Four York County Sheriff’s Office and county government workers have tested positive for COVID-19, forcing both agencies to offer voluntary testing to all employees and inmates, the sheriff’s office said Thursday.

The Maine Center for Disease Control and Prevention has opened an outbreak investigation into the outbreak, inspecting the building that houses the sheriff’s office, York County Jail and county government and assisting workers there, spokesman Robert Long said.

When news of the positive tests came Thursday, workers began “enhanced cleaning” of the facilities, which had already closed lobbies and canceled prisoner visitations as precautions against the spread of the coronavirus. No interruption of services has occurred, officials said.

One worker was sent home after saying he felt ill, officials said.

The four cases are among 20 new coronavirus cases reported on Thursday. Thursday’s report brings the total coronavirus cases in Maine to 4,253. Of those, 3,812 have been confirmed positive, while 441 were classified as “probable cases,” according to the Maine CDC.