Colorado Measles Outbreak Traced to Infectious Traveler on International Flight

A May–June 2025 measles outbreak in Colorado was linked to an infectious international traveler, resulting in nine secondary and one tertiary Colorado cases, with seven additional cases reported by other states. Notably, two vaccinated patients had the virus detected only in urine, highlighting urine RT-PCR as a potentially more sensitive diagnostic tool. Public health authorities identified about 1,400 contacts, offered postexposure prophylaxis, and emphasized full MMR vaccination (two doses) for travelers and staying up to date on vaccination.