A U.S. evacuee from China infected with the coronavirus was mistakenly released from a San Diego hospital after an initial test came out negative, local health officials said Monday.

The patient arrived at the Marine Corps Air Station Miramar in San Diego last week from Wuhan, China, the epicenter of the outbreak that has left more than 1,000 dead and infected more than 42,000 in mainland China as of Tuesday.

The patient and three others were hospitalized after showing symptoms of the virus, but initial tests by the Centers for Disease Control and Prevention returned negative results for all four patients, who were then released and taken to quarantine facilities at Miramar Sunday, where they were told to stay for 14 days.

Further testing by the CDC returned a positive result for the coronavirus, and the patient was sent back to UC San Diego Health for observation and isolation Monday, according to CNN.

On Monday, a second person was transported to the UC San Diego Health center from Miramar for evaluation. It’s not clear whether the second patient was one of the original four tested.

The San Diego Union-Tribune reports UC San Diego Health said that even though the infected evacuee was accidentally released, all proper protocols were followed.

The hospital says both patients are doing well and are experiencing minimum symptoms.

At least 13 cases of coronavirus have been confirmed in the U.S., with seven in California. Arizona, Illinois, Massachusetts, Washington and Wisconsin have all reported cases.