As Google fights criticism that it has let anti-vaccine disinformation flourish on its platform, the tech giant’s Silicon Valley campus, where thousands work, is now confronting its own in-house case of measles as the virus resurges across the United States.

In an email sent to some employees last week and obtained by BuzzFeed News, a staff doctor at Google wrote that a worker who had recently been in one of its Mountain View, California, buildings had been diagnosed with measles.

David Kaye, an occupational medicine physician at Google, wrote that the worker had been in the office on 1295 Charleston Road April 4.

“We have been working with the Santa Clara County Public Health Department and they would like us to share this measles advisory, which contains information on measles, exposure risks and actions to be taken,” Kaye wrote April 13, adding that “this note is just a precaution.” Neither Kaye nor Google immediately responded to requests for comment.

A spokesperson for the county’s public health agency confirmed Wednesday afternoon that an unnamed adult resident of San Mateo County “who visited Google” had contracted measles. The case is unrelated to previous cases in Santa Clara County, and there is no additional public health risk, according to the agency.

The dangerous virus was eliminated from the US in 2000 — but there are now 555 cases across 20 states, the CDC said this week. New York City has declared a local outbreak to be a public health emergency and issued a mandatory vaccination order.

In Santa Clara County, which includes Mountain View, there are four confirmed cases of measles, public health officials said Tuesday.

Even though measles is highly contagious, the warning about the diagnosed employee has not been universally circulated within Google or its parent company, Alphabet. Five employees told BuzzFeed News they had not received the email or been otherwise told about the potential exposure.

The source who sent BuzzFeed News the email said they believed it went to everyone who worked in the 1295 Charleston building. And some employees who received the original email posted it on internal Google groups or forwarded it to colleagues in other buildings in case they recently visited 1295 Charleston, the person said.

The building is the home office for a number of Google executives. It’s unclear how many people work in the building.

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