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New England Section of the American Urological Association

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Risk Factors for Polymicrobial Stones in Patients Undergoing PCNL
William C. Daly, BS1, Erin Santos, PA-C2, Christopher Stockdale, MD2, Johann Ingimarsson, MD2.
1Maine Medical Center Research Institute, Center for Outcomes Research and Evaluation, Portland, ME, 2Maine Medical Center Department of Urology, Portland, ME.

Background: Numerous studies have shown discordance between voided urine culture (UC) and stone culture (SC). This study sought to determine the correlation between polymicrobial stones and sepsis following percutaneous nephrolithotomy, and given poor concordance between UC and SC, other predicting factors for polymicrobial stones in patients undergoing PCNL.
METHODS: Retrospective chart review was performed on 153 consecutive patients who underwent PCNL at Maine Medical Center between October 2016 and December2018. Patient demographic factors, comorbidities, infection history, culture data, stone factors and surgical factors were recorded. Sepsis was defined by SIRS criteria for severe sepsis. Multivariate logistic regression was used to evaluate categorical variables.
RESULTS: 17 of 153 (11%) patients were found to have polymicrobial stones. Of those, 7 (41%) developed post-operative sepsis as compared to 3/33 (9%) in single organism stones and 4/103 (4%) in sterile stones. Presence of polymicrobial stone was significantly associated with post-op sepsis (OR 18, p=0.001). Diabetes (OR 7.7; p=0.003), neurogenic bladder (OR 11.7; p=0.001) a history of urosepsis (OR 6.5; p=0.005), stone diameter >= 26mm (OR 3.8; p= 0.026), and infected stone as indication (OR 9.08; p=0.001) were all independently associated with polymicrobial stone. Limited upper or lower extremity mobility (OR 31; p<0.001), neurologic disease (OR 8.95; p=0.001) (specifically multiple sclerosis (MS) (OR 6.3; p=0.040)) and contractures (OR 55; p=0.002) were associated with polymicrobial stones. While indication for PCNL because of infected stone, or having any positive pre-op urine culture had high specificity and negative predictive value for predicting polymicrobial stone, positive predictive value was low (0.27 and 0.19, respectively) (Table 1). However, combining these with information on DM, MS, spina bifida, ileal conduit or limited lower extremity mobility resulted in high positive predictive values, negative predictive value and specificity (Table 1).
CONCLUSIONS: Patients with polymicrobial stones have a substantially higher risk of post PCNL sepsis compared to stones with a single or no microbe species. There are a number of easily identifiable patient attributes significantly associated with polymicrobial stones. These allow for simple risk stratification to help identify PCNL patients at higher risk for polymicrobial stone and therefore sepsis and have implications for instituting modified treatment strategies such as broader peri-operative antibiotics. Further research is needed to study the effect of these strategies.


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