California public health officials are issuing a warning about a potential measles exposure that may have affected multiple counties. The incident involves an unvaccinated individual who traveled through the state using Amtrak trains and regional buses. The traveler arrived in Los Angeles on an Amtrak train on September 10 and continued through several cities, including Bakersfield, Stockton, Oroville, Sacramento, and Emeryville, before departing for Denver. Anyone who was on the same trains or buses, or who visited the stations along the route during the relevant dates, may have been exposed to the virus. Health officials are working with federal and local agencies to identify and notify potentially exposed individuals. The traveler is reported to have passed through at least six counties: Alameda, Butte, Kern, Los Angeles, Sacramento, and San Joaquin, with multiple transfers along the way. Meanwhile, Pennsylvania is experiencing the most severe active measles outbreak in the United States. As of now, the state has confirmed 731 cases across 38 counties this year, with at least four deaths linked to measles-related illnesses. Officials in Pennsylvania have requested emergency assistance from the Centers for Disease Control and Prevention (CDC) to help manage the outbreak. However, the request may be withdrawn unless the CDC publicly acknowledges the four deaths. This comes after U.S. Health Secretary Robert F. Kennedy Jr. instructed the CDC not to recognize such fatalities. Kennedy recently addressed a conference hosted by the anti-vaccine group Children’s Health Defense, where he promoted unfounded concerns about vaccines while downplaying the urgency of measles vaccination. This latest California warning follows a similar incident involving Amtrak earlier this week. A person infected with measles traveled on a train from Sedalia, Missouri, to Chicago, Illinois, exposing over 250 people in Jackson County alone. The situation highlights the ongoing challenges in containing measles outbreaks, especially in the context of public transportation networks. Additionally, recent reports indicate that the Trump administration has changed the way measles deaths are counted during outbreaks. The CDC is now using data from the National Center for Health Statistics, which focuses on long-term mortality trends. The reason for this shift remains unclear, and it has raised questions about the transparency and consistency of public health reporting. Measles is a highly contagious viral disease that can lead to serious complications, especially in unvaccinated individuals. Vaccination is the most effective way to prevent the spread of the disease. Public health officials continue to urge people to stay up to date with their immunizations, particularly in light of recent outbreaks and the potential for widespread exposure through travel.