Molecular Characterization of the Transmission between the Colonization of Methicillin-resistant Staphylococcus aureus to Human and Environmental Contamination in Geriatric Long-term Care Wards

Objective Transmission between human and environmental contamination from colonized methicillin-resistant Staphylococcus aureus (MRSA) remains a controversial issue. We, therefore, investigated the differences between MRSA types which colonize in humans and in the environment. Methods A 4-week prospective culture survey for MRSA was performed for 12 patients as well as for the environment of the room of MRSA carriers in quarantine in the geriatric long-term care ward of a 270-bed hospital. Results A total of 97 S. aureus strains (80 MRSA and 17 methicillin-sensitive Staphylococcus aureus [MSSA]) was isolated during the periods of September 8 to 10, 23 to 25 and October 5 to 7, 1998; 25 strains were from the respiratory tract, 4 strains from feces and 11 strains from decubitus ulcers. Fifty-seven strains were from the patients' environment. Molecular typing by pulsed-field gel electrophoresis (PFGE) with the Sma I restriction enzyme demonstrated that the predominant type of MRSA isolated from the environment changed by the minute. The patterns of 42 MRSA strains isolated from the environment were identical in 26 (61.9%), closely related in 15 (35.7%) and possibly related in 1 (2.4%) of the cases of those isolated from patients simultaneously. There was no correlation between patients and the environment with the 17 MSSA isolates. Conclusion Our results demonstrated that MRSA from patients can contaminate the environment, whereas MRSA from the environment might be potentially transmitted to patients via health care workers under unsatisfactory infection control