The Leapfrog Group is a national nonprofit organization driving a movement for giant leaps forward in the quality and safety of American health care.
The rating was given by a watchdog group that surveys hospitals on several areas including everything from housekeeping to food services.
Leapfrog cited San Francisco General, a public safety net hospital, for being below average at preventing surgical site infections after colon surgery and for allowing unsafe objects to be left in a patient's body, among other factors.
CHOMP improved its score over past year, when it received B's in both spring and fall of 2016. "Our families, neighbors, colleagues, and friends deserve a hospital that puts safety and patient care above all else", Koosnman said in a statement.
In Philadelphia, Hahnemann University Hospital, Jeanes Hospital, Pennsylvania Hospital and Penn Presbyterian Medical Center earned a "B", and Aria Health - Frankford Campus, Aria Health - Torresdale Division, Einstein Medical Center, Mercy Health System - Nazareth Campus and Temple University Hospital received "C" grades, according to Philly Voice. Kaiser Permanente Riverside Medical Center also notched a B. Parkview Community Hospital Medical Center and Hemet Valley Medical Center each received a D.
Leapfrog Group spokeswoman Erica Mobley said patient safety errors include accidents, injuries and preventable infections and that those errors are the third leading cause of death in the country.
Leapfrog named Natividad a "Top Hospital" in December 2016, one of 11 in the state and the only hospital in Monterey County to receive the honor.
The best scores were evenly split in Orange County, with 37 percent receiving an A and 37 percent a B. Four local hospitals were not graded - Orange County Global Medical in Santa Ana, Anaheim Global Medical Center, Chapman Global Medical Center in Orange and South Coast Global Medical Center in Santa Ana.
In Leapfrog's report card, some performance measures are risk-adjusted for patient severity and income so hospitals aren't penalized for admitting sicker, poorer patients.
Methodist Dallas, Methodist Mansfield, and Medical City Las Colinas have received the highest rating for patient safety for spring 2017 by The Leapfrog Group, an independent hospital watchdog.
"The information obtained by Leapfrog about Memorial Hospital of Gardena is not current data and is not congruent with the data reported by participating hospitals", said spokeswoman Amie Boersma via email. But diarrheal infections in California hospitals have increased 8 percent above a national benchmark since 2011.
Some hospital industry officials have criticized Leapfrog's letter grades as too simplistic for a complex issue and as potentially misleading for patients.
In Santa Cruz, Dominican Hospital received an "A" overall score. UC Irvine Medical Center in Orange received an A. Providence's Burbank hospital had a higher-than-expected rate of patients who developed serious breathing problems and caught antibiotic-resistant infections, according to Leapfrog. Leapfrog did not immediately respond to a request to explain why they were not included.
California's Office of Statewide Health Planning and Development also offers data on hospital quality and patient outcomes.