On Friday, Contra Costa County officials mailed letters to county hospital patients whose names unintentionally appeared online in a public document. Officials said the incident involves patients who were relieved of medical debt last year by county supervisors. An agenda item posted online contained more than 5,000 patient names and financial records, but no medical information. County Administrator David Twa said that the names have been redacted and that the state Department of Public Health was notified. Twa added that the county started an internal investigation last week.