Ben Margot / AP

Bay Area commuters warned of possible measles exposure on BART

Contra Costa County says infected commuter rode train between Lafayette and San Francisco stations in early February

Public health officials warned on Wednesday that thousands of commuters on the Bay Area Rapid Transit system (BART) may have been exposed to measles after an infected employee of the Mountain View, California-based company LinkedIn rode the trains to and from work in early February.

Contra Costa County officials said in a press conference that a person diagnosed with measles rode BART to and from work, from the Montgomery Street station in San Francisco to the Lafayette stop in Contra Costa County from Feb. 4 through 6. 

The measles-infected person, whom the officials did not identify, traveled during rush hour on the mornings and evenings of those days, and also dined at the E & O Kitchen and Bar in San Francisco on the evening of Feb. 4. Officials warned that because the highly infectious measles virus can stay in the air for two to four hours and BART trains travel all over the Bay Area, unvaccinated riders are at risk.

LinkedIn told the Associated Press in a statement that it was informed on Tuesday that an employee based in its San Francisco office was diagnosed with measles.

"Measles is circulating in the Bay Area, and we don't know yet where this person was exposed," said Erika Jenssen, chief of communicable diseases at Contra Costa County's public health agency, in a release. "The ongoing measles outbreak in California highlights the need for people to be vaccinated, and this is just another example of how interconnected our region is and how important it is for everyone to be up to date on their immunizations."

Since Jan. 1, 121 people have been infected in California and 17 other U.S. states in the current measles outbreak, according to the latest figures from the Centers for Disease Control. Public health officials have linked the outbreak to exposures at Disneyland theme parks near Los Angeles last December.

The respiratory disease is incredibly contagious and is marked by a cough, runny nose and a rash. Ninety percent of people close to an infected person who is not immune will come down with the disease, according to the CDC.

While the CDC credits widespread inoculation for the fact that the measles has been considered eliminated from the U.S. since 2000, a significant number of parents in some states, including California, Oregon and Vermont, have increasingly sought exemptions from vaccinating their children due to religious or personal beliefs.

When nearly all of a population is vaccinated, it protects the small number of individuals in whom the vaccine doesn’t work and those who can’t get vaccinated — babies under 12 months or those with medical conditions that weaken their immune systems. When overall measles vaccination rates in a population fall below the recommended 92 to 94 percent, this so-called herd immunity is lost. That’s why public health experts are so concerned about low vaccination rates in certain parts of California.

January study of the electronic health records of more than 154,000 Kaiser Permanente patients in northern California found that there were certain counties where parents who were refusing or delaying vaccinating their kids had clustered—places that would be prime targets for measles outbreaks if an infected person were to visit. For example, the researchers found that in areas of the East Bay, Marin, Sonoma and Napa, as many as 23 percent of kids had not been immunized. In some other parts of San Francisco and the East Bay, up to 13.5 percent of kids didn’t receive vaccinations.

To counter the increasing number of parents who have sought exemptions from vaccinating their children due to personal beliefs, California lawmakers recently introduced legislation that would require parents to vaccinate all school children, except for those who have pre-existing medical conditions that make it too dangerous. If passed, California would join two other states, Mississippi and West Virginia, with such stringent restrictions.

Dr. Tomas Aragon, health officer for the city and county of San Francisco, stressed the effectiveness of the measles vaccine in a press release and urged people to get vaccinated: "While we are concerned about the current outbreak in California and its potential to spread, we cannot emphasize enough that the solution is simple and available: be vaccinated."

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