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MRSA likely to persist in nursing homes; large-scale outbreaks doubtful
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MRSA is unlikely to be eradicated from nursing home settings, but large-scale outbreaks also are unlikely, according to a modeling study published in Antimicrobial Resistance and Infection Control.
“Elimination of MRSA introductions could theoretically be achieved through active surveillance, particularly when coupled with effective social distancing interventions or decolonization therapy,” Nataliya G. Batina, MS, doctoral student with the department of industrial and systems engineering at the University of Wisconsin-Madison, and colleagues wrote. “Nevertheless, the likelihood of achieving these outcomes in actual practice seems remote for a variety of reasons.”
MRSA is common among residents of nursing homes, but the circumstances that lead to its spread in this setting are not well-understood, the researchers said. Thus, Batina and colleagues used mathematical modeling to assess the epidemic potential of MRSA in nursing homes and identify ways that community-associated strains of the bacteria, specifically non-USA300 and USA300, could be eliminated or reduced.
The researchers developed deterministic and stochastic co-colonization and single-strain models to describe transmission dynamics of MRSA in the facilities. Model inputs were derived from data on 446 patients with MRSA collected during a longitudinal study of antibiotic resistance in six nursing homes in Wisconsin. The data included residents’ colonization status with strain-specific MRSA collected every 3 months for up to 1 year. Batina and colleagues estimated reproduction numbers of strain-independent MRSA, non-USA300 and USA300 MRSA and evaluated the impact of antibiotic use on the prevalence of strain-specific MRSA.
The models predicted that, under the observed conditions, MRSA would remain endemic in the long run, with non-USA300 continuing to be the dominant strain. After 20 years, 11% of residents were predicted to be colonized with non-USA300, 1.5% with USA300, and less than 1% colonized with both MRSA strains.
This digitally colorized scanning electron micrograph of MRSA bacteria.
Source: NFID
The basic reproduction number of strain-independent MRSA was 0.18 (95% CI, 0.13-0.23). Antibiotic use in the past 3 months was associated with nonsignificant increases in the prevalence of strain-specific MRSA. Notably, the elimination of intra-facility cross-transmission was shown to have minimal impact on the predicted rates of MRSA.
According to the models, eradication of MRSA from nursing homes would require eliminating all MRSA-positive admissions or selectively discharging colonized residents, both conditions that the researchers deemed highly unlikely.
“Our findings suggest that MRSA elimination in nursing homes is unlikely but reductions in the prevalence of MRSA are theoretically achievable, particularly through interventions that accelerate the rate of resident de-colonization or reduce the admission prevalence of MRSA,” the investigators wrote. “Nevertheless, our models predict that these interventions would need to be sustained over a period of years in order to have a demonstrable effect on observed patterns of colonization. – by Sarah Kennedy
Disclosure: The researchers report no relevant financial disclosures.
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