What happened
Staphylococcus aureus is among the most common causes of health care–associated infections, and causes much illness and death. In 2005, facing high rates of methicillin-resistant S. aureus (MRSA), the U.S. Department of Veterans Affairs piloted an MRSA prevention program in 18 VA medical centers. By October 2007, all 153 had adopted it. Among other things, the program:
- screened every admission for MRSA carried in the nose;
- put carriers under contact precautions — a gown and gloves for any contact with the patient or their surroundings.
Researchers then tracked infections at 130 VA hospitals from 2005 to 2017.
The results
| Infections | Change, 2005–2017 | Per year |
|---|---|---|
| All S. aureus | −43% | −4.7% |
| MRSA | −55% | −7.3% |
| MSSA (methicillin-susceptible) | −12% | −1.2% |
| Hospital-onset MRSA | −66% | −8.9% |
| Hospital-onset MSSA | −19% | −1.7% |
| Community-onset MRSA | −41% | −4.8% |
| Community-onset MSSA | no significant change |
- Bloodstream and other infections fell by similar amounts.
- After discharge: community-onset MRSA infections fell most in the 30 days after leaving hospital. Falling community-onset MRSA accounted for 48% of the drop in MRSA and 40% of the drop in all S. aureus infections.
- Picking up MRSA: patients acquiring MRSA in hospital fell 78%, from 6.8 to 1.5 per 1,000 patient-days at risk between 2008 and 2017.
- Carriers and non-carriers: MRSA infections fell 58% among patients who tested negative on admission, but only 31% among those who tested positive.
S. aureus infection rates among hospitalized patients, MRSA and MSSA, 2005–2017. Figure from the CDC report.
Hospital-onset bloodstream and nonbloodstream infection rates, 2005–2017. Figure from the CDC report.
Why it points to transmission
The authors weighed other explanations:
- Less testing? No — culture rates didn't change over the period, and didn't differ by MRSA carriage.
- A changing germ? National data show community-associated MRSA rates flat since 2005 while health care–associated rates fell, and almost all MRSA declines came from USA100, a strain tied to health care transmission, not USA300, a community strain.
- Device and surgery bundles? Those prevent colonized patients from becoming infected — and should have cut MRSA and MSSA about equally. They didn't.
Instead the evidence points to less MRSA transmission. Models predict that cutting transmission hits drug-resistant, hospital-adapted strains hardest; MRSA acquisition fell sharply; infections fell most among patients who weren't carriers on arrival; and early post-discharge infections dropped. Screening and contact precautions very plausibly contributed, along with measures that stop all germs spreading, such as hand hygiene. Less fluoroquinolone antibiotic use (down 44% in 2009–2017) might have helped, but it began only after MRSA had already fallen a great deal.
What it means
Recent calls to drop MRSA transmission measures such as contact precautions "might be premature and inadvisable," the authors conclude, at least until more is known about controlling germ transmission in health care. Preventing S. aureus takes a multifaceted approach: antibiotic stewardship, preventing device- and procedure-related infections, and stopping the spread of health care strains.
Limits: VA patients are mostly men; the models lacked data on adherence to infection control; there was no information on MSSA colonization or on strains; and simple trend models may not capture a complex system.
Sources
Based on Makoto Jones, John A. Jernigan, Martin E. Evans, Gary A. Roselle, Kelly M. Hatfield and Matthew H. Samore, "Vital Signs: Trends in Staphylococcus aureus Infections in Veterans Affairs Medical Centers — United States, 2005–2017," MMWR, Centers for Disease Control and Prevention; a work of the United States government in the public domain.
Licence: CC0 1.0 (public domain) · Adapted from www.cdc.gov
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