Clinical Relevance

Infections in long-term care facilities (LTCFs) represent a major cause of morbidity and mortality in the elderly (1-3). Because of this increased infection rate, antimicrobials are among the most frequently prescribed medications (4). Studies have shown that antibiotics account for nearly 40% of all systemic drugs used in LTCFs (5). In this unique environment, the most challenging questions facing the geriatrician are not which antibiotics are available that can treat the suspected infection, but which are the most appropriate to use.

Although antibiotics are necessary to treat infections in the elderly, their use may be excessive (6). In a study performed by Zimmer and colleagues (7), in 37.6% of cases, the evidence to start an antibiotic was considered inadequate. Of all antibiotic classes, cephalosporins were the most frequently overused (8). As a result of frequent antibiotic use in LTCFs, we are now challenged with the problem of increasing antimicrobial resistance (9). Nearly 10 years ago, it was articulated that LTCFs would become the reservoir for the evolution of antibiotic resistant genes (10). At that time, attention centered on methicillin resistance in staphylococci and third-generation cephalosporin resistance in enteric bacilli. Trimethoprim/sulfamethoxazole (TMP/SMX) resistance and aminoglycoside resistance in Gram-negative bacteria were recognized as significant problems for nearly 20 years (11,12). Geriatricians are now facing the fear of treating multiresistant organisms in a population that is relatively immunocompromised (13-16). In many ways, the activities and practices in LTCFs are ideal for the emergence of resistant bacteria.

Bacteria possessing antibiotic resistance determinants arise in LTCFs by one of two ways. The transfer of infected or colonized patients from hospital to LTCF is believed to be the primary way resistant bacteria are introduced into nursing facilities (nursing homes). A contemporary example of this is the spread of methicillin-resistant Staphylococcus aureus (MRSA) to LTCFs from tertiary care centers (17). In this study, a single asymptomatic carrier passed MRSA to 24 veterans in a skilled care unit. Second, the excessive and inappropriate use of antibiotics can select for mutations in bacterial gene(s) that confer a selective advantage. Examples of this are (1) the selection of mutations in ^-lactamase genes that confer resistance to third-generation cephalospor-

From: Infectious Disease in the Aging Edited by: Thomas T. Yoshikawa and Dean C. Norman © Humana Press Inc., Totowa, NJ

ins (18,19), (2) the selection of quinolone-resistant bacteria with mutations in gyrA and gyrB or parC (20,21), and (3) mutations in dhfr, which confer resistance to TMP/SMX (22). Once endemic to an LTCF, the antibiotic resistance genes can be transferred from one patient to another and from one species or genus to another (23).

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