More than half of 26 general, acute-care hospitals in or near San Francisco earned mediocre or poor grades for keeping patients safe, according to new research.

The Leapfrog Group, a national nonprofit organization that assesses hospital safety performance, released its 2019 findings Wednesday for 2,600 hospitals across the country, assigning them A through F letter grades. The researchers looked at inadequate safety procedures, incidence of deadly infections and medical mistakes, such as leaving a sponge or a clamp in a surgery patient.

We wanted to see how local hospitals in the report compared, so we chose those in a 25-mile radius of downtown San Francisco. Of the 26 hospitals, six received A's, four got B's, 12 C's and four were marked D's. None earned a failing grade.

When compared to "A" hospitals, patients receiving care at "D" hospitals faced a 92 percent greater chance of avoidable death, according to Leapfrog. For "C" hospitals the risk was 88 percent greater. "B" hospital patients faced a 35 percent greater risk.

"These are the avoidable deaths – the deaths that are accidental or the result of a mistake made in the hospital," Leapfrog CEO Leah Binder told USA Today. "It doesn't matter how sick you are – the surgeon and operating room team shouldn't be leaving sponges or surgical tools in you."

The Centers for Disease Control and Prevention notes that at any given time, about one out of 31 patients in a hospital has an infection caused by a hospital or other health-care provider.

Overall, the marks for San Francisco-area hospitals declined since Leapfrog's 2017 report. Twelve hospitals declined by one grade and three dropped two grades. Seven remained the same.

Most-improved awards went to St. Mary's Medical Center in San Francisco, Seton Medical Center in Daly City and Kaiser San Leandro, each up two grades.

To see all the rankings of all 26 hospitals, check out the gallery. Besides their letter grade, we included each hospital's results in three sample categories (Leapfrog uses a total of 28 safety measures in compiling its findings):

Methicillin-resistant Staphylococcus aureus (MRSA) infection, an infection often contracted during hospital stays;

Death from treatable serious complications (deaths per 1,000 people who had complications);

Dangerous bed sores (per 1,000 patients discharged).

Critics of Leapfrog's survey claim the results are skewed because low-scoring hospitals in poor areas often have a less healthy clientele than that of hospitals in affluent communities. But Leapfrog maintains that some of its measurements, like hospital infections, are risk-adjusted to reflect patient sickness levels.

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Nationally, an estimated 160,000 people die each year from avoidable medical errors. That's down from an estimated 205,000 avoidable deaths in 2016, according to Leapfrog.

Leapfrog only measured hospital safety, not quality. For example, a hospital could have the top cardiothoracic surgery team in its region, but still receive low marks because of its safety track record.

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Read Mike Moffitt's latest stories and send him news tips at moffitt@sfgate.com.

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