Cases of methicillin-resistant Staphylococcus aureus (MRSA) infections acquired in U.S. hospitals dropped nearly 54% from 2005-2011, according to a new government study.

That good news came as the Centers for Disease Control and Prevention issued a separate report cataloging depth and variety of drug-resistant bacterial threats, concluding that they kill at least 23,000 people and add $20 billion in health care costs a year.

In a report published Monday in the Journal of the American Medical Association, CDC researchers estimated a general decline of about 28% in severe MRSA infections, falling to 80,461 in 2011, after rising at an alarming rate in the previous decade.

“Certainly there has been a big focus on trying to reduce health care-associated infections like MRSA in many hospitals and health care settings,” said study lead author Dr. Raymund Dantes, a former CDC epidemiologist and current associate professor of hospital medicine at Emory University. “We certainly hope that this dramatic decrease in MRSA infections, especially in the hospital setting, suggests that these efforts are paying off.”

MRSA is a bacteria that has become resistant to antibiotics used to treat staph infections. In health care settings, it commonly occurs in patients that have had invasive procedures, such as surgeries or intravenous tubing. In communities, infection is more likely to appear as a boil, which is transmitted through skin contact.

According to CDC figures, between 1995 and 2005, the estimated number of hospitalizations due to MRSA increased from 127,036 to 278,203, with an average of 5,500 deaths a year during that time.

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The rapid rise in cases prompted many hospitals to re-evaluate their hygiene protocols, which has been a major factor in the decrease between 2005 and 2011.

“Many institutions have dramatically lowered their rates of bloodstream infection, which is a big subset of MRSA infections,” said Dr. Scott Flanders, director of the University of Michigan's Hospital Medicine program. “Overall, all the numbers were down, but it sounds like one of the largest burdens continues to be these patients who were recently in the hospital, which raises the possibility that we are shifting cases from hospital-onset to onset outside the hospital.”

In other categories, however, the progress was more modest.

Rates of health care-associated community-onset infections — or infections that have occurred within 12 weeks of a hospital stay — fell by 28%m while the rate of community-onset infections had the smallest decrease, falling by only 5%.

Health care exposure has been one of the leading risk factors in contracting severe cases of MRSA infection, so higher rates of other risk factors within these groups may help explain the smaller declines, Dr. Dantes said.

“There are higher rates of diabetes, there is a higher rate of HIV, and there is a higher rate of intravenous drug use among folks with these community-associated infections,” Dr. Dantes said. “So some of them can be explained by these risk factors, but certainly more research needs to be done to determine the best recommendations for preventing these types of infections.”

In a briefing with reporters, CDC Director Dr. Tom Frieden called the broader array of antibiotic-resistant infections one of the most serious health threats. C. difficile alone, the CDC said, is associated with 250,000 hospitalizations and 14,000 deaths a year.

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“Without urgent action now more patients will be thrust back to a time before we had effective drugs,” Dr. Frieden said.

The CDC is recommending four actions to fight the threat:

• Prevent the spread of infections through immunization, hygiene and other measures in order to reduce the use of antibiotics.

• Track infections and their causes to drive prevention strategies.

• Reduce antibiotic use, about half of which is deemed unnecessary.

• Develop new antibiotics and diagnostic tests.

“We talk about a pre-antibiotic era and an antibiotic era; if we're not careful, we'll soon be in a post-antibiotic era and in fact for some patients and some microbes we are already there,” Dr. Frieden said.

Steven Ross Johnson writes for Modern Healthcare, a sister publication of Business Insurance.