Diversity and persistence of MRSA and VRE in skilled nursing facilities: environmental screening, whole-genome sequencing and development of a dispersion index.

BACKGROUND: Environmental contamination with meticillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) in skilled nursing facilities (SNFs) may contribute to patient acquisition. This study assessed diversity and association of MRSA and VRE isolates in an SNF wing, and developed a mathematical index to define the tendency of each strain to persist in rooms and spread horizontally. METHODS: This was a longitudinal study of MRSA and VRE colonization and contamination among successive patient occupancies in a cluster of nine SNF private rooms over 8 months, characterized by microbiological testing and whole-genome isolate typing. The 'dispersion index' of a strain was defined as the number of rooms in which it was found (including if it was found in the patient), divided by the average number of times it was found consecutively in the same room. FINDINGS: MRSA (10 strain types) and VRE (seven types) were recovered from the room or patient in 16.4% and 35.6% of the occupancies, respectively. MRSA showed moderate horizontal spread and several episodes of same-room persistence (three distinct strain types) (overall dispersion index 1.08). VRE showed a high tendency towards horizontal spread/new introductions (overall dispersion index 3.25) and only one confirmed episode of persistence. INTERPRETATION: The emerging picture of high diversity among contaminating strains and high likelihood of room persistence despite terminal cleaning (MRSA) and horizontal spread between rooms (VRE) in this setting calls for improved cleaning practices, heightened contact precautions and, most of all, establishment of individually tailored facility screening programmes to enable informed choices based on local, measurable and actionable epidemiologic parameters.

Infection rate and colonization with antibiotic-resistant organisms in skilled nursing facility residents with indwelling devices.

The objective of this prospective surveillance study was to quantify colonization with antimicrobial-resistant organisms (AROs) and infections attributable to indwelling devices in skilled nursing facility (SNF) residents. The study was conducted in 15 SNFs in Southeast Michigan. Residents with (n=90) and without (n=88) an indwelling device were enrolled and followed for 907 resident-months. Residents were cultured monthly from multiple anatomic sites and data on infections were obtained. The device-attributable rate was calculated by subtracting the infection rate in the device group from the infection rate in the non-device group. A total of 197 new infections occurred during the study period; 87 in the device group (incidence rate [IR] =331/1,000 resident-months) and 110 infections in the non-device group (IR=171/1,000 resident-months), with a relative risk of 1.9 (95% confidence interval [CI]: 1.4-2.6). The attributable rate of excess infections among residents in the device group was 160/1,000 resident-months, with an attributable fraction of 48% (95% CI: 31-61%). Prevalence rates for all AROs were higher in the device group compared with the no-device group. The prevalence of the number of AROs per 1,000 residents cultured increased from no-device to those with only feeding tubes, followed by those with only urinary catheters and both these devices. In conclusion, the presence of indwelling devices is associated with higher incidence rates for infections and prevalence rates for AROs. Our study quantifies this risk and shows that approximately half of all infections in SNF residents with indwelling devices can be eliminated with device removal. Effective strategies to reduce infections and AROs in these residents are warranted.