By Ansbach, Robert K; Dybus, Karen; Bergeson, Rachel
Abstract.
Treatment of uncomplicated urinary tract infections (UTIs) has changed in the past few years with researchers advocating empiric treatment for shorter periods of time without the use of cultures. Researchers report that antibiotic resistance of Escherichia coli (E coli) to commonly prescribed antibiotics in uncomplicated UTIs has been increasing. Trimethoprim/sulfamethoxazole (TMP/SMX) is 1 of these antibiotics. Researchers also report that resistance patterns may differ depending on the geographic area of the United States. In this study, the authors present the results of a 7-month retrospective chart analysis of 98 E coli sensitivities to commonly prescribed antibiotics in the treatment of uncomplicated UTIs at a college health service. They examined the more common antibiotic choices and analyzed their in vitro responses. Of these antibiotics, ciprofloxacin, nitrofurantoin, amoxicillin/clavulanate, and TMP/SMX had the highest sensitivity rates. The authors compared the results with a previous study that they performed at the same institution in 1993. The results of this study show a sensitivity rate of 86% for TMP/SMX. When compared with the previous result of 87%, this represented a 1% change. Because of this slight decrease in sensitivity and the increasing concern over resistance, the authors suggest that they will continue to reevaluate the resistance pattern in their population on a regular basis. This will help determine if there is a need for modifying choices of empiric therapy for UTIs.
Key Words: antibiotics, bacterial resistance, E coli, trimethoprim/sulfamethoxazole, urinary tract infections
Escherichia coli (E coli) still remains the most common causative pathogen in uncomplicated urinary tract infection (UTI). It is the predominant organism in approximately 70% to 95% of cases of uncomplicated UTIs.1 In the past few years, practitioners and medical facilities began to change the way they managed uncomplicated UTIs because researchers advocated empiric treatment of UTIs for shorter periods of time without cultures. The reason for this was to increase patient compliance and decrease serious adverse drug reactions. By cutting down on the number of days to treat a patient, the patient, the practitioner, or medical facility realize a cost savings. Researchers recommended single dose and 3-day regimens of medications such as trimethoprim/sulfamethoxazole (TMP/ SMX), ciprofloxacin, and others. With this change, a new emerging problem developed: antibiotic resistance.
Antibiotic resistance is now becoming a major factor in uncomplicated community-acquired UTI. Resistance was traditionally a problem only in nosocomial complicated UTI. Because of this emerging resistance problem, relying on the empiric treatment of infections is more challenging for practitioners in the outpatient setting. The prevalence of resistance to TMP/SMX, the current drug of choice in the United States for empiric therapy of uncomplicated UTIs in women, now approaches 18% to 22% in some regions of the United States.2 Not only is there an increase in resistance to TMP/SMX, but within the past 10 years, resistance to ampicillin and cephalothin increased from approximately 20% to between 30% and 40%.2,3
Fortunately, resistance to other agents, such as nitrofurantoin or fluoroquinolone therapies, remains low.4 In the United States, E coli resistance to nitrofurantoin and ciprofloxacin are approximately 2% and 3%, respectively. In Europe, the resistance rate to ciprofloxacin is approximately 2%.5 Although sensitivity rates to various antibiotics have changed, it is important to note that these resistance patterns are not the same across the United States. This is especially true of TMP/SMX. Depending on the area of the country, the sensitivity rate may vary significantly, with the lowest E coli TMP/SMZ susceptibility occuring in the southern and western regions of the United States and a higher susceptibility occurring in the northeastern region.6
In addition to regional predictors, a 1999 study by Wright et al7 suggests that TMP/SMX resistance may be higher in certain identified outpatient populations. Although researchers need to conduct further studies, it appears that current or recent (within the past 3 months) use of TMP/SMX or any antimicrobials increases the risk of having a TMP/SMX-resistant uncomplicated UTI.2
In this study, we report on the results of a retrospective analysis of E coli sensitivities to commonly prescribed antibiotics in the treatment of uncomplicated UTIs at a college health service. We examined the more common antibiotic choices and analyzed their in vitro responses. We compared these results with a previous study we performed in 1993. We sought to determine if there was a change in sensitivity rates of E coli to the more commonly prescribed antibiotics.
METHOD
For this study, we used women who presented to the Stony Brook University Student Health Service with symptoms of uncomplicated UTIs and who had a urine culture and sensitivities showing a colony count greater than 105 colonyforming units per millimeter (cfu/mL) for E coli. We collected specimens by standard clean catch method. We tested susceptibility using the Kirby Bauer disk diffusion method.
From June through December 2003, we performed a retrospective chart review. Using charts and laboratory records, we found 98 female patients to have an uncomplicated E coli infection. We recorded the patients’ ages (range- 18-32 years; M- 22.1 years), E coli sensitivities, and the initially prescribed antibiotic therapy. According to standard laboratory practice, we reported sensitivities to ampicillin, nitrofurantoin, TMP/SMX, cephalothin, ciprofloxacin, tetracycline, doxycycline, and amoxicillin/clavulanate potassium as sensitive, intermediate, or resistant.
FIGURE 1. Percentage of sensitivity of E coli oragnisms to varioius antibiotics used in the treatment of uncomplicated urinary tract infection.
RESULTS
We found great variation in sensitivities of E coli to each of the antibiotics that we studied (see Figure 1). Ciprofloxacin, nitrofurantoin, amoxicillin/clavulanate, and TMP/SMX had the highest sensitivity rates. Ampicillin had the highest resistance rate, followed by tetracycline and doxycycline. Figure 2 shows the initial prescribing trends in the cases of presumptive uncomplicated UTIs at the Stony Brook University Student Health Service. TMP/SMX is the most commonly prescribed antibiotic for the initial treatment of an uncomplicated UTI at the student health service.
COMMENT
Geographic Variation
Presently, there is no systematic surveillance system for monitoring susceptibility profiles of community-acquired UTI isolates in the United States.2 Practitioners have few sources of information about resistance rates in their specific practice areas. Many studies suggest that practitioners should consider local resistance patterns when choosing a first-line agent for treatment of an uncomplicated UTI. The Infectious Diseases Society of America (IDSA) recommends that local communities establish methods to evaluate the susceptibility of urinary tract pathogens in their areas. Our study is a way of becoming vigilant about resistance patterns in a local community.
FIGURE 2. Initial antibiotic prescribed for the treatment of presumptive uncomplicated urinary tract infection.
Treatment Guidelines
Once practitioners establish that empiric treatment is appropriate, they must make a decision regarding the choice of which first-line antibiotic agent to prescribe. As discussed earlier, practitioners should consider the local rate of resistance to antibiotics in making their decision. The 1999 IDSA guidelines for uncomplicated UTI treatment advises that practitioners should consider the empiric use of a 3-day course of TMP/SMX as the current standard therapy. This is particularly true in communities with a TMP/SMX resistance pattern of 10% to 20%. If resistance is less than 10%, practitioners should consider an alternative drug.2 Two agents that the IDSA recommends are fluoroquinolone and nitrofurantoin. Even in areas of relatively higher resistance, practitioners may consider TMP/SMX if the patient has no other risk factors for resistance. If practitioners choose TMP/SMX in this situation, they may need to follow up more closely than they would if they give an alternative therapy.
Summary
Although diagnosis of an uncomplicated UTI remains relatively simple, treatment continues to grow more complex as patterns of local resistance continue to change. For practitioners in community settings to prescribe empiric antimicrobial therapy for patients presenting with UTI symptoms, they must be aware of the local patterns of antimicrobial resistance. This requires that practitioners establish a methodology for examining resistance patterns within the community. Periodic reexamination is desirable, considering the emergence of and changes in resistance patterns over the past several decades. In addition, history taking will reveal additional risk factors for resistance, such as recent or current antimicrobial use.
In this study,our analysis revealed a TMP/SMX sensitivity rate of 86%. We believe that this indicates that, although we may still consider TMP/SMX as a first-line agent in our population, fluoroquinolone or nitrofurantoin may also be reasonable, especially in patients who have an additional risk factor for resistance.
When we compared the results from this study with the results from our 1993 study, in which the sensitivity rate was 87%,8 we found that there was a 1% change over a 10-year period. Given the concern of increasing resistance of E coli to TMP/SMX, we were expecting a more significant increase in resistance in our population. We observed this trend in increasing resistance only slightly in this study. Data related to the prescribing habits of our practitioners in cases of UTIs showed that TMP/SMX was the most prescribed antibiotic.
Because TMP/SMX is the most commonly prescribed antibiotic at Stony Brook University, and because we are concerned with the increasing resistance of E coli to commonly used antibiotics, we will continue to reevaluate the resistance pattern in our population on a regular basis. This will help us determine if there is the need for modifying our initial antibiotic choice of empiric therapy for UTI.
NOTE
For comments and further information, please address correspondence to Robert K. Ansbach, Associate Director/Physician Assistant, Stony Book University Student Health Service, 1 Stadium Road, Stony Brook, NY 11794-3191 (e-mail: ransbach@ notes.cc.sunysb.edu).
REFERENCES
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Robert K. Ansbach, MA, RPA-C; Karen Dybus, MS, RPA-C; Rachel Bergeson, MD
The authors are with the Stony Brook University Student Health Service, NY, where Robert K. Ansbach is the associate director and a physician assistant, Karen Dybus is a physician assistant, and Rachel Bergeson is the medical director.
Copyright HELDREF PUBLICATIONS Sep/Oct 2005
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