Cutting back on antibiotic courses in intensive care unit settings can significantly reduce the number of multidrug-resistant organism (MDRO) transmissions, according to the findings of a modeling study.

“Significant opportunities exist to optimize and reduce antibiotic usage, [but] the impact of reducing overall antibiotic usage on antibiotic resistance is not known and would be difficult to assess using traditional study designs,” wrote Sean L. Barnes, PhD, of the University of Maryland, College Park, and his colleagues. “Therefore, we applied mathematical modeling to estimate the effect of reducing antibiotic usage on antibiotic resistance.”

Using an agent-based model – which allows for a realistic prediction of interactions between patients and health care workers, while also allowing for heterogeneity in the characteristics of each distinct “person” – Dr. Barnes and his coinvestigators simulated the transmission of MDROs from health care workers to patients.

Methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci were deemed “high-prevalence pathogens;” carbapenem-resistant Enterobacteriaceae, multidrug-resistant Acinetobacter baumannii, and multidrug-resistant Pseudomonas aeruginosa were deemed low-prevalence pathogens. These designations were based on transmission rates found in existing literature.

Patients on antibiotic courses were set at 75% (0.75) at baseline, which was then adjusted to determine its effect on overall MDRO transmission. The number of patients at baseline was 18, with nine nurses, two physicians, and six other health care workers. Mean length-of-stay was 3.5 days, hand hygiene rates were set at 80% for nurses and 50% for physicians, with a 0.83 (83%) efficacy rate when followed. The probability of worker-to-patient transmission was set at 0.025 (2.5%), and set at 0.075 (7.5%) for transmission going the other way.

“We simulated the transmission of the high- and low-prevalence MDROs for 1 year [and] performed 200 replications each for 33 parameter-based scenarios,” the authors said.

When the number of patients on an antibiotic course was dropped from 75% to 65% (a drop of 10%), the rate of high-prevalence MDRO transmission dropped by 11.2% (P < .001). When reduced from 75% to 50% (a drop of 25%), the high-prevalence MDRO transmission rate fell by 28.3% (P < .001), according to the model.

Low-prevalence MDROs also reduced by significant amounts when antibiotic regimens were cut back by the same percentages, with transmission rates falling by 14.3% (P < .001) and 29.8% (P < .001), respectively.

In terms of microbiome effects, the 10% reduction in antibiotics lowered high-prevalence rates by an effect of 1.5, and low-prevalence rates by 1.7; those numbers were 1.2 and 1.4, respectively, when antibiotics were dropped by 25%.

“These reductions are statistically significant and proportionally similar for both high- and low-prevalence MDROs,” the authors concluded, “and they can potentially decrease MDRO acquisition among patients who are receiving antibiotics, as well as among patients who are not receiving antibiotics.”

The National Institutes of Health and the Department of Veterans Affairs’ Health Services Research and Development Department funded the study. Dr. Barnes and his coauthors reported no relevant financial disclosures.


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