Measles Outbreak Investigation at a University Dormitory in the Republic of Korea, 2024.

BACKGROUND: Five international students from Uzbekistan were diagnosed with measles in a university dormitory on April 15, 2024. This study was an epidemiological investigation to identify the transmission route of the measles outbreak in University A and to prevent further spread. METHODS: Measles cases were defined as individuals who tested positive for measles virus using real-time reverse transcription polymerase chain reaction. A retrospective cohort study was conducted on the dormitory residents. Relative risks and 95% confidence intervals were calculated to assess risk factors in the dormitory. Measles antibody testing was performed to assess immunity. Measles vaccinations and cohort isolation were implemented in the dormitory residents to control the outbreak. RESULTS: The primary case, also the index case, was a 19-year-old male student from Uzbekistan who resided on the second floor of the dormitory. All cases were reported among dormitory residents, with an attack rate of 5.3% (22/418). The student's mother in Uzbekistan had contracted measles. Risk factors for measles transmission included men, teenagers, students in the Global Business Department, students from Uzbekistan, and those who resided on the second and third floors of the dormitory. The seropositivity rate of anti-measles immunoglobulin G in Uzbek residents was 26.5%, which was lower than those in Vietnamese (36.8%) and Kyrgyzstani (41.7%) residents. No additional infections were reported after the last two cases on April 19. CONCLUSION: The measles outbreak in University A was likely to be caused by the index case from Uzbekistan. To reduce cases with imported measles, verifying the measles vaccination status of international students and administering preemptive vaccinations are needed.