There are an estimated 150 million urinary tract infections per annum worldwide (26). In the United States, urinary tract infections result in approximately 8 million physician visits per year (30). Urinary tract infections are the most common bacterial infections in women and account for significant morbidity and health care costs (4, 26). A limited and predictable spectrum of organisms cause urinary tract infections in young, otherwise healthy females. Among both outpatients and inpatients, Escherichia coli is the primary urinary tract pathogen, accounting for 75 to 90% of uncomplicated urinary tract infection isolates (4, 21). Staphylococcus saprophyticus, Klebsiella spp., Proteus spp., Enterococcus spp., and Enterobacter spp. are pathogens less commonly isolated from outpatients.The currently recommended empirical antimicrobial regimen for treating acute uncomplicated bacterial cystitis in otherwise healthy adult nonpregnant females is a 3-day course of double-strength trimethoprim-sulfamethoxazole (SXT) in settings where the prevalence of SXT resistance is Ͻ10 to 20% (1, 30). Investigators studying the economic impact of SXT and ciprofloxacin therapies have presented data supporting the empirical use of SXT when the local rate of resistance to SXT does not exceed 22% (14). Alternative therapy for uncomplicated urinary tract infections in settings with Ͼ10 to 20% SXT resistance may include a fluoroquinolone, nitrofurantoin, or fosfomycin (30).The Infectious Diseases Society of America also recommends that physicians obtain information on local resistance rates and that ongoing surveillance be conducted to monitor changes in susceptibility of uropathogens (30). Surveillance at the institutional and regional level is particularly important given that previous studies have reported that the activity of SXT against urinary isolates of E. coli can vary considerably by geographic region (6,25). The prevalence of SXT resistance among urinary pathogens appears considerable in the United States, and it seems inevitable that SXT will eventually need to be replaced by alternative therapies, at least in some areas (5-7, 11, 26).In vitro studies specifically describing the antimicrobial susceptibilities of urinary isolates of E. coli from female outpatients are limited (5-7, 9, 12, 18). In these studies, SXT resistance increased from 7 to 9% in 1989 to 1992 (5, 7, 18, 28) to 17 to 18% in 1995 to 1999 (5-7, 12). Fluoroquinolone resistance was Յ1% in each of the aforementioned studies, and nitrofurantoin resistance was reported to be Յ2% on national and regional levels in the United States. The 1998 SENTRY surveillance program, reporting on isolates of E. coli collected from 26 U.S. centers, found the overall prevalence of SXT

The ongoing TRUST (Tracking Resistance in the United States Today) study, which began monitoring antimicrobial resistance among respiratory pathogens in 1996, routinely tracks resistance at national and regional levels. The 1999-2000 TRUST study analyzed 9499 Streptococcus pneumoniae, 1934 Haemophilus influenzae, and 1108 Moraxella catarrhalis isolates that were prospectively collected from 239 laboratories across the 9 US Bureau of the Census regions. Penicillin-resistant S. pneumoniae varied significantly by region, from 8.3% to 24.8% (P<.001). In each region, penicillin resistance closely predicted resistance to other beta-lactams, macrolides, and trimethoprim-sulfamethoxazole. Levofloxacin resistance was 0.5% nationally (regional range, 0.1%-1.0%). Multidrug resistance also varied significantly (P<.001) by region. beta-Lactamase production among H. influenzae varied significantly (regional range, 24.0%-34.6%) and M. catarrhalis (86.2%-96.8%) also varied by region. Notable variation in regional antimicrobial resistance rates (S. pneumoniae) and beta-lactamase production (H. influenzae, M. catarrhalis) exists throughout the United States.

Although changing patterns in antimicrobial resistance in Streptococcus pneumoniae have prompted several surveillance initiatives in recent years, the frequency with which these studies are needed has not been addressed. To approach this issue, the extent to which resistance patterns change over a 1-year period was examined. In this study we analyzed S. pneumoniae antimicrobial susceptibility results produced in our laboratory with isolates obtained over 2 consecutive years (1997-1998 and 1998-1999) from the same 96 institutions distributed throughout the United States. Comparison of results revealed increases in resistant percentages for all antimicrobial agents studied except vancomycin. For four of the agents tested (penicillin, cefuroxime, trimethoprim-sulfamethoxazole, and levofloxacin), the increases were statistically significant (P < 0.05). Resistance to the fluoroquinolone remained low in both years (0.1 and 0.6%, respectively); in contrast, resistance to macrolides was consistently greater than 20%, and resistance to trimethoprim-sulfamethoxazole increased from 13.3 to 27.3%. Multidrug resistance, concurrent resistance to three or more antimicrobials of different chemical classes, also increased significantly between years, from 5.9 to 11%. The most prevalent phenotype was resistance to penicillin, azithromycin (representative macrolide), and trimethoprim-sulfamethoxazole. Multidrug-resistant phenotypes that included fluoroquinolone resistance were uncommon; however, two phenotypes that included fluoroquinolone resistance not found in 1997-1998 were encountered in 1998-1999. This longitudinal surveillance study of resistance in S. pneumoniae revealed that significant changes do occur in just a single year and supports the need for surveillance at least on an annual basis, if not continuously.Resistance to ␤-lactams, macrolides, and trimethoprim-sulfamethoxazole (SXT) continues to increase among clinical isolates of Streptococcus pneumoniae. This trend, coupled with the potential for increasing resistance to fluoroquinolones, has prompted several surveillance studies in recent years (4-6, 10, 17, 22, 23). Although evolving patterns in antimicrobial resistance suggest clearly an exigency for such surveillance initiatives, the frequency with which studies are needed has not been addressed.The decision to expend resources to perform resistance surveillance must be based on a careful assessment of how frequently the data and information are needed. One approach to making this determination involves establishing the extent to which resistance rates and patterns change over a given time period. Among the surveillance reports published in recent years, there are substantial differences among institutions, geographic regions, and countries represented; the number of institutions involved; and the time periods during which the isolates were obtained (5,6,10,17,21,22). These differences make analysis of resistance change over time difficult, and only rarely have studies addressed the extent of changes in resista...

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