An unvaccinated adult who traveled to the United States from Europe with an infectious disease. measles Last year, he spread the virus to 17 other people, Centers for Disease Control and Prevention (CDC) researchers wrote. infectious disease journal.
In the report, released late last week, researchers analyzed case samples and data from the CDC’s Port Health Activity Reporting System and health department investigations to inform subsequent contact tracing efforts, environmental assessments, and laboratory testing. The team also examined flight records to determine the relative location of index and secondary cases at the arrival airport.
Index patient who traveled despite symptoms
In May 2025, CDC received a tip about an adult who arrived on a commercial flight from Europe to Denver International Airport in Colorado, stayed overnight in a hotel, and then boarded another flight to North Dakota. During the trip, the patient developed a fever, persistent cough, cold-like symptoms, and conjunctivitis (“burning eyes”), and developed a rash the day after boarding the domestic flight.
Travelers with a fever or obvious signs of a contagious illness, such as cough or fatigue, should be strongly advised to postpone traveling while they have symptoms.
Contact investigation identified 135 domestic travelers who came into contact with the index patient. Of these, 15 (13 adults and 2 children) were infected during international (5) and domestic (3) flights, and at the airport (7). The virus then spread to two people outside the household, making a total of 17 people infected.
Ten of the 15 patients with secondary infection had documented or self-reported receipt of at least one measles vaccination, and 5 had not been vaccinated. Five patients (3 unvaccinated, 2 self-reported vaccination) were hospitalized.
Of the two tertiary cases, one was confirmed to have received both doses of the vaccine and had contact with a secondary case who self-reported vaccination, while the other had not been vaccinated and had contact with a secondary case who had not been vaccinated.
“Vaccination is recommended for all travelers 6 months of age and older before international travel,” the study authors wrote. “Travelers with a fever or obvious signs of a contagious illness, such as cough or fatigue, should be strongly advised to postpone travel while they have symptoms.”
CDC and state researchers reported A similar travel-related outbreak occurred in late January.