Antibiotic Consumption Impacts Horizontal VRE Transmission

In an in-press article in the journal Diagnostic Microbiology and Infectious Disease, Elise M. Gilbert, Pharm D, from Midwestern University Chicago College of Pharmacy, and colleagues highlight correlations between antibiotic use and horizontal transmission of Vancomycin-resistant Enterococcus (VRE) bacterial species.

According to the authors, aztreonam therapy was associated with a lower rate of VRE transmission events in the medical intensive care unit, while carbapenem therapy was associated with a higher rate of transmissions on one of two oncology units.

Vancomycin-resistant Enterococcus (VRE) is a strain of Enterococcus that has become resistant to vancomycin, an antibiotic that is commonly used in hospitals. These bacteria pose a significant public health threat, especially because patients infected with or colonized by VRE experience increased mortality, longer hospital stays, and greater healthcare costs than patients without VRE do.

Increasing antimicrobial use has been shown to promote antimicrobial resistance, particularly among clinical bacterial isolates. However, data are lacking on the effect of antibiotic use on hospital-based transmission of resistant bacteria.

“We were interested [in learning] if antibiotic consumption had any impact on VRE transmission events,” the study’s corresponding author, Marc H. Scheetz, PharmD, MSc, also from Midwestern University Chicago College of Pharmacy, told Contagion^®. “When we reviewed the literature, we were unable to find any information about this potential relationship.”

The researchers therefore designed a study to examine the association between antimicrobial use, hand hygiene, and horizontal transmission of resistant bacteria.

“We identified a signal that antibiotic consumption may impact the horizontal transfer of VRE,” said Dr. Scheetz. “This is one more important reason to use antibiotics judiciously.”

However, although poor hand hygiene is one of the most important factors in horizontal transmission of bacteria in hospitals, the researchers found no direct link between antimicrobial use and breaches in hand hygiene. Hand hygiene rates were high in this study, they say, with no rate reported as less than 70%.

Dr. Scheetz noted that, although additional research is needed in this area, the findings of this study further suggest that antibiotic use may have currently undocumented negative effects. “We postulate that high antibiotic use may ‘prime’ an environment for transmission of antibiotic-resistant organisms,” he stressed. “These data provide one more reason to appropriately steward our precious antibiotic resources.”

Emphasizing his group’s interest in the trends of antibiotic consumption and associated downstream events, Dr. Scheetz also discussed additional studies in the pipeline to identify signatures of inappropriate antibiotic use from antibiotic consumption data. “As a backdrop for these studies, we have been attempting to understand how antibiotic use trends over time,” he said.

Referring to recent work by his group, Dr. Scheetz focused on a supplementary file that is available for free download. This is an electronic translation of a statistical methodology to trend antibiotic use in Microsoft Excel, he said.

By using this file, investigators “can identify linear trends in antibiotic use and utilize prediction intervals to help determine if use is higher or lower than expected,” he concluded.

Dr. Parry graduated from the University of Liverpool, England in 1997 and is a board-certified veterinary pathologist. After 13 years working in academia, she founded Midwest Veterinary Pathology, LLC where she now works as a private consultant. She is passionate about veterinary education and serves on the Indiana Veterinary Medical Association’s Continuing Education Committee. She regularly writes continuing education articles for veterinary organizations and journals, and has also served on the American College of Veterinary Pathologists’ Examination Committee and Education Committee.