Hallym University Sacred Heart Hospital, a tertiary medical institution in Anyang, Gyeonggi Province, reported a measles outbreak to the health authorities and the local government.

Most of the patients are employees of the hospital, but the hospital has yet to find the origin of the infection during the past eight days.

The provincial administration said that 25 patients, including 21 workers of the hospital, were confirmed with measles infection, and health officials were checking more than 4,300 people who contacted the patients. Measles spread from person to person through direct contact with discharge from the nose or throat.

Out of the 25 patients, 14 were ordered to stay at home, one was hospitalized, and 10 were released from quarantine.

The 21 hospital employees include four physicians, 14 nurses, one pharmacist, one medical technician, one employee, one caregiver, and one medical student.

The health authorities are actively monitoring 1,734 out of the 4,349 people who contacted the 25 patients, calling them twice a day to check they have any symptoms. The officials also noted the rest 2,615 people, who were more distant to the patients, to report any symptom.

According to the Korea Centers for Disease Control and Prevention (KCDC), the Sacred Heart Hospital conducted antibody tests on over 1,800 workers immediately after learning the outbreak of measles and found a confirmed case.

A KCDC official said the Gyeonggi Province was conducting an epidemiological study on the hospital.

“Three epidemiological investigators are carrying out the study. They are the ones who did a similar study when measles broke in Ansan, Gyeonggi Province, in January,” he said.

The KCDC was putting priority in checking people who had contact with the patients because some of them could be confirmed with measles from this week. “Health officials from Gyeonggi Province are doing the best they can,” he added.

In Daejeon on Sunday, a pediatric specialty hospital reported five cases of measles.

The first confirmed patient was a seven-month-old girl who had visited Vietnam with her Vietnamese mother. Travelers are advised to get measles vaccinations before entering Vietnam.

The four other children, who were confirmed with measles after being hospitalized in the same room with the baby girl, were aged from nine months to three years old. Except for the three-year-old child, the three were not old enough to get the first vaccination for measles.