A 76-year-old man was diagnosed Thursday with Middle East Respiratory Syndrome, according to the Korea Centers for Disease Control and Prevention.
The patient shared a hospital room with a man who was South Korea's first confirmed case of MERS, agency chief Yang Byung-Guk told reporters.
The first patient was not isolated initially because it wasn't known why he was ill.
Yang said the first patient had visited Saudi Arabia, Bahrain and the United Arab Emirates. His wife also contracted the disease.
All three are being treated in hospitals and they are not in critical condition, according to Yang's agency.
Additionally, 64 hospital workers and family members of the confirmed MERS patients have been quarantined, Yang said.
MERS was discovered in 2012 and has mostly been centred in Saudi Arabia. It belongs to the family of coronaviruses that includes the common cold and SARS, and can cause fever, breathing problems, pneumonia and kidney failure. The virus is thought to be primarily acquired through contact with camels, but it can also spread from human fluids and droplets. A number of cases in Saudi Arabia have involved health workers caring for MERS patients.
There have been a total of 1,142 cases of the virus worldwide and 465 have died, according to the European Center for Disease Prevention and Control. Of the fatalities, 428 have been in Saudi Arabia.