How important is the environment in the emergence of nosocomial antimicrobial-resistant bacteria?

Antimicrobial-resistant bacteria are an emerging problem globally and are associated with increased patient morbidity and mortality. Within hospitals, antibiotic resistant bacteria continue to increase in incidence. As evidenced by the Centers for Disease Control and Prevention National Healthcare Safety Network collection of data across a large number of hospitals, resistance rates for vancomycin-resistant enterococci (VRE), methicillin-resistant Staphylococcus aureus, imipenem-resistant Pseudomonas aeruginosa, and cephalosporin-resistant Escherichia coli and Klebsiella species continue to increase [1]. These increases in antibiotic-resistant bacteria continue to occur despite efforts to contain them by numerous parties, including the Centers for Disease Control and Prevention, Veterans Health Administration , public interest groups, quality improvement administrators, antimicro-bial stewardship teams, and hospital epidemiologists. Figure 1 is a theoretical model that demonstrates a number of potential causal variables leading to the acquisition of antibiotic resistant bacteria by patients [2]. These causal variables are divided into individual level factors and facility-level factors. The relative importance of causal variables , such as antibiotic selective pressure and patient–to-patient transmission, are not definitely known for most antibiotic-resistant bacteria. In addition, their relative importance likely differs for different antibiotic-resistant bacterial species [3, 4]. For organisms such as methicillin-resistant S. aureus, VRE, and extended-spectrum b–lactamase–producing bacteria, patient–to-patient transmission via health care workers' hands is thought to be an important cause of the increasing incidence of these antibiotic-resistant bacteria [4–6]. However, the role of environmental contamination in contributing to patient– to-patient transmission is a hotly disputed topic [7, 8]. Numerous studies have demonstrated that the environment of a patient's room can become colonized with bacteria, such as Acinetobacter species, VRE, Clostridium difficile, and methicillin-resistant S. aureus, as well as with viruses, such as influenza virus and norovirus [8]. But the importance of this colonization in leading to patient–to-patient transmission has not been shown with a high level of scientific evidence. Problems with previous studies have included the following: (1) many were performed in an outbreak setting; (2) when environmental intervention studies have been done, they often have been of a lower-level quasi-experimental study design [9]; and (3) few studies have used molecular epidemiology (e.g., PFGE) to link environmental isolates to patient isolates. Recently, a couple of methodologi-cally improved studies found that the environment may be important in the hospital acquisition of VRE. A study by Huang et al. [10] demonstrated that patients admitted to rooms that had previously been occupied by VRE-positive patients were more likely to acquire VRE. …