Environmental Contamination as a Potential Source of MRSA Transmission

Ehsanollah Ghaznavi-Rad, MSc, of the Department of Medical Microbiology and Parasitology at the Universiti Putra Malaysia, and colleagues, report in a research brief in Infection Control & Hospital Epidemiology on a study they conducted to trace the source of nosocomial transmission of methicillin-resistant Staphylococcus aureus (MRSA) by investigating the impact of healthcare workers and the hospital environment. They assessed the prevalence and the molecular characteristics of MRSA strains isolated from the study sources and compared these with clinical isolates obtained previously.

The researchers report that 500 samples consisting of 40 environmental specimens and 460 nasal swab specimens were collected from the wards with the highest rates of MRSA colonization and infection. Of the 460 healthcare workers, 94 were nasally colonized with S. aureus; of the 40 environmental samples, four were positive for MRSA.

The researchers note that MRSA nasal carriage of MRSA among healthcare workers at the study hospital was not a significant source of infection due to routine healthcare worker screening and ambitious hand hygiene practices. They do emphasize that the hospital environment seems to pose a threat for nosocomial transmission, and say that S. aureus is able to survive for months in a relatively hostile environment, thus potentially representing environmental reservoirs of MRSA. The researchers point to the seminal review by Dancer in 2008 that highlighted the importance of the hospital environment for MRSA transmission, and that removal of debris that helps support microbial growth can help control this transmission. The researchers caution however, Although the hospital environment was identified as a possible source of nosocomial MRSA transmission, healthcare worker could not be excluded as a clinically relevant source, because healthcare workers still carried strains with significant numbers of virulence genes.

Reference: Ghaznavi-Rad E, et al. Environmental Contamination in the Hospital as a Possible Source for Nosocomial Infection with Methicillin Resistant Staphylococcus aureus. Infect Control Hosp Epidem. 31:12;1302-1303. December 2010.