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Good news: prevention efforts in healthcare settings helped cut infections attributable to certain bacterial pathogens, studies suggested.

Methicillin-resistant Staphylococcus aureus (MRSA) and other infections trended downward in the last decade, mostly driven by reductions in hospital-associated cases, CDC researchers and partners reported in two papers in the New England Journal of Medicine.

But much work remains ahead, according to Ferric Fang, MD, of the University of Washington School of Medicine in Seattle, and Robert Schooley, MD, of the University of California San Diego.

"We cannot afford to be complacent about recent progress in the health care setting, because resistant pathogens are still too common in most institutions, and favorable trends can be readily reversed. It will be more difficult to control antimicrobial resistance in the community, and innovative approaches are needed," Fang and Schooley cautioned in an .

Multidrug-Resistant Bacteria: Good News and Bad News

In the first study, certain antimicrobial-resistant infections were found to be less common in recent years.

Together, six drug-resistant pathogens were responsible for an estimated 622,390 infections -- 83% community-onset and 17% hospital-onset -- nationally in 2017 among hospitalized patients, according to .

Some, not all, infections showed decreased incidence from 2012 to 2017:

• MRSA infections fell from 114.18 to 93.68 cases per 10,000 hospitalizations

• Vancomycin-resistant enterococcus infections dropped from 24.15 to 15.76 per 10,000

• Carbapenem-resistant acinetobacter species infections fell from 3.33 to 2.47 per 10,000

• Multidrug-resistant P. aeruginosa infections decreased from 13.10 to 9.43 per 10,000

• Carbapenem-resistant Enterobacteriaceae infections did not change much, going from 3.36 to 3.79 cases per 10,000

• Infections from extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae increased from 37.55 to 57.12 cases per 10,000

"Antimicrobial resistance remains an important threat to health in the United States," the investigators concluded, hypothesizing that community-onset cases were to blame for the unfavorable uptick in ESBL infections.

Nevertheless, it does appear that increased efforts to prevent infections from multidrug-resistant organisms -- namely, the 2015 National Action Plan emphasizing antimicrobial stewardship programs, surveillance, improved diagnostic tests, new treatment approaches, and international collaboration -- have been "worthwhile," according to Fang and Schooley.

A high priority, they said, continues to be the search for new strategies to treat infections by drug-resistant pathogens.

Jernigan and co-authors explained that the study was based on patients hospitalized in 890 U.S. short-term acute care hospitals in 2012-2017. The study included 41 million hospitalizations, accounting for over 20% of U.S. hospitalizations annually.

The six antibiotic-resistant pathogens were present in 292 clinical cultures per 1,000 patient-days. Most infections were caused by MRSA and ESBL-producing species (52% and 32%, respectively).

The researchers acknowledged that they couldn't be sure if the microbiology culture results in the study represented true infections.

"Second, we were only able to categorize community-onset and hospital-onset cases according to the timing of culture relative to admission and were therefore not able to determine whether community-onset cases were attributable to previous health care exposures," the team wrote.

Another limitation, the authors said, was that the hospitals included were not randomly selected and therefore may not have been nationally representative.

C. difficile Infections Down

The incidence of healthcare-associated Clostridioides difficile infection went down in recent years with no accompanying change in community-associated infections, a showed.

Alice Guh, MD, MPH, also of the CDC, and colleagues estimated the national burden of C. difficile infection to be 476,400 cases in 2011 and 462,100 in 2017, a decrease of 24% after accounting for new higher sensitivity of nucleic acid amplification tests (NAATs).

"In contrast, a indicated that the prevalence of healthcare-associated C. difficile infection had not changed as compared with 2011; however, the survey did not account for increased NAAT use, which could have masked a true reduction in C. difficile infection," the team wrote.

Health care-associated C. difficile infections decreased by 36% from 2011 to 2017, the investigators reported. "The decrease in health care-associated C. difficile infection probably reflects a decline in both cases with an onset associated with a long-term care facility and hospital-onset cases."

"Several factors probably contributed to the decrease in health care-associated C. difficile infection, including a decline in ribotype 027, which might be partly driven by reduced fluoroquinolone use in U.S. hospitals," the investigators continued.

On the other hand, there was no change in community-associated infections.

"Continued efforts are needed to improve infection prevention and diagnostic and antibiotic stewardship in both inpatient and outpatient settings," Guh and colleagues wrote. "The development of a C. difficile vaccine and exploration of innovative strategies, such as gut microbiome restoration for primary prevention of C. difficile infection, might also further reduce the burden of C. difficile infection."

Providing data for the study was the CDC's , a population-based surveillance program covering 35 counties in 10 states. Nationwide infection estimates were extrapolated from 10 sites, which had reported 15,461 C. difficile-positive stool samples in 2011 and 15,512 in 2017.

Healthcare-associated infections were defined as those with onset in a healthcare facility or associated with recent admission to one; all others were classified as community-associated infections.

Hospitalizations for C. difficile infection decreased by 24%, Guh's team estimated, whereas adjusted estimates of the burden of first recurrences and in-hospital deaths did not change significantly.

The investigators acknowledged that some infections may have been missed by the CDC over the course of the study.