Nursing homes and senior care facilities in the Bay Area and beyond are banning or restricting visitors in an effort to prevent the spread of the coronavirus — a dramatic step they hope will protect a population most vulnerable to infection, but that could take a heavy toll on families.

It comes amid growing concerns that the virus, which has killed more than 4,200 people worldwide, may eventually spread into senior communities, where the risk of death is significantly greater. That concern became a horrifying reality for patients in the Life Care Center of Kirkland in Washington, where 19 deaths are connected to a coronavirus outbreak.

“A lot of these people have heart disease or pulmonary diseases, which puts them at risk of developing complications,” said Dr. Michi Yukawa, a geriatrician and medical director of the Community Living Center at the San Francisco VA Medical Center. “Their immune system is not as robust as younger adults or even children to be able to fight off viral infections.”

Yukawa, who oversees about 87 patients, said the center is allowing visitors only for patients who are in hospice. Everyone who walks in — including staff — gets their temperature checked at the entrance, she said.

“This is to protect the people who are here,” Yukawa said. “These are the folks that are most vulnerable and they are the ones that are dying, not the healthy young people or children. They’re the No. 1 priority.”

The Centers for Disease Control and Prevention said older adults and people with heart disease, diabetes and lung disease are most at risk of getting very sick from the illness.

A resident in an assisted living facility in Sacramento County with an underlying health condition died of complications from the virus, health officials there announced Tuesday. The person was 90 or older, officials said.

The virus has hit hard in the Bay Area, where at least 95 people have contracted the virus. Santa Clara County had 45 cases as of Tuesday afternoon — the largest number of any region in the state. Officials there responded by banning gatherings of more than 1,000 people for three weeks, including sports events and concerts.

Gov. Gavin Newsom on Tuesday said protecting senior communities is the state’s top priority. Officials are working to develop guidelines for sanitation and isolation protocols for nursing homes and senior living facilities, he said.

“We want to make sure our seniors are protected. They’re our top priority,” Newsom said during a press conference in Sacramento. “To the extent we can avoid large social interaction with our senior community, that would be the top priority.”

Seniors are particularly vulnerable to infection because of their age and pre-existing conditions such as heart or lung disease, diabetes or cancer, according to health experts and physicians. Those who contract the virus are at a higher risk of death. Preliminary data show the fatality rate among older adults is 15% or greater, far higher than in other age groups, according to the American Health Care Association and the National Center for Assisted Living, which released a series of recommendations for skilled nursing centers across the U.S.

“There’s a growing body of evidence from the World Health Organization and countries like China that this virus is especially threatening to older adults and those with underlying health conditions, and our long term care residents are both,” said the health care association in Washington, D.C., in a statement Tuesday.

The association, a nonprofit federation of state health organizations, has “strongly recommended” that nursing homes restrict and monitor visitors.

Sarah Lawton said her husband, Dominic Chan, got a call from staff at San Francisco’s Laguna Honda Hospital Saturday saying visitors would no longer be allowed. Chan’s mother, Teresa Chan, 79, has lived at the facility for nearly two years, she said.

Family members normally visit Chan about three times a week, said Lawton, a San Francisco resident. She’s worried the new regulation will cause patients to feel isolated.

“But clearly (the virus) is very concerning,” she said. “This is the population that’s most vulnerable. We’re not questioning that.”

Laguna Honda — the huge skilled nursing and rehabilitation center owned and operated by the San Francisco Department of Public Health — announced Tuesday that it’s restricting access to essential personnel under an order by the city and county.

“The age, physical condition, and health of a significant majority of Hospital residents places those residents at high risk of experiencing serious health complications from COVID-19 infection, including death,” the order said.

Chronicle staff writer Anna Bauman contributed to this report.

Tatiana Sanchez is a San Francisco Chronicle staff writer. Email: tatiana.sanchez@sfchronicle.com. Twitter: @TatianaYSanchez