An unvaccinated traveler, infected with measles in the U.S. before international travel, initiated an outbreak in Colorado during May-June 2025. This individual, infectious upon arrival at Denver International Airport, led to nine secondary and one tertiary measles cases among Colorado residents, including four hospitalizations. Diagnostic methods included RT-PCR from nasopharyngeal swabs and urine, with urine testing proving crucial for vaccinated individuals who tested negative on NP swabs. Seven additional cases were reported by other jurisdictions. Vaccinated patients generally experienced milder symptoms. The outbreak underscores the critical role of vaccination and highlights the enhanced sensitivity of urine specimens for measles detection, especially in vaccinated persons.
Key note: Urine specimen collection significantly improves measles case identification, particularly in vaccinated individuals who may present with modified illness.