Lessons from a Measles Outbreak in a Military School: Rapid Response and Surveillance Gaps in Sattahip District, Chonburi Province, Thailand, 2025

Objectives: To confirm a measles outbreak in a military school in Sattahip District, Chonburi Province, Thailand, describe its epidemiologic characteristics, identify associated risk factors, and assess surveillance performance and response timeliness. Methods: A descriptive and analytical field investigation was conducted among 374 cadets and staff from 30 Jun to 31 Aug 2025. Data were collected through case interviews, environmental assessments, record reviews, and laboratory testing. A retrospective cohort study was performed to identify risk factors. Hospital reporting performance was evaluated, and outbreak response timeliness was assessed using the WHO 7-1-7 detect–notify–respond framework. Results: Thirty-two measles cases were identified (attack rate 8.6%), all among male cadets. Two waves of transmission occurred, first among second-year cadets and later among first-year cadets. Laboratory testing confirmed measles virus genotype D8 (DSID 9587), genetically related to strains previously detected in the district. Sharing a bathroom with a symptomatic individual (adjusted odds ratio (AOR) 3.12; 95% confidence interval (CI) 1.17–8.33) and close contact with a measles case (AOR 2.31; 95% CI 1.02–5.22) were risk factors, while leaving the school premises was protective (AOR 0.34; 95% CI 0.15–0.74). Outbreak response immunization achieved 100% coverage among cadets and staff and likely interrupted transmission within two incubation periods. Facility-based surveillance evaluation showed low reporting sensitivity (1.04%), indicating underreporting of clinically compatible cases. Although the overall response met the 7-1-7 timeliness targets, delays in symptom reporting and operational constraints were observed. Public Health Recommendations: Strengthening measles surveillance sensitivity, improving early case reporting, and ensuring rapid outbreak response immunization are essential to prevent transmission in closed institutional settings.