Twenty-three patients at San Francisco's Laguna Honda Hospital and Rehabilitation Center endured systemic abuse at the hands of six of the hospital employees, the Department of Public Health alleged Friday.

The victims live in two wards at the public hospital that primarily serves dementia patients and were subjected to alleged physical and verbal abuse between 2016 and January 2019, according to the health department. An investigation by DPH and the city attorney’s office that started in February also found that some patients were regularly given both prescription and nonprescription drugs intended to sedate them. The patients ranged in age from 30 to around 100.

The public, city-run facility serves as a live-in hospital, nursing home and rehabilitation center for 780 patients.

Health officials said Friday that the six alleged abusers took photos and videos of themselves engaging in the abuse — including having sexualized conversations with patients. The alleged abusers then exchanged those photos and videos over text messages.

Officials uncovered the alleged abuse following an investigation into an unrelated dispute between two employees. That investigation unearthed some of the text-message exchanges, the health department said. The department could not elaborate on whether one of those employees was tied to the abuse scandal, citing the confidentiality of personnel issues.

The patients and their families and caretakers all have been notified of the abuse.

None of the six alleged abusers work for Laguna Honda today, but DPH could not comment. The hospital’s chief executive, Mivic Hirose, has resigned. The hospital’s chief of quality management — who oversees Laguna Honda’s compliance with patient-care standards — has been placed on administrative leave and will not return to the position, the health department said. The city has brought in administrators from Zuckerberg San Francisco General Hospital to manage Laguna Honda’s quality management temporarily.

Maggie Rykowski, the health department’s chief integrity officer and director of the Office of Compliance and Privacy Affairs, will serve as the hospital’s acting CEO until a full-time replacement is found.

The California Department of Public Health is also conducting an ongoing investigation. Back in 2017, that agency fined Laguna Honda $100,000 for safety violations that led to a patient’s death. In November 2014, a hospital staffer failed to properly lock a patient’s wheelchair and left the patient alone on a curb during an outing to a movie theater. The wheelchair rolled off the curb and the patient fell to the ground face-first, causing a severe head injury and a broken hip. The patient died two weeks after the incident.

The San Francisco Police Department’s Special Victims Unit began its own criminal investigation into the abuse in February after being contacted by the city attorney’s office, SFPD spokesman David Stevenson said Friday.

Mayor London Breed said at a news conference Friday that she and the health department were “committed to restoring trust” among the hospital’s patients and their caregivers. “We are better than this,” she said.

Breed’s own grandmother, whom she said suffered from dementia, lived at Laguna Honda for years, until she died in 2016. She praised the hospital’s staff for the care her grandmother received, but in a statement, she called the revelations of the abuse “profoundly hurtful, offensive, and heartbreaking for so many of us who care deeply about this hospital.”

Board of Supervisors President Norman Yee said he was “super outraged with what has occurred,” and pledged to call a hearing to find ways “to prevent such abuse.” The hospital is located in District Seven, which Yee represents. He said that he has family members and friends who are current or former patients there. “For this to occur on our watch, I don’t have words to express how upset I am.”

DPH Director Dr. Grant Colfax apologized to the patients and their families, and outlined several steps the department has already taken in response to the abuse allegations. In addition to the personnel changes, hospital staff have been retrained to prevent and report patient abuse. Colfax said he was concerned about “a culture of silence” at the hospital, where staff turn a blind eye to abuse. The department also plans to submit a “turnaround plan” for the hospital within 60 days to the mayor and the Health Commission, which governs the department.

“People with dementia get picked on because they’re easy targets and no one believes them,” said Pat McGinnis, executive director of California Advocates for Nursing Home Reform.

Reports of the abuse at Laguna Honda were distressingly similar to those her organization sifts through on a daily basis, she said. But what did stand out, she said, was “the extent of it — how long it went on and how many people were involved. It’s absolutely disgusting and horrible.”

Dominic Fracassa is a San Francisco Chronicle staff writer. Email: dfracassa@sfchronicle.com Twitter: @dominicfracassa