SEOUL, May 28 -- The number of South Koreans infected with Middle East Respiratory Syndrome (MERS) rose to seven as two new cases were confirmed, and a suspected infectee left for China Tuesday for a business trip, the disease control center said Thursday.

The two cases included a 71-year-old man who had been hospitalized at the same ward with the patient zero and a 28-year- old female nurse who had treated the first patient, according to the Korea Centers for Disease Control and Prevention (CDC) under the Ministry of Health and Welfare.

The number of infectees increased to seven just eight days after the patient zero was confirmed positive on May 20.

The first patient was an unidentified 68-year-old male who traveled to the Middle Eastern region before returning to South Korea on May 4. His wife became the second patient who contracted the MERS corona-virus.

The third infectee was a 76-year-old man who shared a hospital room with the first patient, and his daughter who attended to the third patient became the fourth.

The doctor, who examined the patient zero earlier this month, became the fifth case infected with the deadly viral disease.

The MERS is a respiratory illness caused by a new type of corona-virus. The first case was found in Saudi Arabia in 2012. There is no vaccine or treatment for the disease, with its fatality rate reaching 40.7 percent.

A 44-year-old man, suspected of being infected with the MERS as he had close contacts with the third and fourth patients, left for China Tuesday for a business trip. He is the son of the third patient and the brother of the fourth infectee.

The South Korean health authorities notified the Chinese health authorities and the World Health Organization (WHO) of his departure to make the suspected infectee subject to examination and treatment.

Yang Byeong-kook, chief of the disease control center, told a press briefing that the South Korean man, who went to China, failed to notify the health authorities of his visit to his father during the initial epidemiological survey.

The man, who suffered a fever, saw a doctor Monday, and the doctor recommended he refrain from going for a business trip to China. But the man left for China Tuesday, neglecting the recommendation, Yang said.

The doctor failed to report the suspected case to the health authorities Monday, giving a belated notification on Wednesday, the CDC chief said.

To prevent contagion, the man's wife and the medical workers who contacted him were placed in self-isolation.

The health authorities are investigating into about 180 co- workers who closely or directly contacted the suspect.

The list of 28 passengers on board the same flight bound for China and seated near him was forwarded to the Chinese authorities. Aboard the flight were 80 South Koreans, 78 foreigners and eight flight attendants.

No case of tertiary infection, or contagion from the secondary infectee, has been found yet as all the six patients were directly infected from the patient zero, Yang added.