Unvaccinated Traveler Spreads Measles to 17 Individuals Across US

Researchers from the US Centers for Disease Control and Prevention (CDC) reported in The Journal of Infectious Diseases that an unvaccinated adult, infectious with measles, traveled from Europe to the United States last year and transmitted the virus to 17 individuals.

Investigation Details

The report, published last week, involved analysis of case samples, data from the CDC’s Port Health Activity Reporting System, and health department investigations. Researchers described contact-tracing efforts, environmental assessments, and laboratory testing. Flight records were reviewed to identify the locations of the index and secondary patients at the arrival airport.

In May 2025, the CDC was informed of an adult who traveled commercially from Europe to Denver International Airport, Colorado. This individual then stayed in a hotel overnight before taking another flight to North Dakota. During travel, the patient exhibited a fever, persistent cough, cold-like symptoms, and conjunctivitis. A rash developed one day after the domestic flight.

Transmission and Vaccination Status

Contact investigation identified 135 domestic travelers exposed to the index patient. Fifteen individuals (13 adults, two children) contracted the infection: five during international flights, three during domestic flights, and seven at the airport. The virus subsequently spread to two additional individuals outside their households, resulting in a total of 17 infections.

Among the 15 secondary patients, ten had documented or self-reported receipt of at least one measles vaccine dose, and five were unvaccinated. Five patients, comprising three unvaccinated individuals and two who self-reported vaccination, required hospitalization.

Regarding the two tertiary patients, one had confirmed receipt of two vaccine doses and was exposed to a secondary patient who self-reported vaccination. The other tertiary patient was unvaccinated and exposed to an unvaccinated secondary patient.

Recommendations

The study authors stated that vaccination is recommended for all travelers aged 6 months or older prior to international travel. They also suggested that travelers exhibiting fever or other signs of transmissible illness, such as coughing or malaise, should be encouraged to delay travel while symptomatic. A similar travel-related outbreak was reported by CDC and state researchers in late January.