Corrections & clarifications: An earlier version of this story misstated which five states have no A-rated hospitals. Alaska should have been named rather than Arkansas.

Patients' risk of dying from medical mistakes, deadly infections and safety lapses have gotten much worse at the lowest ranked U.S. hospitals, underscoring Americans' need to check ratings of their local hospitals, new research released Wednesday shows.

The new analysis is based on data gleaned from about 2,600 U.S. hospitals since 2016. What the findings reveal is that some of the nation's most dangerous medical centers have become even riskier for patients.

"These are the avoidable deaths – the deaths that are accidental or the result of a mistake made in the hospital," said Leah Binder, the CEO of the non-profit Leapfrog Group, which issues grades hospitals based on safety and quality. "It doesn’t matter how sick you are – the surgeon and operating room team shouldn’t be leaving sponges or surgical tools in you."

Leapfrog assigns letter grades - from A to F - to hospitals and is a tougher grader than the federal government, which doesn't issue failing marks. The latest Leapfrog rankings, released Wednesday, give failing or near-failing classifications to 168 hospitals.

Among the hospitals with failing grades are United Medical Center in Washington, D.C, Hurley Medical Center in Flint, Mich., and St. John's Episcopal Hospital in Far Rockaway, N.Y.

The American Hospital Association, a trade group, defended its member hospitals, saying that improvements have been made. The group cited recent data that shows hospitals have been doing a better job at preventing infections and other safety problems that patients sometimes get during treatment. It said hospitals are "making important strides in making care safer."

Akin Demehin, AHA's director of quality policy, said Leapfrog's grades may not reflect recent hospital improvement efforts, adding "not all measures apply to all patients."

Hospitals that scored poorly also have claimed that the rankings are skewed because they treat sicker patients, whereas higher-graded hospitals have a healthier, more affluent clientele and are therefore less likely to have complications.

But Leapfrog, which has been grading hospitals since 2012, counters that some of their measurements, such as hospital infections, are risk adjusted to reflect sickness levels of patients.

Some medical errors, such as leaving instruments inside patients, should never happen no matter how sick the patient is, Binder said.

"Improving their safety record is something any hospital can do and they don’t have to have a lot of money or resources," she said. "They just have to put patients first."

Also Wednesday, the Armstrong Institute for Patient Safety and Quality at Johns Hopkins Medicine released its updated 2016 report on Leapfrog's grades and the increased death risk associated with them. It found some encouraging news: Although about 160,000 people die a year from the avoidable medical errors reflected in the Leapfrog's grades, that's still a drop from the 205,000 avoidable deaths estimated in 2016.

Other grades:

• About a third of the more than 2,600 hospitals graded received an A grade. Forty-one of them - including Brigham and Women's Faulkner Hospital in Boston and OhioHealth Methodist Hospital in Dublin, Ohio - have only gotten A's since Leapfrog started grading in 2012.

• About a quarter of hospitals got a B; 36% earned C's and 6% got a D grade. Patients at C-rated hospitals on average face an 88% greater risk of avoidable death, while those at B-rated hospitals on average face a 35% greater risk of avoidable death, the Armstrong Institute report said.

• The five states with the highest percentages of “A” hospitals were Oregon, Virginia, Maine, Massachusetts and Utah.

• There were no A-rated hospitals in five other states: Wyoming, Alaska, Washington, D.C., Delaware, North Dakota.

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People whose family members have suffered at average- or low-grade hospitals say they wish they had checked ratings.

When his 69-year-old mother went to a hospital for a partial hip replacement in 2009, Los Angeles comedy director Steve Burrows said he "had no idea what it was rated." Judie Burrows lost half of her blood and was taken to intensive care, where no one realized she had fallen into a coma, her son charged in a lawsuit and new HBO documentary Bleed Out.

Burrows was interviewed by USA TODAY after Leapfrog recommended him as someone who believes in the nonprofit's ratings.

The hospital where his mother was treated, Aurora West Allis Medical Center in Milwaukee, is rated C in the new Leapfrog ratings.

Judie Burrows, who suffered irreversible brain damage and could never return home, is now in long-term hospice. Despite an emergency trip with his wife to an F-rated hospital in California a few years ago, Burrows is now committed to only using A-rated hospitals.

"If a hospital is rated an F, it's an incredibly good indicator what’s going on at that hospital: what the culture is and what the quality and safety of that hospital is," Burrows said. "You're not going to go out for a D rated steak dinner or a chicken Alfredo rated C."

"Our hearts go out to the Burrows family, and our focus remains on providing the safest care and achieving the best outcomes for our patients," Aurora West Allis said in a statement. "While we applaud efforts to report and measure safety, we recognize that government and industry safety organizations use varying methodologies that don’t always reflect the quality of care provided."

Marian Hollingsworth of La Mesa, Calif., became a patient safety advocate after her father died in 2009 at a nursing home. She alleges that he succumbed to a staph infection that led to pneumonia, and that he also suffered from the effects of an anti-psychotic medication given without consent.

Last year, her husband, Ed, got sepsis in a hospital that was rated A by Leapfrog but soon dropped to a B.

"An A rating is certainly no guarantee that things will go well," Hollingsworth said. "I think having these rating systems definitely helps people get an idea of the quality of their hospital, but they still need to be vigilant while at the hospital."

While Hollingsworth supports hospital rating systems including Leapfrog's, she says she worries that hospitals “teach to the test” to get a good rating.

Leapfrog, started by employers and unions that wanted more public information about patient safety and quality, factors medical errors, infections and injuries into its grades. The ratings are based in part on patient responses to surveys, data provided to the Centers for Medicare and Medicaid Services, the American Hospital Association and voluntarily to the nonprofit.

More than 2,000 hospitals - at least 50% of those eligible - agree to provide the additional voluntary data on medication safety, hand hygiene, intensive care unit physician coverage and cesarean section section rates.

Hurley Medical Center spokeswoman Laura Jasso noted that the hospital, which received an F grade, doesn't provide any voluntary information, which she said "obviously" affects the grade.

Hurley, like United Medical Center, has a one-star rating on CMS' Hospital Compare site.

United Medical Center and St. John's Episcopal in Far Rockaway, New York, did not respond to a request seeking comment.

No matter what a facility is rated, Hollingsworth said consumers "should not assume hospitals are clean."

"It’s what you can’t see that can kill you," she said.