CDC, VA Authors Reject Calls to Lessen Interventions

SALT LAKE CITY—Concerned about methicillin-resistant Staphylococcus aureus, one of the most common causes of healthcare-associated infections, the VA piloted a MRSA prevention program in 18 VAMCs beginning in 2005.

Two years later, all 153 VAMCs had implemented the MRSA prevention program. The efforts included, among other components, admission screening for nasal MRSA carriage and using contact precautions such as wearing a gown and gloves for all interactions involving contact with the patient or the surrounding environment of those found to be carriers.

An article in the Morbidity & Mortality Weekly Report described the effect of that intervention, noting that, overall, the VA had significant success in driving down cases of MRSA, which can cause significant morbidity and mortality.1

Researchers tracked the incidence of MRSA and methicillin-susceptible S. aureus infections at 130 VAMCs from 2005 to 2017 and examined hospital-acquired MRSA colonization based on results of MRSA surveillance tests collected during the same period.

The study was led by the VA Salt Lake City, UT, Healthcare System and included participation from the national Centers for Disease Control and Prevention in Atlanta and VA national offices in Washington.

Researchers determined that S. aureus infections decreased by 43% overall during the study period (p<0.001). The decline was primarily driven by decreases in MRSA, which dropped by 55% (p<0.001), although MSSA decreased by 12% (p = 0.003). Hospital-onset MRSA and MSSA infections decreased by 66% (p<0.001) and 19% (p = 0.02), respectively.

At the same time, community-onset MRSA infections decreased by 41% (p<0.001), but MSSA infections showed no significant decline. Acquisition of MRSA colonization decreased 78% during 2008–2017 (17% annually, p<0.001). MRSA infection rates declined more sharply among patients who had negative admission surveillance MRSA screening tests (annual 9.7% decline) compared with those among patients with positive admission MRSA screening tests (4.2%) (p<0.05), the study reported.

“Significant reductions in S. aureus infection following the VAMC intervention were led primarily by decreases in MRSA,” the authors wrote. “Moreover, MRSA infection declines were much larger among patients not carrying MRSA at the time of admission than among those who were. Taken together, these results suggest that decreased MRSA transmission played a substantial role in reducing overall S. aureus infections at VAMCs.”

Prevention Strategies

The researchers cautioned against any victory dances, however, explaining, “Recent calls to withdraw infection control interventions designed to prevent MRSA transmission might be premature and inadvisable, at least until more is known about effective control of bacterial pathogen transmission in healthcare settings. Effective S. aureus prevention strategies require a multifaceted approach that includes adherence to current CDC recommendations for preventing not only device- and procedure-associated infections, but also transmission of health care–prevalent strains”.

The study sought to analyze potential mechanisms that could explain discordant MRSA and MSSA trends in hopes that those could provide insights for S. aureus prevention strategies.

The authors suggested that one potential explanation is that the observed trends represent “an artifact of differential detection bias, by which MRSA-infected patients would be progressively less likely than would MSSA-infected patients to have cultures obtained over the course of the study period. There is no obvious reason that likelihood of obtaining a diagnostic culture in patients with suspected infection would differ according to a provider’s clinical suspicion of MSSA versus MRSA, and there was no change in rate of diagnostic cultures obtained over the study period, nor was there any difference in diagnostic culture rate based on admission MRSA carriage status.”

Another possibility, the researchers posited, is that shifts in S. aureus epidemiology might have influenced the observed trends. They noted, however, that “data describing the national MRSA experience do not support this hypothesis. Population-based surveillance data from CDC’s Emerging Infections Program show that, although rates of health care-associated MRSA infection rates have been declining, community-associated MRSA rates have remained unchanged since 2005 (6). In addition, almost all MRSA reductions resulted from decreases in USA100, a strain associated with health care system transmission.”

The study also cited only modest reductions in USA300, a strain associated with community transmission, bolstering the argument that, without replacement by other strains, successful interruption of MRSA transmission in healthcare settings is having a significant effect.

“Infection control interventions might produce differential trends in MRSA and MSSA infection rates,” the study authors pointed out. “Two broad approaches to preventing health care-associated infection include reducing the likelihood of invasive disease given colonization or exposure and decreasing transmission of pathogens (preventing infection by avoiding colonization or exposure in the first place).”

The study noted that the VA adopted both of those strategies, adding, “Similar to programs elsewhere, the VA system implemented bundled interventions designed to prevent device- and procedure-related infections (e.g., central line-associated bloodstream and surgical site infections). However, if such interventions were primarily responsible for the observed S. aureus trends, MSSA and MRSA rates would have been expected to have been affected approximately equally.”

Researchers emphasized that exactly how transmission was prevented is difficult to determine with precision, partly because multiple interventions were occurring simultaneously. One factor was changes in antibiotic use. The study cited evidence that fluoroquinolone use is associated with increased MRSA colonization, and the reduction in fluoroquinolone use could contribute to selective reduction in MRSA because it is more commonly fluoroquinolone-resistant than MSSA. While the VA did observe a substantial reduction in fluoroquinolone use, according to the report, fluoroquinolone reductions did not begin until 2009, and that was after substantial MRSA reductions had already occurred.

“The significant reduction in S. aureus infection observed across VAMCs, driven primarily by a decrease in MRSA infection rates, offers important insights that can inform national S. aureus prevention strategy,” the authors concluded. “Although the causal relationship between specific components of the VA-wide infection control intervention and the reduction in infection rates is difficult to determine with precision, it seems likely that decreased MRSA transmission played a substantial role.”

The article argued against calls to withdraw infection control interventions developed to prevent MRSA transmission. Critics have called efforts such as contact precautions premature and inadvisable.

“Hospitals should reconsider best use of contact precautions for endemic MRSA and VRE in the context of a broad approach to infection control targeting the highest-value interventions,” wrote Daniel J. Morgan, MD, MS, of the VA Maryland Healthcare System and the University of Maryland School of Medicine, both in Baltimore, and colleagues. “It is time for the CDC to update its 2007 guideline. Legal mandates and metrics for active surveillance cultures should be retired.” The Viewpoint was published in 2017 in JAMA.2

“Adherence to CDC recommendations for antimicrobial stewardship, preventing device- and procedure-associated infections and interrupting transmission of health care-prevalent strains (e.g., use of contact precautions for MRSA) continue to be a mainstay of S. aureus prevention,” the authors of the recent MMWR article argued, however.

1 Jones M, Jernigan JA, Evans ME, Roselle GA, Hatfield KM, Samore MH. Vital Signs: Trends in Staphylococcus aureus Infections in Veterans Affairs Medical Centers — United States, 2005–2017. MMWR Morb Mortal Wkly Rep. ePub: 5 March 2019. DOI:

1 Morgan DJ, Wenzel RP, Bearman G. Contact Precautions for Endemic MRSA and VRE: Time to Retire Legal Mandates. JAMA. 2017;318(4):329–330. doi:10.1001/jama.2017.7419