The disease, known as MERS, is known to have infected 145 people in South Korea since the first patient was identified on May 20. The outbreak is the largest to date outside the Middle East, where the virus first emerged in 2012 in Saudi Arabia and has killed more than 400 people.

One of the tasks of the joint mission was to determine why so many people were infected in South Korea in a relatively short period of time. On Saturday, Keiji Fukuda, chief World Health Organization official on the panel, pointed to several factors: South Korean doctors’ unfamiliarity with MERS; the country’s “overcrowded” emergency rooms; the practice of “doctor shopping” for care at many different clinics; and the fact that hospital rooms here tend to be bustling with visitors. Nearly all of the country’s confirmed MERS patients were infected while seeking care or while visiting patients at hospitals. Hospital staff members were also infected.

Mr. Fukuda said the panel had found no evidence to indicate that MERS was spreading in the broader population. “However, continued monitoring for this possibility is critical throughout the entire outbreak,” he said. “Now, because the outbreak has been large and is complex, more cases should be anticipated.”

Both Mr. Fukuda and Mr. Lee said that the rate of new infections was decreasing, as South Korean officials have improved their communications with the public and carried out stronger infection-control measures. Twelve new MERS cases were reported Saturday, and seven more on Sunday.

The government has come under heavy criticism for withholding critical information early in the outbreak, like the names and locations of hospitals where infections had occurred. It eventually released the hospitals’ names, weeks after the first case was discovered. The outbreak has been a blow to President Park Geun-hye, whose approval rating has fallen in recent weeks.