Colonization of patients and contamination of the patients’ environment by MRSA under conditions of single-room isolation

Meticillin-resistant Staphylococcus aureus (MRSA) are endemic in hospitals worldwide and present a major concern in hospital hygiene. The aim of the present study was to investigate the relationship between patients’ MRSA colonization of the body and the frequency of environmental contamination.Twenty-five MRSA-positive hospitalized surgical patients and their environment in isolation rooms were screened on four occasions over a 14-day period.Out of 1099 samples from patients, 330 (30.0%) were MRSA-positive. The median number of MRSA-positive body sites per screening decreased significantly from the 1st (3, range 1–9) to the 14th (2, range 0–9, p=0.011) day of isolation. Contamination was found in 45% of the 100 environmental sampling dates and MRSA was detected in a low proportion of the 1000 environmental surface samples: 105/1000 (10.5%). The number of positive results for each sampling date decreased from the 1st (median 1, range 0–8) to the 14th (median 0, range 0–3, p=0.21) day of isolation.The results show a very strong correlation between the number of MRSA-positive body sites of individual patients and the MRSA contamination of the patient's hospital room (r=0.700, p<0.001). Pulsed-field gel electrophoresis (PFGE) analysis demonstrated a 98% agreement between patient and environmental samples.MRSA colonization of the groin area correlates most strongly with colonization of the body and environment. Seventy-five of 240 (31%) samples taken in rooms of patients with colonization of the groin were MRSA-positive, whereas only 27 of 760 (3.6%) samples taken in rooms of patients without colonization of the groin produced positive results (odds ratio 12.3; 95% confidence interval, 7.7–20).It is concluded that MRSA patients without colonization of the groin have a relatively low risk of environmental spread of MRSA and thus a reduced risk of transmission.