News in Antimicrobial Resistance: Documenting the Progress of Pathogens

Antimicrobial resistance is expensive and deadly, and consumes an increasing proportion of infection control practitioners’ time. In 2003, four of 12 issues of Infection Control and Hospital Epidemiology were almost entirely devoted to questions surrounding antibiotic resistance and all but one of the issues of the Journal of Hospital Infection contained articles about the problem. As reflected in this month’s issue of Infection Control and Hospital Epidemiology,1-5 most attention is being paid to resistance in the two gram-positive pathogens that are the most common cause of hospital-acquired infections—Staphylococcus aureus and enterococci. However, we can expect to see increasing numbers of publications documenting the emergence of clinically significant resistance in the two other common nosocomial pathogens—Escherichia coli and Klebsiella species. Articles in this issue of Infection Control and Hospital Epidemiology document two important new problems with antimicrobial resistance. Warren et al. and Harris et al. provide quantitation of the strong associations between colonization with methicillin-resistant S. aureus (MRSA) and vancomycin-resistant enterococci (VRE), and VRE and extended-spectrum beta-lactamase–producing E. coli and Klebsiella. They note that risk factors for acquiring antibiotic-resistant organisms, including severity of underlying illness, duration of hospital stay, colonization pressure, and antimicrobial use, are common for all antibiotic-resistant pathogens. Our most vulnerable patients are most likely to be infected with resistant pathogens, and most likely to suffer in consequence. In addition, as noted by Warren et al., co-colonization with MRSA and VRE indubitably increases the risk of the emergence of vancomycin-resistant S. aureus. To date, this has rarely occurred.6 However, the continuing increase in MRSA and VRE co-colonization will inevitably lead to further episodes of transfer. It is clear that the increasing prevalence of MRSA and VRE in healthcare institutions is primarily related to transmission of strains from patient to patient, with antibiotic pressure providing an important facilitative role.7 In contrast, antibiotic resistance in E. coli and Klebsiella species has often been viewed as a result of the overuse of antibiotics, rather than a consequence of the transmission of strains (or plasmids) within hospitals. The documentation by Harris et al. of the very high association between colonization with VRE and extended-spectrum beta-lactamase–producing bacteria suggests that transmission may be a greater problem than is commonly thought. Recently, a careful examination of the issue by Paterson et al.8 arrived at the conclusion that patient-to-patient transmission in the hospital is critically important in the emergence of antibiotic resistance in Klebsiella species. Warren et al., Eveillard et al., and Leman et al. document another problem with hospital-derived antimicrobialresistant organisms—not only are they often transferred to long-term–care facilities, they may also cause problems in the community. Warren et al. noted that patients co-colonized with MRSA and VRE were more likely to be transferred to long-term–care facilities than were other patients. Eveillard et al., in a carefully designed study of employees in a hospital in France with endemic MRSA, documented not only infections in healthcare workers, but also substantial MRSA transmission in the households of colonized healthcare workers. Leman et al. found that 2.1% of an American Indian population was colonized with MRSA. Forty-four percent of the MRSA colonization occurred in individuals with healthcare risk factors. The recent emergence of true community-acquired MRSA in many parts of the world may make control of MRSA in hospitals more challenging. However, in most cases, what appears to be community-acquired MRSA is often actually healthcare-acquired MRSA.9 The article by Leman et al. provides another important insight into the problem of MRSA control. During an outbreak of community-onset MRSA infections in an American Indian community in which 34% of all S. aureus