With the diagnosis, the deceased is the sixth tertiary MERS infection case in the country, and the first death among them. He had been staying at the facility since May 9 for pneumonia, and shared a six-person hospital room with the 16th confirmed patient from May 28 to 30.

The number of MERS cases in South Korea therefore reached 36 as of Thursday evening. More than 1,600 -- an increase from 1,364 on Wednesday -- have been quarantined for possible infection. Over 600 people are considered as suspected patients.

Also on the same day, the Republic of Korea Air Force announced that one of its chief master sergeants has tested positive for MERS infection in an initial test at a military medical facility. The officer underwent another set of tests to finally be recognized as a MERS patient by the Health Ministry’s Center of Disease Control.

If confirmed, it would be the first MERS case in the Korean military.

Following the announcement, 91 soldiers and civilians working at the Osan Air Base in Pyeongtaek, Gyeonggi Province, were quarantined. The sergeant is currently asymptomatic, according to military authorities. The base is located near a United States Air Force base.

The officer had been hospitalized with a fracture at a civilian facility where the first confirmed MERS patient had stayed, before returning for duty.

Among the five newly confirmed patients, one of them has been identified as a health care professional at a large general hospital in southern Seoul. The 38-year-old treated the 14th patient on May 27, and began showing symptoms May 29. He was officially diagnosed on Thursday. Health authorities said the doctor hasn’t come in to work since May 29 and did not treat any patients since then.

As of Thursday, 28 out of 35 confirmed patients had all been infected at the same facility, which is the second of the four hospitals the first patient stayed at prior to his May 20 diagnosis. He stayed there from May 15 to 17. Up until Wednesday, the Health Ministry had been claiming that the first patient was the sole spreader of the disease in the facility, meaning all 28 of them were infected by the 68-year-old only, not by each other.

Yet Thursday, Kwon Jun-wook, a senior Health Ministry official leading an emergency task force team, said there is a possibility that tertiary infection cases may have already occurred at the facility from May 18 until May 29, the day the hospital was temporarily shut down. During this period, the first patient was not present in the facility.

“We acknowledge that what took place at this specific facility is very unusual,” Kwon told reporters. “We have been studying the cases that occurred in the facility very thoroughly and plan to take necessary action accordingly.”

Questions have been raised over the particular hospital’s sanitary conditions as well as sterilization practices. The hospital, which houses about 400 beds, opened in Pyeongtaek, Gyeonggi Province, in February. The building is reportedly less than a year old.

While the number of cases keeps growing, the Health Ministry is currently investigating if the virus has mutated in Korea and became more contagious. The investigation results are to be released on Friday at the earliest.

The average age of all 35 confirmed patients is 54, yet the largest number of them -- 34.5 percent -- are in their 40s. Among them, 17 were infected while being treated as inpatients at medical facilities, while 12 contracted the virus while either treating or visiting patients at hospitals. The disease has killed three people since the first case was confirmed on May 20. With the newly confirmed death on Thursday, the fatality rate rose 8.3 percent from the initial 5.7 percent. Currently, three patients have almost fully recovered.

As of Thursday afternoon, more than 900 schools and kindergartens have decided to cancel classes to prevent possible infection among school children.

Following the outbreak, the World Health Organization announced Korea could expect further cases of MERS, mainly because the first patient visited four facilities prior to his diagnosis and exposed a number of patients, hospital visitors and medical staff.

“The occurrence of such a large outbreak outside the Middle East is a new development, as is the exportation of the disease to a third country,” said the WHO in a statement Wednesday.

“Consistent application of adequate measures for infection prevention and control has halted other large clusters of cases associated with health care facilities. WHO recommends that droplet precautions be added to standard measures when providing care to patients with symptoms of acute respiratory infections.”

By Claire Lee (dyc@heraldcorp.com)