There was a documented case of measles in San Mateo County last month, but we are only learning about it now as public health officials say they conducted contact tracing, and they determined there was no further risk.

As KRON4 reports, the San Mateo County Health Department has gone public about a case of measles that occurred in the county in February. Officials did not share any details about the patient who was sick, including their age, but only said that the infection was the result of "travel."

"In this case, our investigators were able to reach everyone considered a potential exposure, and there was no further risk," the health department said in a statement to KRON4.

The reason the case was not publicized earlier, they said, was that the department's policy is not to share information about an investigation like this unless there is an ongoing threat to public health.

Measles outbreaks have been occurring in recent months in Texas, Kansas, and elsewhere. The CDC has recorded 483 confirmed cases so far in 2025; comparatively, there were only 285 total confirmed cases in all of 2024 in the US. The largest portion of the cases, 373, have been reported in Texas, but cases have been recorded this year in over a dozen other states, including 43 cases in New Mexico, and 8 cases in California.

The majority of the cases, 75%, have occurred in children or teens age 19 or younger, and 97% occurred in individuals who were unvaccinated or had unknown vaccination status for measles.

CBS News published several maps of where cases are occurring, and where vaccination rates are highest among kindergartners. California is among the states where 95% or more of children are vaccinated, but percentages are lower in Texas, and lowest in places like Idaho, where 79.6% of kindergarten-age children were vaccinated in the last school year.

Top image: Boxes and vials of the Measles, Mumps, Rubella Virus Vaccine at a vaccine clinic put on by Lubbock Public Health Department on March 1, 2025 in Lubbock, Texas. Cases of Measles are on the rise in West Texas as over 150 confirmed case have been seen with one confirmed death.(Photo by Jan Sonnenmair/Getty Images)