Understanding short-term transmission dynamics of methicillin-resistant Staphylococcus aureus in the patient room

Abstract

Objective: Little is known about the short-term dynamics of methicillin-resistant Staphylococcus aureus (MRSA) transmission between patients and their immediate environment. We conducted a real-life microbiological evaluation of environmental MRSA contamination in hospital rooms in relation to recent patient activity.

Design: Observational pilot study.

Setting: Two hospitals, hospital 1 in Zurich, Switzerland, and hospital 2 in Ann Arbor, Michigan, United States.

Patients: Inpatients with MRSA colonization or infection.

Methods: At baseline, the groin, axilla, nares, dominant hands of 10 patients and 6 environmental high-touch surfaces in their rooms were sampled. Cultures were then taken of the patient hand and high-touch surfaces 3 more times at 90-minute intervals. After each swabbing, patients' hands and surfaces were disinfected. Patient activity was assessed by interviews at hospital 1 and analysis of video footage at hospital 2. A contamination pressure score was created by multiplying the number of colonized body sites with the activity level of the patient.

Results: In total, 10 patients colonized and/or infected with MRSA were enrolled; 40 hand samples and 240 environmental samples were collected. At baseline, 30% of hands and 20% of high-touch surfaces yielded MRSA. At follow-up intervals, 8 (27%) of 30 patient hands, and 10 (6%) of 180 of environmental sites were positive. Activity of the patient explained 7 of 10 environmental contaminations. Patients with higher contamination pressure score showed a trend toward higher environmental contamination.

Conclusion: Environmental MRSA contamination in patient rooms was highly dynamic and was likely driven by the patient's MRSA body colonization pattern and the patient activity.

Fig. 1.

Proportion of MRSA-positive patient hands, environment, and air. Icons represent tested sites, in the center the patient’s dominant hand, in the outer circle the environmental sites: clockwise beginning at 10 o’clock: bed remote control, bathroom inside door handle, toilet seat, bedside table (each for hospital 1 and 2), bed rail and patient room inside door handle (for hospital 1 only), television remote control and room phone (for hospital 2 only), in figure B at the bottom room air. The surface of grey disks are sized proportionately to contamination prevalence of sites, exact prevalence is depicted as a number above.

Fig. 2.

Patient colonization status, hand and environmental contamination, and “contamination pressure” score. Manikin: Patient infected (INF +) or colonized (COL +) with MRSA, shaded circles represent MRSA positive sample sites of nose, axilla and groin (dark grey circles are positive direct cultures, light gray circles are positive enrichment cultures). Drop: Chlorhexidine body wash. Activity: Semiquantification of activity from 1 (ie, very inactive) to 4 (ie, very active). Contamination pressure score: Product of activity score × number of colonized body sites. Items: Sample sites, from upper-left to lower-right corner for hospital 1: patient hand, air, door handle patient room, remote control bed, bed rail, toilet seat, bedside table, door handle bathroom; for hospital 2: patient hand, TV remote control, bed remote control, room phone, toilet seat, bedside table, door handle bathroom; circles represent MRSA-positive sample sites. Grey-colored circles are positive cultures, framed circles are positive enrichment cultures. Patient activities: Description of patient activities during 90-minute episodes; No. of people in room (HCW/non-HCW).

Fig. 3.

Correlation of contamination pressure score with environmental contamination. The contamination pressure score was calculated by multiplication of “activity level” with the number of colonized body sites (0–3, of axilla, groin, nares). Activity level was defined by quantification of the patient activity (from 1 to 4, with 1 “very inactive,” 2 “inactive,” 3 “active,” and 4 “very active”). Number of contaminated environmental sites are total number of all 3×6 swabbed sites of follow-up 1 to follow-up 3 (ie, theoretical maximum of 18 sites). The odds ratio of the ordered logistic regression analysis is included in the figure.