APN is a common infectious disease requiring antibiotics. The increasing prevalence of infectious diseases caused by antibiotic-resistant bacteria makes treatment of APN more difficult [7, 10-12]. The characteristics of patients with APN due to urinary tract obstruction have been highly varied, and the clinical standard for diagnosing APN has been unclear in previous studies. In this study, we aimed to establish the resistance patterns of uropathogenic strains isolated from patients with community-acquired OPU.
In this study, fluoroquinolone resistance in uropathogenic Enterobacteriaceae was found to be alarmingly high in OPU cases compared with that in uncomplicated pyelonephritis cases. In prior studies, the rate of fluoroquinolone resistance was higher in complicated UTIs than in uncomplicated UTIs [8, 13, 14]. However, the rate was uncertain in complicated UTIs due to urolithiasis [7, 8]. The reason for this inconsistency might be related to the heterogeneous causative diseases of complicated UTIs. Therefore, we excluded male patients, patients with functional uropathy such as urinary bladder dysfunction, and patients with known obstructive uropathy due to urogenital tumor or other anatomic abnormalities, which are common causes of urinary tract obstruction . Moreover, we performed propensity score matching to reduce the possibility of selection bias.
In this study, fluoroquinolone resistance did not affect the prognosis regardless of the drug resistance of the pathogens. However, patients who received inappropriate empirical treatment in this study were eventually treated with appropriate antibiotics. Thus, appropriate definitive therapy should be emphasized. Further, it could be inappropriate or unsafe to use fluoroquinolones as the initial empirical treatment for patients with OPU showing critical conditions such as sepsis or septic shock. Further studies are needed in this regard.
Complicated UTIs are associated with more severe infectious diseases (such as cases involving septic shock) and high mortality due to obstruction [16-18]. Therefore, broad-spectrum antibiotics including carbapenems are commonly used in complicated UTI cases. In this study, intensive care unit stay, shock, and acute kidney injury were more common in the OPU group. Moreover, carbapenems were also more frequently used in the OPU group. However, no meaningful differences were observed in antibiotic susceptibility (except for fluoroquinolones), clinical outcomes, empirical antibiotics, or prognosis between the two groups. The similarity between the therapies administered in the two groups and the clinical outcomes in this study suggest that APN in patients with ureteral stones can be managed medically in the same way as pyelonephritis in patients without urologic abnormalities.
In complicated UTIs, correcting urologic abnormalities is an important treatment option, and several methods are available for the management of ureteral stones causing obstruction . In this study, no standard protocol was used for relieving urinary tract obstruction, and the decision on whether drainage should be placed depended on the judgment of relevant physicians, including urologists. It is possible that the prompt relief of urinary tract obstruction might have prevented the worsening of the condition and led to better outcomes. However, early drainage was not related to treatment failure in this study (Supplementary Table 2). It is difficult to determine how relief of urinary tract abnormalities can contribute to the treatment of OPU, although prompt relief of urinary tract obstruction is commonly necessary for a cure.
This study had several limitations. First, the study was limited by its retrospective design and the relatively small sample size of patients with OPU. The data were also limited because we were unable to evaluate prior antibiotic use based on the available data from electronic medical records covering our study period. Our goal, however, was to characterize antibiotic resistance patterns and compare them with antibiotic regimen recommendations. Second, relatively high antibiotic resistance was observed in both study groups. This is probably because the study was conducted in a tertiary university hospital. Therefore, the present results may exaggerate the antimicrobial resistance of organisms compared with results obtained in a primary care setting. Third, the relatively small number of included patients did not provide enough study power to demonstrate non-inferiority. Despite the low power of the study, obstructive pyelonephritis was consistently a risk factor for UTI caused by drug-resistant species in prior studies [7, 8, 13, 14]. Our study could be a pilot study evaluating the clinical impact of antimicrobial resistance in OPU.
In summary, the results of this study suggest that antibiotics for patients with APN related to urinary tract obstruction by ureteral stones may be empirically selected in accordance with the treatment protocol for general pyelonephritis. The selection may need to be based on the treatment protocol for severe UTIs accompanied by sepsis or healthcare-associated UTIs as opposed to community-associated UTIs [13, 19-21]. Fluoroquinolones should be used cautiously for OPU because of emerging resistance.