Community-Associated Extended-Spectrum β-Lactamase–Producing Escherichia coli Infection in the United States

(See the Editorial Commentary by Foxman on pages 649–51.) Escherichia coli that produces extended-spectrum β-lactamase (ESBL) has become widespread in hospitals around the world since the late 1980s [1]. ESBLs refer to a group of β-lactamases that have acquired the capacity to hydrolyze penicillins, cephalosporins, and aztreonam [1, 2]. Organisms that produce ESBLs are thus resistant to most broad-spectrum β-lactams with the exception of carbapenems. The genes for these ESBLs are frequently encoded on transferable plasmids that also encode resistance genes for other classes of antimicrobials [3]. Acquisition of such plasmids can thus promptly render an organism multidrug-resistant [4]. In fact, it is commonly observed that ESBL-producing organisms are resistant to multiple classes of antimicrobials including β-lactams, fluoroquinolones, aminoglycosides, and sulfonamides [1]. The global spread of community-associated methicillin-resistant Staphylococcus aureus infections has emerged as a major public concern in recent years [5]. On the other hand, infections due to resistant gram-negative organisms have largely been regarded as a healthcare-associated phenomenon. However, emergence of community-associated infections caused by ESBL-producing E. coli has been reported in multiple countries since the mid-2000s [6–8]. In each of these instances, the ESBLs associated with community-associated infection have largely been the CTX-M type, specifically CTX-M-15, distinct from the TEM and SHV types that were historically common [2]. In addition, the majority of CTX-M–producing E. coli belong to a specific clone that is defined by phylogenetic group B2, serotype O25:H4, and multilocus sequence typing (MLST) profile ST131, including in the United States [9, 10]. However, the extent and significance of community-associated infections caused by ESBL-producing E. coli in the United States have not been elucidated. The potential spread of ESBL-producing E. coli in the community poses a public health concern as well as a challenge to the management of community-associated infections, which are typically treated empirically with agents such as oral cephalosporins or fluoroquinolones without antimicrobial susceptibility testing. The main objective of this study was to describe the occurrence of ESBL-producing E. coli in the community, and to assess the clinical outcome of these patients at multiple hospitals and their affiliated clinics across the United States. We also sought to identify additional risk factors associated with healthcare-associated ESBL-producing E. coli cases in comparison with community-associated cases.