patients with unexplained pneumonias for the new virus, especially if they are residents of, or returning from, the Arabian peninsula and neighbouring countries.Suggest a correction