According to Central Valley Business Times:
The confidential information on the lost tape includes employee e-mails, investigative reports, background information on health care workers, the names of health care facility residents and some information on their medical diagnosis, and Social Security numbers for CDPH employees and some facility residents and health care workers.
The incident occurred when a CDPH field office in West Covina used the U.S. Postal Service to send the tape to the central office in Sacramento. The information was encrypted, and officials say there is no evidence that the information has been misused.