Impact of stopping contact precautions on vanA plasmid transmission, Northern California, 2021-2023

To evaluate the impact of discontinuing contact precautions for vancomycin-resistant enterococci (VRE) on strain and plasmid transmission using long-read whole-genome sequencing (WGS).

Before-after trial of adults with Enterococcus bloodstream infections pre-(Jan-Oct 2021) and post-(Oct-Dec 2021 and Jan-Oct 2023) discontinuation of contact precautions for VRE infections.

Quaternary referral and transplant academic medical center.

Hospitalized adults (≥18 yr) with E. faecalis or E. faecium bacteremia.

Classical epidemiology identified potential transmissions via shared unit exposure within a 14-day window. Blood culture isolates underwent long-read WGS to assess strain and vanA plasmid relatedness. Clonal transmission was defined as <20 single-nucleotide polymorphisms. Plasmid similarity was assessed with Mash distance.

Among 288 isolates from 202 patients, there was no significant difference in possible epidemiologic transmissions pre-versus postdiscontinuation (9.5% vs 8.1%; P = .679). Genomic analysis identified four clonal transmission events, two of which occurred postdiscontinuation. Among 70 vanA plasmids from 54 patients, 38 highly related plasmids formed a low-diversity cluster. The proportion of cluster plasmids was not significantly different between periods (47% vs 60%; P = .267). Postdiscontinuation, vanA-positive E. faecium ST117 was more prevalent (22/44 vs 53/75; P = .024).

Discontinuation of contact precautions for VRE was not associated with increased transmission of enterococci or vanA plasmids in bloodstream infections. Transmission patterns remained largely stable, though the postdiscontinuation period showed increased prevalence of the dominant E. faecium ST117. These findings suggest limited impact of contact precautions on VRE transmission.