Health authorities stepped up monitoring Thursday on students and faculty at Konkuk University in Seoul after an unconfirmed virus infected a total of 31 people and a school building was shut down.
Ten more were confirmed to be suffering from similar symptoms on the same day, after 21 had shown symptoms of high fever and coughing since last week.
The government said it is closely monitoring over 850 students and lecturers who have been using the College of Animal Bioscience and Technology building in northeastern Seoul, to check if more have been infected.
All the 31 patients are from three laboratories in the university building. Of the patients, 23 were placed in isolation at state-run facilities, while eight others were quarantined at home, with the government still trying to find the cause of the infection.
The university also put up posters around campus asking those who visited the bioscience building from Oct. 8-28 and who are showing suspicious symptoms to report to the Centres for Disease Control and Prevention.
SK Group, which used the building Sunday for a test for job applicants, said it would contact the candidates to notify them of the possible infection. The company refused to reveal the number of people who took the exam in the building.
Since a 26-year-old female student from the college showed symptoms on Oct. 19, 20 more students working toward their doctoral and master's degrees at laboratories in the building have contracted the unknown virus.
With the growing number of patients, Konkuk University shut down the whole building Wednesday, while the CDC conducted an epidemiologic inspection into the building and disinfected it earlier in the day.
"We assume that the source of infection is inside the building, but don't know what exactly it is," an official from the CDC said. "For now, there are no human-to-human infections and the virus hasn't spread outside the building."
As of Thursday evening, there were no additional cases of infection.
The first four graduate students showing symptoms allegedly visited a cattle fair in Gyeonggi Province as well as an animal farm owned by the university in Chungju, North Chungcheong Province, last week, triggering speculations that they might have caught the Brucellosis bacterial infection.
Brucellosis, which generally infects animals including cattle, sheep, goats and dogs, can be passed on to human beings when they come in contact with infected animals.
But professor Chang Won-joong, who is in charge of managing animals and plants for the university, dismissed the claims, saying the students had not touched cattle placenta. There is little possibility that their visit to the animal farm and cattle fair could be linked to the infection, he added.
Some experts suspect Q fever, which can be transmitted by air and is caused by the Coxiella burnetii bacteria found in the droppings of animals. Symptom such as fever, headache and muscle aches appear after a two-week incubation period.
The university is now waiting for the results of the inspection by the CDC.