A strain of bacteria was cited Tuesday as the cause for the mystery disease with pneumonia-like symptoms that struck Konkuk University in Seoul in October.
The Korea Centers for Disease Control and Prevention (KCDC) announced its months-long epidemiologic investigation into the disease which has affected 55 people since Oct. 19.
All patients were students working at laboratories in the school's College of Animal Bioscience and Technology building, and were discharged from hospital care later as their condition was not life-threatening.
The KCDC said the type of bacteria, saccharopolyspora rectivirgula, was discovered in multiple samples taken from the patients and the university labs.
"Based on the results of the lab examinations, we believe that the disease resulted from the bacteria that may have proliferated in the feedstuffs kept in the labs," said KCDC Director Yang Byung-guk during a media briefing.
Saccharopolyspora rectivirgula is commonly found in soil or in plants. Agriculture workers who come into frequent contact with hay are prone to inhale the bacteria, the KCDC said.
It said researchers at the college failed to store the feedstuffs properly in the labs and this may have contributed to the infection.
"The researchers kept the feedstuffs in their rooms where they sleep and eat," Yang said. "The infection may be attributable to long-term exposure under such conditions," KCDC Epidemic Investigation Team Chief Lee San-won said.
There had been no previous reports in Korea of human contraction of the bacteria.
"Currently known respiratory problems from the bacteria are allergic responses, but this case is infection, so it is different from commonly known cases," said Yang. "So we are presuming the disease was from the bacteria, not confirming that it is."
The KCDC is still investigating whether the bacteria was the sole cause or if other factors were involved. Up to three months are needed before the final results will be available, Yang said.
The bacteria traveled through air ducts, and the KCDC tests showed that the air from the fifth floor, where there are a lot of laboratories experimenting with feedstuffs, traveled through the ducts to the fourth and seventh floors.
Twenty-five people contracted the disease on the fifth floor, 15 on the fourth, 13 on the seventh, and one each on the sixth and the third. The 55 accounted for more than 20 percent of the total of 254 researchers in the building.
The KCDC said they plan to take necessary safety measures including sterilization of the building ahead of the spring semester next March. The university building in question has been shut down since the outbreak.