At least 65 cases of the coronavirus have been reported among World Health Organization staffers based at the agency’s headquarters in Switzerland, according to an email obtained by The Associated Press.

The internal document said about half of the infections involved employees who had been working from home, while others who contracted the disease had been working on-site in the Geneva offices. About 2,000 people typically work at the WHO headquarters building, according to the AP.

All staffers who have tested positive for the virus “are receiving the necessary medical attention and are recovering at home,” the WHO email said.

Of the total cases at the agency’s offices, 49 are believed to trace back to the last eight weeks, according to the email, which noted that the outbreak is in line with that of the Geneva area in general. The email did not identify the timeline of the other 16 cases.

“To my knowledge, the cluster being investigated is the first evidence of potential transmission on the site of WHO,” WHO chief of emergencies Michael Ryan told reporters Monday.

Maria Van Kerkhove, the WHO’s technical lead on the virus, added that “we have had some cases that have been associated with the premises. We do have some cases in the last week that are linked together.”

Van Kerkhove said she could not rule out that any of the cases were contracted outside the facility.

“There are possible ways in which they were infected outside of the premises. So we’re still doing the epidemiologic investigation with that,” she said, according to the AP.

While the email did not identify specific people who were infected, a WHO staffer with direct knowledge told the AP that one of the cases is an infection control specialist who is on the WHO director-general’s leadership team.

Two weeks ago, Director-General Tedros Adhanom Ghebreyesus announced he would self-quarantine after coming into contact with an infected person. Tedros did not identify where he came into contact with the person.