A person infected with measles passed through San Francisco International Airport and two busy San Jose grocery stores, health officials have revealed.

The alert involves an adult from Santa Clara County who was infectious while passing through the major transport hub on Thursday morning between 8:30 a.m. and 11 a.m.

The individual moved through the international terminal, including passport control, customs and baggage claim areas.

Later that night, between 8 p.m. and 10 p.m., the same person visited two San Jose locations: Trader Joe’s and International Halal Market.

Anyone who was present at those sites during the specified time frames may have been exposed, officials said.

Because measles is among the most contagious diseases in the world, health authorities warned that symptoms could appear seven to 10 days after exposure and include fever, cough, runny nose, red eyes and rash.

Unvaccinated individuals are being urged to quarantine, avoid large gatherings and monitor for signs of illness for up to three weeks.

Officials also stressed that pregnant people, infants, immunocompromised individuals and the unvaccinated should seek medical guidance immediately if exposure is suspected.

Health officials warned that anyone developing symptoms should contact a medical provider before visiting in person, in order to reduce the risk of further transmission.

The situation comes as California records its highest annual measles count in seven years.

As of June 8, the state has confirmed 49 cases, already nearly double the total recorded in all of 2025 and the highest since 2019, when 73 cases were reported.

State data shows 94% of cases involve unvaccinated individuals, and more than 80% are in people under 19, highlighting ongoing gaps in immunity despite generally high vaccination coverage in the Bay Area.

Dr. Sarah Rudman, Santa Clara County’s health officer, emphasized that vaccination remains the strongest protection against measles and helps prevent widespread outbreaks even when exposures occur.

County officials are coordinating with the California Department of Public Health and the US Centers for Disease Control and Prevention on contact tracing tied to the exposure sites.