Key Point

Risk of transmission of MRSA/VRE in the ICU is increased when prior occupants have acquired the bacteria.

BOSTON—Patients who stay in an ICU room previously occupied by a patient with methicillin-resistant Staphylococcus aureus (MRSA) or vancomycin-resistant enterococci (VRE) are at a significantly higher risk of acquiring the bacteria, according to a recent study.1 However, this increased risk is still a minor one, accounting for less than 10% of all cases of ICU bacteria infection, reported Susan S. Huang, MD, MPH, and colleagues.

Floors, beds, gowns, faucets, and other hospital room fixtures are persistently contaminated with MRSA and VRE, but it is not known whether levels of the bacteria are high enough to infect additional patients or whether currently mandated cleaning practices are effective in reducing the spread of bacteria. "Although high-risk rooms may exist because of difficult-to-clean design or poor placement of hand hygiene equipment, transmission may be more directly linked to a prior occupant who harbored a resistant organism rather than to a particular room," the researchers commented.

Huang et al assessed 10,151 ICU occupants at risk of acquiring MRSA and 10,349 ICU occupants liable to acquire VRE. An infection rate of 3.9% for MRSA was observed among patients whose prior room occupant had MRSA, compared with 2.9% of patients whose prior room occupant did not have the bacteria. Among patients whose prior room occupant had VRE, 4.5% acquired the bacteria, compared with 2.8% of patients whose prior room occupant did not have VRE. These differences in percentage represented a 40% increase in the risk of MRSA/VRE contamination associated with previous ICU room occupants.

However, the increased risk "accounted for 5.1% of all incident MRSA cases and 6.8% of all incident VRE cases, with a population attributable risk among exposed patients of less than 2% for either organism," noted Dr. Huang and colleagues. This finding "suggests that levels of contamination do not pose a high risk for transmission or that current cleaning methods generally reduce contamination below levels required for transmission."

Nevertheless, the investigators pointed out that the increased risk occurred despite adherence to hospital discharge cleaning procedures that exceeded the 2003 national guidelines of the Centers for Disease Control and Prevention and the Healthcare Infection Control Practices Advisory Committee. These added procedures included the replacement of privacy curtains and the use of pour bottles instead of spray bottles for cleaning, in order to prevent chemical agent aerosolization and to increase the quantity of cleaning agent used. Furthermore, Dr. Huang and colleagues added that "all environmental services aides underwent hands-on training in cleaning protocols, with twice-monthly quality control assessments in which compensation is tied to the mean scores for each fiscal year."

Despite the use of these precautionary cleaning measures that went beyond national guidelines, the researchers noted that their findings "strongly [suggest] a role for environmental contamination" and that "national recommendations for terminal room cleaning do not completely prevent transmission."

However, the "risk of transmission attributable to residual environmental contamination that persists despite terminal cleaning of patient rooms may not be applicable to heavily trafficked common areas, such as procedure rooms, hallways, physician work areas, and nursing stations," the investigators pointed out. While bacteria transmission may result from direct patient contact with the environment, contamination in heavily trafficked common areas might instead be caused by medical staff serving as intermediary carriers.

"The effect of current cleaning practices in reducing the risk to the observed levels and the potential for further reduction are unknown," Dr. Huang’s research team concluded. "Additional data are needed to determine whether more intensive cleaning practices can reduce the risk further and, if so, whether this is worthwhile in a resource-limited system."

—John Merriman

Reference
1. Huang SS, Datta R, Platt R. Risk of acquiring antibiotic-resistant bacteria from prior room occupants. Arch Intern Med. 2006;166:1945-1951.