SAN FRANCISCO — A hospital that lost control of a computer containing the names, birth dates and medical record numbers of 500,000 patients going back to the 1980s did not violate California’s Confidentiality of Medical Information Act, a California appellate court ruled Wednesday.

Names on a hospital patient index are not “medical information” if they’re not coupled with medical histories, condition or treatment, the Fourth District Court of Appeal ruled. The decision reversed a trial court ruling that had exposed Eisenhower Medical Center in Riverside to as much as $500 million in statutory damages.