Limited details have been divulged. But the information that is available raises the spectre of person-to-person spread, potentially over several generations.
Some details of the new cases were provided Sunday by Dr. Ziad Memish, the country's deputy health minister. Memish submitted the information to ProMED-Mail, an Internet-based infectious disease tracking system.
"So far there is no apparent community transmission and transmission seem linked to one HCF (health-care facility)," Memish said in a short posting that revealed that two of the three new cases are already dead and one is on a breathing machine in critical condition.
Experts watching the outbreak with concern were quick to parse Memish's statement.
"While it's not explicitly stated that it's person-to-person (spread), with no evidence of an animal reservoir in the hospital the only conclusion that can be drawn is that this is person-to-person," said infectious diseases expert Michael Osterholm.
And given the number of cases and the range of dates of illness onsets, "we cannot rule out multiple generations of spread," he said.
The new cases bring the cluster to 13 infections, with seven deaths. Globally there have been 30 infections with the new virus, 18 of them fatal.
The first known case in the Saudi health-care cluster got sick on April 14. The most recent person to become ill started to have symptoms on May 1.
The incubation period of the disease — the time it takes for an exposed person to develop symptoms — is not completely clear. But there is certainly enough time between these cases for several generations of spread to have taken place.
"This is far too wide to be an incubation period," Osterholm said. "This (event) is much more complicated than that."
The three cases reported Sunday were a woman, 62, and a man, 71, both listed as having "multiple comorbidities" (pre-existing illnesses) and a woman, 58, with comorbidities. All of the other cases in this cluster have been described in that manner, which probably explains how they came in contact with each other.
Experts who have been following this virus — a member of the same family as the SARS virus — have been watching for hospital outbreaks. That's because spread within hospitals was a key feature of the SARS outbreak. Many of the people who caught the infection were health-care workers or hospital patients.
"All of us are painfully reminded that the early acceleration of the 2003 SARS epidemic occurred around the hospital-related transmission of the virus," Osterholm said.
"We can only hope that this is not deja vu all over again."
The outbreak occurred in Alhasa, which is also sometimes written as Al-Asha in English.
Memish's latest ProMED posting did not reveal anything about possible linkages between the cases. Two of the earlier patients in this cluster were related.
The start of this outbreak was first reported to the World Health Organization late last Wednesday. At that time, there were seven cases, five of whom had already died. On Friday, Saudi authorities informed the WHO that three more cases had been confirmed.
Authorities will now be looking to see if the virus is continuing to spread in this facility and whether people who work in the hospital contract it and take it out to their families and contacts.
In other words, will transmission of the virus continue, will the hospital be able to contain its spread or will the virus stop spreading if it encounters healthy people who may not be as vulnerable as these patients have been?
Since the first known cases of this infection occurred, Jordan, Qatar, the United Arab Emirates, Britain and Saudi Arabia have reported infections.
Britain reported the first confirmed cases of limited person-to-person spread, in a family where three members fell ill and two died. But the first case in that cluster seems to have contracted the virus while travelling in Saudi Arabia.
Saudi Arabia has amassed the most cases, 22 — and 13 of them have been fatal.
Saudi officials had been seemingly reluctant to provide details about the cases up until this cluster, but they are now providing at least some information through ProMED. However, details about the type of health-care facility this is and the scope of the problem are still missing.
And it is still not known where the virus comes from or how people are becoming infected with it. The virus's genetic sequence suggests it originated in bats. But it's not clear if an intermediary species of animals is infected and acting as a bridge to people.
The first known cases of the new infection occurred in April 2012, in a cluster of 11 illnesses in a hospital in Jordan. At the time, a reason for the outbreak wasn't found.
But months later stored samples from two of those cases — both died — were tested and found to be positive for the new virus. The other nine people survived and are suspected to have been infected. But it's not clear at this point if they will ever be confirmed.
The coronavirus was first spotted when a Saudi man died of a severe pneumonia last June. When the cause of his illness could not be detected, an infectious diseases specialist sent a sample to Erasmus Medical Centre in Rotterdam, the Netherlands, where virologists determined a new coronavirus was behind the infection.