Vol. 31 No. 1 Microbiologic outcome in acute pyelonephritis correlates with ESBL or susceptibility:- Uppathamnarakorn P, et al. 15

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1 ORIGINAL ARTICLE Vol. 31 No. 1 Microbiologic outcome in acute pyelonephritis correlates with ESBL or susceptibility:- Uppathamnarakorn P, et al. 15 Microbiologic Outcome in Patients with Acute Pyelonephritis Caused by Enterobacteriaceae Treated with Ceftriaxone Correlates with the Presence of Extended-spectrum Beta-lactamase or In vitro Susceptibility Pannawadee Uppathamnarakorn, M.D. 1, Opass Putcharoen, M.D. 1, Apatcha Puengjitprapai, M.D. 2, Jirayu Visutranukul, M.D. 3, Chusana Suankratay, M.D., Ph.D. 1 1 Division of Infectious Diseases, Department of Medicine, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand. 2 Department of Medicine, Charoenkrung Pracharak Hospital, Bangkok, Thailand. 3 Department of Medicine, Police Hospital, Bangkok, Thailand. ABSTRACT Background: There is still a controversial issue regarding treatment of infection caused by Enterobacteriaceae whether in vitro susceptibility (determined by minimal inhibitory concentration (MIC)) or resistance mechanism (determined by enzyme production) is the most important factor in predicting the treatment outcome. Objective: To determine whether the microbiologic outcome in patients with acute pyelonephritis caused by Enterobacteriaceae correlates with in vitro susceptibility [determined MIC breakpoint] or the presence of extended-spectrum beta-lactamase (ESBL) enzyme. Materials and Methods: A prospective study was carried out in all patients with acute pyelonephritis caused by Enterobacteriaceae hospitalized in 3 hospitals in Thailand from March 2012 to January The microbiologic and clinical outcomes were evaluated at 72 hours after ceftriaxone treatment. All contributing factors as well as in vitro susceptibility and the presence of ESBL of each isolate were determined. Results: During the study period, there were 97 patients with the mean age of ± years. There were 48 (49.5%) patients with MIC breakpoint in the susceptible range. In this susceptibility group, there were 47 (97.9%) patients with microbiologic response. Of 49 patients in the non-susceptibility group, there were 32 (65.3%) patients with microbiological response. Of 97 patients, there were 47 (47.9%) patients infected with ESBL-producing isolate. Of these 47 patients, there were (40.4%) patients with microbiologic response. Of 50 patients infected with non-esbl-producing isolate, there were 49 (98%) patients with microbiologic response. Multiple logistic regression analysis revealed that the factor Keywords: ceftriaxone, acute pyelonephritis, extended-spectrum-beta-lactamase, Enterobacteriaceae, Escherichia coli, Klebsiella pneumoniae, MIC breakpoint, microbiologic outcome Corresponding author: Pannawadee Uppathamnarakorn, M.D., Division of Infectious Diseases, Department of Medicine, Faculty of Medicine, Chulalongkorn University, Bangkok 10330, Thailand. 15

2 16 J INFECT DIS ANTIMICROB AGENTS January-April 2014 determining microbiologic response in acute pyelonephritis patients was ESBL production (odds ratio=8.594, 95% CI , P=0.032). Conclusions: The present study demonstrated that microbiologic outcome in patients with acute pyelonephritis caused by Enterobacteriaceae treated with ceftriaxone may correlate better with the presence of ESBL than in vitro susceptibility. (J Infect Dis Antimicrob Agents 2014;31:15-28.) INTRODUCTION Since the first report of extended-spectrum betalactamase (ESBL)-producing organisms in mid of 80, this is still a problem worldwide regarding infections caused by these strains. 1 In Thailand, between , there was a trend towards the increasing rate of ESBL-producing Escherichia coli isolation in clinical specimens reported by the National Antimicrobial Resistance Surveillance Thailand (NARST) 2 and also an increasing report of community-onset infection caused by ESBLproducing E. coli. 3 In 2007, 42.2% and 35.8% of ESBL-producing Escherichia coli and ESBLproducing Klebsiella species., respectively, were isolated from patients with intraabdominal collection in the Asia-Pacific region. 4 In addition, there are problems with infections caused by ESBL-producing organism in the United States and some parts of Europe. 5 Before 85, the National Committee for Clinical Laboratory Standards (NCCLS) [currently the Clinical Laboratory Standards Institute (CLSI)] established the minimal inhibitory concentration (MIC) breakpoints of cephalosporins against Enterobacteriaceae which correlates very well with the clinical outcome of treatment of infections caused by these organisms. In 86, Brun-Buisson and colleagues reported the first outbreak of infections caused by ESBL-producing Klebsiella pneumoniae. Patients infected with ESBLproducing Enterobacteriaceae may have high mortality and morbidity rates. 6-8 Carbapenems are regarded as the antibiotic of choice for the treatment of serious infections caused by ESBLproducing Enterobacteriaceae In 2005, the CLSIencouraged all microbiological laboratories to perform the screening and confirmation tests of ESBL production among all Enterobacteriaceae. The test interpretations should be reported as resistant to all penicillins, cephalosporins, and monobactams with all confirmed ESBL-producing isolates. 11 In 2010, the CLSI changed the recommendation not to perform routine ESBL production test, and the MIC breakpoints of cephalosporins were lowered among Enterobacteriaceae isolates. 12 There are 3 main reasons behind this statement. 22 The study by Andes and Craig 28 showed that pharmacodynamic target associated with efficacy in cephalosporin treatment depended on the reduced MIC. Another reason is from animal experiments conducted by Maglio and colleagues demonstrating that the treatment outcomes in infections caused by ESBLproducing Enterobacteriaceae were similar with those caused by non-esbl-producing isolates but with comparable MIC. 29 Finally, several clinical studies either retrospective or prospective in design have confirmed the same findings as in animal models. 30,31 However, the evidence that infections caused by ESBL-producing Enterobacteriaceae with low MIC respond to cephalosporin treatment is questionable. 14,23,30 To date, there is still a controversial issue

3 Vol. 31 No. 1 Microbiologic outcome in acute pyelonephritis correlates with ESBL or susceptibility:- Uppathamnarakorn P, et al. regarding treatment of infection caused by Enterobacteriaceae and whether in vitro susceptibility or resistance mechanism is the most important factor in predicting the treatment outcome. The present study was thus aimed to determine whether the microbiologic outcome in patients with acute pyelonephritis caused by Enterobacteriaceae correlates with in vitro susceptibility (determined by MIC) breakpoint or the presence of ESBL enzyme. MATERIALS AND METHODS Study design A prospective study was carried out in all patients with acute pyelonephritis caused by Escherichia coli, Klebsiella pneumoniae, K. oxytoca or Proteus mirabilis in 3 hospitals including King Chulalongkorn Memorial Hospital, Police Hospital, and Charoenkrung Pracharuk Hospital, Bangkok, Thailand. The study period was between March 1, 2012 and January 31, Written informed consent was obtained from all patients, and the institutional review board at King Chulalongkorn Memorial Hospital approved the protocol. Patients The inclusion criteria included the patients older than 18 years old with a documented episode of either community-acquired or nosocomial acute pyelonephritis caused by E. coli, K. pneumoniae, K. oxytoca or P. mirabilis. The exclusion criteria included 1) pregnancy or lactation, 2) contraindication for cephalosporins and 3) expected death within 48 hours. Microbiological methods All isolates were identified at the site laboratory, and the pathogens were tested for in vitro susceptibility by the disk diffusion method. All isolates were sent to King Chulalongkorn Memorial Hospital laboratory to determine the MIC of ceftriaxone by Epsilon (E) test. In the present study, we used the MIC breakpoint recommended by the CLSI to determine the susceptibility of the isolates. The criteria included 1) susceptibility: MIC of 1 μg/ml, 2) intermediate susceptibility: MIC of >1-< 4 μg/ ml and 3) resistance: MIC of 4 μg/ml. All isolates were tested for the ESBL production by the combined-disk method, according to the CLSI recommendation. Clinical analysis The data collected from patients included the demographic, clinical, and laboratory data. The preexisting conditions considered as possible risk factors included diabetes mellitus (DM), renal failure (RF), cerebrovascular disease (CVD), previous hospitalization, previous antibiotic use, and previous urinary tract infection (UTI). All patients were treated with intravenous ceftriaxone 2 g once daily. The primary end point of the study was to determine which contributing factors especially in vitro susceptibility and the presence of ESBL will be associated with the microbiologic outcome at 72 hours of ceftriaxone treatment. The secondary end point was to determine which contributing factors will be associated with the clinical outcome at 72 hours of ceftriaxone treatment. Definitions 18 Definitions were defined a priori. Fever was defined as an oral temperature of > 37.8 C. Acute pyelonephritis was defined as one of all of the

4 18 J INFECT DIS ANTIMICROB AGENTS January-April 2014 following presentations within 48 hours including fever, chills, urinary urgency, urinary frequency, flank pain, or costovertebral angle (CVA) tenderness, with pyuria of > 10 white blood cells per highpower field (HPF) and positive urine culture of > 10 5 colony-forming units (CFU)/mL. The microbiologic outcomes assessed at 72 hours of treatment were defined as sterilization of urine (the urine culture grew < 10 4 CFU/mL), persistence (the urine culture grew > 10 4 CFU/mL), or superinfection (the urine culture grew > 10 5 CFU/ ml of a pathogen other than the baseline pathogen during treatment). The microbiologic outcome was classified into a good or poor outcome. A good outcome was defined as no persistence of infection, and a poor outcome was defined as persistence of infection or superinfection. The clinical severity was classified into marked, moderate, and mild severities. Marked severity was defined as unstable vital signs or sepsis. Moderate severity was defined as fever > 39 C, severe flank pain, nausea, vomiting, or blood leukocytosis > 15,000 cells/mm 3. Mild severity was defined as absence of definition for severe and moderate severities. The clinical outcome was assessed at 72 hours of treatment. A good outcome was defined as resolution of the signs and symptoms of UTI, and a poor outcome was defined as persistence of fever, flank pain, or other signs and symptoms of UTI as well as death. Statistical Analysis We calculated sample size by using the formula in logistic regression to compare association of different risk factor. n total = p (1 p) (k + 1) (1 + k) z +z1 1 p 2 k - 2 (1 p 2 ) β + (p 2 p 1 ) 2 p 1 (1 p 1 ) k 2 N total,adjusted = N total [1/1-p 2 1,2,...,m] P1 indicates the mean proportion of patients infected with ceftriaxone-susceptible strain who have good microbiologic outcome; P1 equaled P2 indicates the mean proportion of patients infected with ceftriaxone-resistant strain who have good microbiologic outcome; P2 equaled 0.3. P is the prevalence of acute pyelonephritis in patients that were hospitalized due to acute fever with chills; P equaled 0.8. The p1, 2, 3,...m indicate all variable factors associated with treatment outcome in patients with acute pyelonephritis. The alpha was 0.05, and beta was 0.8. Finally, the calculated sample size was 110. Discrete variables were tested by using X 2, and continuous variables were tested by using Student s T test. A multivariate logistic regression model was used to assess factors attributed to microbiological outcome. The logistic model was developed by entering all variables with P-value of < 0.2 in the univariate analysis into the initial model. Estimated odds ratios and 95% confidence intervals were estimated from these models. All analysis was performed using SPSS version and P-value of 0.05 was considered statistically significant.

5 Vol. 31 No. 1 Microbiologic outcome in acute pyelonephritis correlates with ESBL or susceptibility:- Uppathamnarakorn P, et al. RESULTS During the period of study, 107 patients with acute pyelonephritis were enrolled but 10 were excluded due to incomplete data. The causative agents included 84 (86.6%) E. coli and 13 (13.4%) K. pneumoniae. Demographic and clinical characteristics (Table 1) Of 97 patients, there were 73 (75.3%) females with the mean age of 73.2 years (range: years). Fifty-six (57.7%) patients had predisposing conditions to acute pyelonephritis. The most common condition was neurogenic bladder (27 patients, 27.8%), followed by benign prostatic hyperplasia (16, 16.5%) and malignancy (5, 5.2%). The most common comorbidity was diabetes, found in 44 patients (45.4%). There were 52 (53.6%), 48 (49.5%), and 31 (32%) patients with previous antibiotic use within 3 months, hospitalization within 3 months, and previous UTI, respectively. Community-acquired infection was noted in 58 (59.8 %) patients. Microbiology testing (Table 2) Regarding cephalosporin susceptibility, 48 (49.5%) isolates were susceptible to ceftriaxone, ceftazidime, and cefepime. Eighty-seven (89.7%) and 60 (61.8%) isolates were susceptible to piperacillin/tazobactam and amoxicillin/clavulanate, respectively. Only 1 isolate was resistant to carbapenems. Regarding aminoglycoside susceptibility, only 3 (3.1%) isolates were resistant to amikacin. MIC range (Table 3) Of 97 isolates, there were 48 (49.5%), 0, and 49 (50.5%) isolates with susceptibility ( 1 μg/ml), intermediate resistance (> 1- < 4 μg/ml), and resistance ( 4 μg/ml) to ceftriaxone, respectively. There were no isolates with the MIC of μg/ ml. Of 47 ESBL-producing isolates, there were 47 (100%) isolates with resistance to ceftriaxone. Of 50 non-esbl-producing isolates, there were 48 (96%) and 2(4%) isolates with susceptibility and resistance to ceftriaxone, respectively. ESBLs production Forty-seven (48.5%) isolates produced ESBL. There were five patients (10.1%) who had steroid use in ESBL producing group and none in non-esbl producing group. Thirty-five patients ( 36.1%) had antibiotics within 3 months in the ESBL producing group while seventeen patients (.5 %) in the non- ESBL producing group had used antibiotics within 3 months. A history of previous urinary tract infection was found in ESBL producing and non- ESBL producing groups, 26 ( 26.8%) and 5 (5.1%), respectively. Microbiologic outcome (Table 4, 5) Sixty-eight patients (70.1%) had a good microbiologic outcome. There were 48 (49.5%) patients with MIC breakpoint in the susceptible range. In this susceptibility group, there were 47 (97.9%) patients with microbiologic response. Of 49 patients in the non-susceptibility group, there were 32 (65.3%) patients with microbiological response. Of 97 patients, there were 47 (47.9%) patients infected with ESBL-producing isolate. Of these 47 patients, there were (40.4%) patients with microbiologic response. Of 50 patients infected with non-esbl-producing isolate, there were 49 (98%) patients with microbiologic response. There were no patients in the present study that had a superinfection. In the univariate analysis, previous antibiotic use within 3 months (relative risk 1.46 (1.124, 1.907

6 20 J INFECT DIS ANTIMICROB AGENTS January-April 2014 Table 1. A comparison of variables between patients with good microbiologic and poor microbiological outcome. Variables Microbiologic outcome G ood (%) Poor (% ) Total P value Gender Female 52 (71.23) 21 (28.77) 73 <0.001 Male 16 (66.67) 8 (33.33) Age Hospital CKP 40 (51.54) 15 (48.46) KCMH 4 (100.00) POLICE 24 (63.16) 14 (36.84) M echanical obstruction 13 (76.47) 4 (23.53) BPH Neurological bladder Foley 13 (81.25) 3 (.75) (65.52) 10 (34.48) (70.37) 8 (29.63) S teroid 2 (40.00) 3 (60.00) Immunosuppressive agent Diabetes CVD Previous ATB in 3 months Previous hospitalization in 3 months History of UTI in 6 months 1 (33.33) 2 (66.67) (67.39) 15 (32.61) (73.08) 7 (26.92) (57.69) 22 (42.31) (70.83) 14 (29.) (45.16) (54.84) Type of infection Communit y 58 (72.50) 22 (27.50) 80 <0.001 Hospital 10 (58.82) 7 (41.18) Fever Chills 68 (70.10) 29 (29.90) 97 < (69.10) (30.90) V omiting 26 (83.87) 5 (16.13) Frequency of urination Flank Pain (61.29) 12 (28.71) (82.35) 3 (.65) Causative agents E. coli 60 (71.43) 24 (28.57) 84 <0.001 K. pneumoniae 8 (61.54) 5 (39.46) Bacteremia 13 (81.25) 3 (18.75) ESBL production Ye s (40.43) 28 (59.57) No 49 (98.00) 1 (2.0) 50 <0.001 MIC to Ceftriaxone Susceptible 47 (97.92) 1 (2.08) 48 <0.001 Resistant 21 (42.86) 28 (57.14) CKP: Charoenkrung Pracharak Hospital, KCMH: King Chulalongkorn Memorial Hospital, Police: Police Hospital, BPH: benign prostatic hyperplasia, ESBL: extended-spectrum Beta-lactamase, MIC: minimal inhibitory concentration, UTI: urinary tract infection, ATB: antibiotic, CVD: cerebrovascular disease, E. coli: Escherichia coli, K. pneumonia: Klebsiella pneumoniae

7 Vol. 31 No Microbiologic outcome in acute pyelonephritis correlates with ESBL or susceptibility:- Uppathamnarakorn P, et al. Table 2. Data of susceptibility of isolates. Drug Susceptible Number of isolates Intermediate Resistant Ceftriaxone Ceftazidime Cefepime Gentamicin Amikacin 94-3 Trimethoprim/sulfamethoxazole Ciprofloxacin Ampicillin Amoxicillin/clavulanate 60 Piperacillin/tazobactam Meropenem 96-1 Imipenem 96-1 Ertapenem Table 3. Number of patient and MIC value. Organism < (0.0625, (0.125, Number or patient in (0.25, MIC ( μg/ml) value range ( 0.5, 1) ( 1, 2) ( 2, 4) ( 4, 8) ( 8, 16) ( 16, 32) > 32 Total 0.125) 0.25) 0.5) E. coli ESBLs Positive production Negative K. pneumoniae ESBLs Positive production Negative E. coli : Escherichia coli, K. pneumonia: Klebsiella pneumonia, ESBL: extended-spectrum beta-lactamase, MIC: minimal inhibitory concentration 21

8 22 J INFECT DIS ANTIMICROB AGENTS January-April % confidence interval), p value=0.004), previous urinary tract infection in 6 months (RR 1.81(1.209, % CI), p value < 0.991), MIC susceptible to ceftriaxone (RR 2.85 (1.649, % CI), p value < 0.001), ESBLs production (RR 2.42 (1.709, % CI), p value < 0.001) were significantly associated with microbiological outcome. In the multivariate analysis, independent risk factor significantly associated with microbiological outcome was ESBLs non-production, with odd ratio 8.59 (1.208, % confidence interval, p value = 0.032) (Table 4). Clinical outcome (Table 6, 7) Good clinical outcome was observed in 78 (80.4%) patients. In the univariate analysis, all of these factors including previous antibiotic use in 3 months (relative risk 1.42 (1.163, 1.733, 95% confidence interval) p value <0.001), previous urinary tract infection in 6 months (RR (1.089, % CI) p value = 0.001), in vitro susceptibility to ceftriaxone (RR (1.18, % CI) p < 0.001), and ESBL production (RR (1.204, % CI) p value < were significantly associated with good clinical outcome. Table 4. Univariate analysis of independent variables associated for microbiologic outcome. Variables N Good microbiologic outcome P ercentage Relative risks (CI) P value Age <65 years.5% (0.664, 1.248) Female Gender % (0.777, 1.469) Mechanical obstruction % (0.665, 1.216) Benign prostatic hyperplasia % (0.632, 1.105) Neurogenic bladder.6% (8.813, 1.489) 0.5 Foley catheter.6% (0.745, 1.328) Steroid 2 2.1% (0.608, 5.287) Immunosuppressive agent 1 1.0% (0.429, ) Diabetes % (0.828, 1.400) 0.58 Cerebrovascular accident.6% (0.713, 1.250) Previous antibiotic in 3 months % (1.124, 1.907) Previous hospitalization in 3 months % (0.755, 1.270) History of UTI in 6 months % (1.209, 2.714) < Community-acquired infection % (0.810, 1.876) MIC susceptible to ceftriaxone % 2.85 (1.649, 3.165) < ESBL production % (1.709, 3.438) < ESBL: extended-spectrum Beta-lactamase, MIC: minimal inhibitory concentration, UTI: urinary tract infection

9 Vol. 31 No Microbiologic outcome in acute pyelonephritis correlates with ESBL or susceptibility:- Uppathamnarakorn P, et al. Table 5. Multivariate analysis of variable factors associated with microbiologic outcome. Variables Odds ratio 95% confidence interval P value ESBL Production ( 1.208, 61.1) MIC susceptible to ceftriaxone ( 0.4, ) Previous antibiotic in 3 months ( 0.305, 3.507) History of UTI in 6 months ( 0.589, 5.906) ESBL: extended-spectrum beta-lactamase, MIC: minimal inhibitory concentration, UTI: urinary tract infection Table 6. Univariate analysis of independent variables associated for clinical outcome. Variables N Good clinical outcome P ercentage Relative risks (CI) P value Age <65 years % (0.807, 1.254) Female Gender % (0.850, 1.413) Mechanical obstruction % (0.760, 1.242) Benign prostatic hyperplasia % (0.727, 1.121) Neurogenic bladder % (0.746, 1.096) Foley catheter % (0.756, 1.126) Steroid 3 3.1% (0.660, 2.798) Immunosuppressive agent 2 2.1% (0.542, 2.716) Diabetes % (0.907, 1.354) Cerebrovascular accident % (0.837, 1.347) 0. 6 Previous antibiotic in 3 months % (1.163, 1.733) < Previous hospitalization in 3 months % (0.937, 1.395) History of UTI in 6 months.6% (1.089, 1.953) Community acquired infection % (0.800, 1.411) MIC susceptible to ceftriaxone % (1.187, 1.815) < ESBL production % (1.204, 1.879) < ESBL: extended-spectrum beta-lactamase, MIC: minimal inhibitory concentration, UTI: urinary tract infection 23

10 24 J INFECT DIS ANTIMICROB AGENTS January-April 2014 Table 7. Multivariate analysis of variable factors associated with clinical outcome. Variables Odds ratio 95% confidence interval P value ESBL Production ( 0.655, ) MIC susceptible to ceftriaxone ( 0.123, 5.728) Previous antibiotic in 3 months ( 0.814, ) History of UTI in 6 months ( 0.567, 5.516) ESBL: extended-spectrum beta-lactamase, MIC: minimal inhibitory concentration, UTI: urinary tract infection In the multivariate analysis, no independent risk factor significantly associated with good clinical outcome was observed. DISCUSSION To date there have been increasing reports of infections caused by multidrug-resistant organisms worldwide. In the present study, there were 47 (48.5%) ESBL-producing isolates which were higher than the prevalence of 30% reported by Suankratay and colleagues in This was probably due to the differences in the study period and number of enrolled hospitals. In the present study, there were 68 (70.1%) patients with good microbiologic outcome. Even though in the univariate analysis, 4 variable factors including in vitro susceptibility, the presence of ESBL, previous antibiotic use within 3 months, and previous UTI within 6 months were significantly associated with good microbiological outcome. However, in the multivariate analysis, only the absence of ESBL was significantly associated with good microbiologic outcome. These findings emphasize that the microbiologic outcome in patients with acute pyelonephritis caused by Enterobacteriaceae treated with ceftriaxone may correlate better with the presence of ESBL than in vitro susceptibility. A retrospective study in patients with bacteremia caused by cefepime-susceptible ESBL-producing Enterobacteriaceae showed that patients receiving cefepime treatment were more likely to have a clinical failure and 30-day mortality than those receiving carbapenem treatment. 21 A recent case-control study in patients with bacteremia caused by either ESBL- and non-esbl-producing E coli demonstrated that an inappropriate empirical therapy was observed in 39 of 49 (80%) and 6 of 94 (6.4%) patients with ESBL and non-esbl bacteremia. 15 The mortality rate was 18% and 7% in the ESBL and non-esbl groups, respectively. The treatment failure was observed in 4 of 7 (57.1%) patients treated with ceftazidime despite the causative agent susceptibilty to ceftazidime but with ESBL production. 15 There have been accumulating reports which showed that clinical outcome might correlate better with in vitro susceptibility than with the resistance mechanism. 24,32,33 There was a recent study by Paterson and colleagues in 32 patients with cephalosporin-susceptible ESBL-producing K. pneumoniae bacteremia treated with cephalosporins. 6 All 6 patients infected with the strain of MIC of 8 μg/ ml had no response to cephalosporin treatment, whereas clinical failure was observed in only 3 of 11 (27%) patients infected with the strain of MIC of < 2 μg/ml. Another study in 2004 in Korea showed

11 Vol. 31 No Microbiologic outcome in acute pyelonephritis correlates with ESBL or susceptibility:- Uppathamnarakorn P, et al. that favorable outcome was noted in all patients infected with ESBL-producing K. pneumoniae with MIC of < 2 μg/ml who were treated with cephalosporin. 13 In contrast, only 1 (33.3%) patient infected with the strain of MIC of 8 μg/ml responded to cephalosporin treatment. In the present study, the presence of ESBL is the only important factor associated with good microbiologic outcome in ceftriaxone treatment of acute pyelonephritis caused by Enterobacteriaceae, in comparison with in vitro susceptibility. This finding maybe explained by the fact that there was the bimodal distribution of MIC values among our 32 (32.9%) and 43 (43.3%) isolates with MIC of < and MIC > 32 μg/ml, respectively. (Table 3); there were no isolates with the MIC of μg/ml. In addition, there were no ceftrixone-susceptible isolates among ESBL-producing Enterobacteriaceae. Hence, the implementations of our results to clinical practice should be confirmed by future studies in patients infected with isolates of all MIC values. A recent meta-analysis by Falagas and colleagues was aimed to evaluate the impact of MIC values within the susceptible range on clinical outcome. 20 They found that there was an association between the high MIC values within the susceptible range and adverse outcomes. Surprisingly, of 47 patients infected with ESBLproducing starin, there were (40%) and 39 (63.7%) patients with good microbiologic outcome and clinical outcome, respectively. These numbers are interestingly high and comparable to previous studies. A study in 36 pediatric patients with 42 episodes of UTI caused by ESBL-producing Enterobacteriaceae showed that there was no significant difference in outcome between carbapenem and non-carbapenem treatment. 26 Another post hoc study in Spain in patients with 25 bacteremia caused by ESBL-producing E. coli demonstrated that there was no statistically significant difference in the mortality when treatment of UTI with secondary bacteremia with piperacillin/tazobactam regardless of the MIC of the pathogen. 27 There are some limitations in the present study. We did not determine the type of ESBL enzymes among Enterobacteriaceae isolates which may affect the microbiologic and clinical outcomes when treatment of these infections with ceftriaxone. It has been shown that infections caused by the strains with different types of ESBL were variably responsive to treatment with different kinds of cephalosporins. Another limitation is that there were no results of microbiologic and clinical outcomes at longer follow-up periods after ceftrixone treatment. In conclusion, to our knowledge, the present study is the first prospective multicenter study to determine the factors associated with microbiologic and clinical outcomes in patients with acute pyelonephritis caused by Enterobacteriaceae. The present study showed that the microbiologic outcome in patients with acute pyelonephritis caused by Enterobacteriaceae treated with ceftriaxone may correlate better with the presence of ESBL than in vitro susceptibility. ACKNOWLEDGEMENTS The present study was supported by Ratchadapiseksompotch Fund, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand. We thank Dr. Thanin Asawavichienjinda, Division of Clinical Epidemiology, Department of Medicine, Faculty of Medicine, Chulalongkorn University who help us in statistical analysis. We also wish to thank the Departments of Microbiology of Chulalongkorn

12 26 J INFECT DIS ANTIMICROB AGENTS January-April 2014 University, Charoenkrung Pracharuk Hospital and Police Hospital for their assistance in this study. Potential conflicts of interests All authors have no conflicts of interests. References 1. Brun-Buisson C, Legrand P, Philippon A, Montravers F, Ansquer M, Duval J. Transferable enzymatic resistance to third-generation cephalosporins during nosocomial outbreak of multiresistant Klebsiella pneumoniae. Lancet 87;2: Apisarnthanarak A, Buppunharun W, Tiengrim S, Sawanpanyalert P, Aswapokee N. An overview of antimicrobial susceptibility patterns for gramnegative bacteria from the National Antimicrobial Resistance Surveillance Thailand (NARST) program from 2000 to J Med Assoc Thai 2009;92 Suppl 4:S Polwichai P, Trakulsomboon S, Dejsirilert S, et al. Long-term study of Escherichia coli and Klebsiella pneumoniae isolates producing extended-spectrum beta-lactamases. J Med Assoc Thai 2009;92 Suppl 4:S Hawser SP, Bouchillon SK, Hoban DJ, Badal RE, Canton R, Baquero F. Incidence and antimicrobial susceptibility of Escherichia coli and Klebsiella pneumoniae with extended-spectrum beta-lactamases in community- and hospital-associated intraabdominal infections in Europe: results of the 2008 Study for Monitoring Antimicrobial Resistance Trends (SMART). Antimicrob Agents Chemother 2010;54: Hoban DJ, Biedenbach DJ, Mutnick AH, Jones RN. Pathogen of occurrence and susceptibility patterns associated with pneumonia in hospitalized patients in North America: results of the SENTRY Antimicrobial Surveillance Study (2000). Diagn Microbiol Infect Dis 2003;45: Paterson DL, Ko WC, Von Gottberg A, et al. Outcome of cephalosporin treatment for serious infections due to apparently susceptible organisms producing extended-spectrum beta-lactamases: implications for the clinical microbiology laboratory. J Clin Microbiol 2001;39: Lautenbach E, Patel JB, Bilker WB, Edelstein PH, Fishman NO. Extended-spectrum beta-lactamaseproducing Escherichia coli and Klebsiella pneumoniae: risk factors for infection and impact of resistance on outcomes. Clin Infect Dis 2001;32: Tumbarello M, Spanu T, Sanguinetti M, et al. Bloodstream infections caused by extended-spectrumbeta-lactamase-producing Klebsiella pneumoniae: risk factors, molecular epidemiology, and clinical outcome. Antimicrob Agents Chemother 2006;50: Paterson DL, Bonomo RA. Extended-spectrum betalactamases: a clinical update. Clin Microbiol Rev 2005;18: Ramphal R, Ambrose PG. Extended-spectrum betalactamases and clinical outcomes: current data. Clin Infect Dis 2006;42 Suppl 4:S Clinical and Laboratory Standards Institute. Performance standards for antimicrobial disk susceptibility tests; approved standard-tenth edition. Report No.: M02-A9. Wayne, PA: CLSI, Clinical and Laboratory Standards Institute. Performance standards for antimicrobial susceptibility testing; Twentieth informational supplement: M100-S20. Wayne, PA: CLSI, Kang CI, Kim SH, Kim DM, et al. Risk factors for and clinical outcomes of bloodstream infections caused by extended-spectrum beta-lactamase-producing Klebsiella pneumoniae. Infect Control Hosp Epidemiol 2004;25: Suankratay C, Jutivorakool K, Jirajariyavej S.

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