AIR AND SURFACE CONTAMINATION PATTERNS OF METHICILLIN-RESISTANT Staphylococcus aureus ON EIGHT ACUTE HOSPITAL WARDS

Abstract

BACKGROUND. Methicillin-resistant Staphylococcus aureus (MRSA) can be recovered from hospital air and from environmental surfaces. This poses a potential risk of transmission to patients. OBJECTIVE. To investigate associations between MRSA isolates recovered from air and environmental surfaces with those from patients when undertaking extensive patient and environmental screening. DESIGN. A prospective observational study of patients and their environment in eight wards of a 700-bed tertiary care hospital during 2010 and 2011. METHODS. Sampling of patients, air and surfaces was carried out on all ward bays, with more extended environmental sampling in ward high-dependency bays (HDBs) and at particular times of the day. The genetic relatedness of isolates was determined by DNA microarray profiling and spa typing. RESULTS. MRSA was recovered from 30/706 (4.3%) patients and from 19/132 (14.4%) air samples. On 9/132 (6.8%) occasions both patient and air samples yielded MRSA. In 32 HDBs, MRSA was recovered from 12/161 (7.4%) patients, 8/32 (25%) air samples, and 21/644 (3.3%) environmental surface samples. On 10/132 (7.6%) occasions, MRSA was isolated from air in the absence of MRSA-positive patients. Patient demographic data combined with spa typing and DNA microarray profiling revealed four transmission clusters, where patient and environmental isolates were indistinguishable or deemed to be very closely related.