A Multi-Institutional Study of Struvite Stones: Patterns of Infection and Colonization

Objective: To examine urine and stone bacteriology of struvite stone formers in a large cohort of patients undergoing percutaneous nephrolithotomy (PCNL). Materials and Methods: A total of 1191 patients, with stone and urine cultures, treated with PCNL for renal calculi were included in the study. Statistical differences were assessed using Mann-Whitney U and T-tests. Results: Stone cultures were positive in 72% of patients with struvite stones. Urea-splitting organisms accounted for only half of the positive stone cultures. Enterococcus (9/50, 18%), Proteus (9/50, 18%), and Escherichia coli (6/50, 12%) were the most commonly identified organisms. Notably, two-thirds of struvite formers with negative stone culture had at least one positive culture for a urea-splitting organism on urine culture going back 1 year from the time of surgery. A majority (67%) of struvite stone cultures were found to be resistant to first-and second-generation cephalosporins. Conclusions: The bacteriology of struvite stones has shifted away from traditional urea-splitting organisms and antibiotic coverage must be expanded to include organisms such as Enterococcus that do not respond to cephalosporins. Causative organisms may be found by going back in time to identify the initial organism that could have induced struvite stone formation to inform preventative therapy.