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Over a period of 13 years, hospital-associated infections and antimicrobial resistance declined simultaneously for common pathogens at U.S. Veterans Affairs (VA) medical centers, according to a large retrospective cohort study.

During 2007 through 2019, the overall infection incidence of nine common pathogens declined with an average annual percentage change (AAPC) of -2.2% (95% CI -3.2 to -1.2, P<0.0001), and the proportion of infections resistant to at least one key antibiotic class declined from about 58% to 47%, reported Thi Mui Pham, PhD, of the Harvard TH Chan School of Public Health in Boston, and colleagues.

Notably, the proportion of methicillin-resistant Staphylococcus aureus (MRSA) infections declined from 57.7% to 44.6% (P<0.0001) and vancomycin-resistant Enterococcus faecium infections decreased from 77.8% to 65.1% (P=0.052).

"The reductions in methicillin-resistant S. aureus, vancomycin-resistant E. faecium, and [hospital-acquired infections] underscore the importance of system-wide infection prevention and antimicrobial stewardship programs," Pham and colleagues wrote in .

Moreover, fluoroquinolone resistance declined in both proportion and incidence for most pathogens, particularly for E. faecium (AAPC -9.3%, P=0.0007), Enterococcus faecalis (AAPC -5.7%, P=0.0035), and S. aureus (AAPC -6.2%, P<0.0001).

The proportion of third-generation cephalosporin-resistant Pseudomonas aeruginosa (AAPC -10.1%, P<0.0001) infections decreased from 2007 to 2019, as well.

The study is unique because although previous studies have reported on antimicrobial resistance proportions, this study linked both antimicrobial resistance proportions and phenotypic incidence, i.e., the rate of susceptible and resistant infections.

Researchers evaluated over 990,000 clinical isolates collected from over half a million patients at 138 VA medical centers across the U.S. They collected data on S. aureus, E. faecium, E. faecalis, Acinetobacter sp, P. aeruginosa, Serratia marcescens, Enterobacter cloacae, Escherichia coli, and Klebsiella pneumoniae.

Although the proportion of infections resistant to a single key antibiotic class remained stable over time, the proportion resistant to multiple drug classes declined by 10 percentage points, from 39.5% in 2007 to 29.5% in 2019.

However, researchers also uncovered some concerning trends. For example, carbapenem resistance for E. cloacae infections rose from 1.1% in 2007 to 7.3% in 2019 (P<0.0001). And through 2019, E. coli infections resistant to third-generation cephalosporins more than doubled from 6.7% in 2007 to 15.3% (P<0.0001).

Also, incidence and resistance for some hospital-associated infections rose dramatically during the first 2 years of the COVID-19 pandemic. "From Jan 1, 2020 ... infection incidence trends reversed for [hospital-associated infections] in many pathogen-drug combinations," the authors commented.

This finding is mirrored to some extent in a 2022 CDC report showing that infections and deaths from seven antibiotic-resistant pathogens rose by 15% in 2020.

Of note, reductions in the incidence of infections resistant to antibiotics was not always linked to the proportion of resistant infections, Morgan Walker, MD and Sameer Kadri, MD, MS, both of the NIH Clinical Center in Bethesda, Maryland, wrote in an .

For example, "despite decreasing trends in the incidence of both carbapenem-resistant and carbapenem-susceptible Klebsiella pneumoniae phenotypes between 2020 and 2022, there was an increasing trend in the resistance proportion during the same period," the editorialists pointed out.

Morgan and Walker also noted that the study did not look at infection and antibiotic resistance trends in community-dwelling patients. "Although inpatient admissions might be a reasonable denominator to use in the assessment of the at-risk population for hospital-associated infections, it might not accurately capture the at-risk population for community-onset infection," they commented. This may have been especially pertinent during the COVID-19 pandemic when there was a decline in non-infectious routine hospital admissions, but an overall increase in antimicrobial resistance, they noted.

Researchers used electronic health records to analyze clinical microbiology data from all patients admitted to VA medical centers with acute care wards across the U.S. from February 2007 through March 2022. They gathered inpatient data on days of antibiotic therapy per 1,000 patient-days. They also identified antimicrobial resistance by resistance proportion and incidence of infections per 1,000 admissions classified as resistant or susceptible, or missing data. The most commonly identified pathogens were S. aureus, E. coli, and K. pneumoniae. Most cultures were from non-blood sites.

Pham and colleagues pointed out several important limitations of the research. As a VA study, the patient population differed from the general population in demographics, comorbidities, and healthcare-use patterns. The study was not able to fully evaluate multidrug resistance patterns. There was limited information about infection control practices, and system-wide implementation of antibiotic stewardship policies may have varied across facilities.

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