Authorities in Saudi Arabia have found two more people who were infected with the new coronavirus in a large cluster of cases in the eastern portion of the country.

The two new cases, reported Thursday, bring the total to date of that al Hofuf cluster to 15 infections. Seven have been fatal.

One of the newly reported cases became ill on April 6, which at this point is the earliest onset date known for any of the infections in this cluster. Though it is still not clear if these cases are all part of a chain of person-to-person spread, it does suggest the new virus has been infecting people in al Hofuf for more than a month.

The new cases were reported publicly by the country's deputy health minister, Dr. Ziad Memish, who posted a short update on the outbreak on the Internet-based disease surveillance system, ProMED.

Memish said the two people were not newly infected but rather cases that were detected by going back through records and tracing people who had been in contact with known cases. But his ProMED report did not say if these people are related to, or had contact with, any of the other cases in the cluster.

And while the official Saudi line has been that all the cases have been linked to a dialysis clinic at al-Moosa Hospital, Memish's post made no mention of these cases having had care at that facility.

He did, however, appear to suggest that there is no ongoing spread of the virus at this time, noting that it has been more than a week since the most recent case fell ill.

"Actions implemented and fully applied by 1 May 2013 have been effective to date in preventing new cases related to this cluster from emerging," Memish wrote in his ProMED posting.

But infectious diseases expert Michael Osterholm said it is too soon to conclude transmission in al Hofuf has been stopped.

"This cluster could still be continuing. I don't think we know," said Osterholm, who is the director of the Center for Infectious Diseases Research and Policy at the University of Minnesota.

"It would not surprise me in the next seven to 10 days if we find more cases have occurred in that area that have not previously been reported," he said, adding the ongoing investigation there may uncover more retrospective cases.

"I think the more of the onion we peel back here, the more difficult it gets."

The new cases are both men and are both alive. Both men were reported to have had pre-existing medical conditions.

One, a 48-year old, started to have symptoms on April 29. He is in stable condition in hospital. The other is a 58-year-old man who had symptom onset on April 6. Memish said he has recovered completely and was discharged from hospital on May 3.

The al Hofuf cluster is the largest to date with the new coronavirus and it is linked to one or more health-care facilities. That feature of the outbreak raises red flags for infectious disease experts because health-care workers and hospital patients are often the sentinel cases when a new pathogen begins to spread.

Such was the case during the SARS outbreak in 2003. The SARS virus spread poorly in the community but took off in hospitals among unprotected health-care workers and patients. This virus is from the same family as the SARS coronavirus.

Over the past 13 months, 33 new coronavirus cases have been confirmed in Saudi Arabia, Qatar, Jordan, the United Arab Emirates, Britain and, earlier this week, France. All cases are linked to the countries on the Arabian Peninsula. Eighteen of the cases have been fatal.

Saudi Arabia has reported the most cases, 25, with 14 fatalities.

The kingdom's officials have been reluctant to share information about the outbreak but recently invited some outside experts to travel to Saudi Arabia to consult on the situation.

Toronto SARS expert Dr. Allison McGeer is among them. The head of infection control at Toronto's Mount Sinai Hospital, she is currently in Saudi Arabia helping with the investigation.