The Risk of Persistent Bacteriuria after Extracorporeal Shock Wave Lithotripsy of Infection Stones: A Prospective Study
Extracorporeal shock wave lithotripsy (ESWL) effectively pulverizes infected (struvite) renal calculi. However, after ESWL minute residual fragments which may harbor bacteria and cause persistent bacteriuria can remain in the renal collecting system for months. We investigated prospectively the incidence of persistent Proteus mirabilis bacteriuria after ESWL among 20 consecutive women with P. mirabilis urinary tract infections and struvite calculi. All patients received parenteral gentamicin for three to 13 (mean 4.9) days immediately before and after ESWL. Oral antimicrobials were then administered for 14 to 70 (mean 31) days. Fifteen patients maintained a sterile urine or experienced urinary reinfection by other organisms during five to 22 (mean 14) months of subsequent bacteriologic surveillance. Nine of these 15 patients had residual fragments at last follow-up. Five patients developed P. mirabilis bacteriuria after one to seven months of surveillance. Three of these five patients had residual fragments. The mean stone size, methods of and duration of renal drainage procedures, and duration of antimicrobial therapy were similar for the two patient groups. P. mirabilis was isolated from the cultures of only three of 16 retrievable stone fragments. In contrast to intact infected renal calculi, residual stone fragments after ESWL are often susceptible to sterilization with antimicrobials.
Infected renal calculi (struvite calculi) are caused by infection of the urine with bacteria that synthesize the enzyme urease.1,2,3,4 Ammonium is released by the breakdown of urea by urease; the urine becomes highly alkaline, and magnesium ammonium phosphate (struvite) and carbonate apatite crystallize.5 Incorporation of the infecting bacteria within the developing stone results in a focus of infection that is resistant to conventional antimicrobial therapy and is manifested clinically by repetitive urinary tract infections caused by the infecting organism (persistent bacteriuria).1,6,7,8 Removal of infection stones is recommended, usually to prevent renal damage due to obstruction and infection and to eradicate the source of persistent bacteriuria. Complete removal of the calculus is generally required for bacteriologic cure.2,3,4,7,9
ESWL is now accepted as the preferred treatment for most renal and upper ureteral calculi.10 Calculi composed of struvite and apatite are susceptible to pulverization. However, minute stone fragments usually remain in the renal collecting system for weeks to months. The possibility that this material may harbor the infecting bacterium and may perpetuate persistent bacteriuria has not been systematically investigated. We studied prospectively the incidence of persistent bacteriuria among 20 consecutive women with infection stones after treatment with ESWL and after a standardized regimen of antimicrobial therapy. Our experience with the first 15 patients in this series has been published previously in the Journal of Urology.
KeywordsShock Wave Lithotripsy Extracorporeal Shock Wave Lithotripsy Stone Fragment Residual Fragment Bacteriologic Cure
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