What is urinary catheter and/or ureteral stent encrustation?
Encrustation is the formation of a conditioning film that develops on the surface of the UC or ureteral stent. The exact mechanism is not well understood, but it is believed to involve electrostatic interactions of urinary proteins that stimulate binding onto the stent or UC surface.25 Encrustation increases exponentially with the dwell time. Among patients with ureteral stents placed due to urolithiasis, encrustation occurred in 9.2% of stents removed prior to 6 weeks, 47.5% of stents removed at 6 weeks, and 76.3% of stents removed at 12 weeks.26 Encrustation is most common at the proximal and distal ends (pigtails) of the ureteral stent and usually spares or presents last within the lumen.29 Attempts have been made to prevent ureteral stent encrustation through the development of biodegradable, drug-eluting, and tissue-engineered substrates. These developments are promising, but currently there is limited observational data from large randomized trials to suggest that these new modalities decrease rates of encrustation.25 Encrustation is highly associated with certain microorganisms, especially those that create biofilms.30 Urease-producing bacteria, most commonly P. mirabilis, play a role in encrustation formation.31 Bacteria most commonly associated with encrustation include Proteus species (P. mirabilis is most common), P. aeruginosa, K. pneumoniae, Providencia species (P. stuartii is most common), and M. morganii.
Does ureteral stent bacterial colonization correlate with UTI?
Ureteral stent colonization with bacteria increases with dwell time and is found in 40% to 98.5% of stents placed.32-35 If UTI is suspected in a patient with an active indwelling ureteral stent, a sample of urine should be cultured while the stent is in place.25 Typically, genitourinary and normal skin flora pathogens are found when the ureteral stent is cultured. The top 3 organisms cultured from ureteral stents are S. aureus, P. aeruginosa, and E. faecalis.34 Urine culture usually does not correlate with stent culture results, which has brought up the debate of how bacterial colonization occurs. It has been postulated that colonization is actually a manifestation of contamination during the insertion procedure, but this has yet to be validated.25 In patients with symptoms of UTI in the setting of an indwelling ureteral stent, a positive culture has low sensitivity, with estimates between 21% and 40%.35 Therefore, a negative urine culture does not rule out UTI alone in a symptomatic patient. Multiple studies have suggested that colonization of the ureteral stent does not correlate strongly with developing a UTI.25,32-34
How can UTI be prevented in those receiving PCN or ureteral stent placement?
Antibiotic prophylaxis has been recommended to prevent UTI in patients who will undergo PCN or ureteral stent placement. The American Urological Association recommends empiric treatment even in the absence of signs and symptoms of UTI,36 but substantial evidence is lacking that this approach prevents infection.37 Ciprofloxacin or trimethoprim/sulfamethoxazole has been recommended by some for empiric coverage for enteric gram-negative bacilli and enterococcus in those undergoing genitourinary manipulation or instrumentation.32,38 Most patients who develop CA-UTI and pyelonephritis do so within the first 2 to 6 weeks after placement.37,39 Bacteriuria, candiduria, and/or pyuria are present in all patients approximately within 9 weeks even when sterile urine is confirmed prior to PCN placement.39 Data on the effectiveness of antibiotic prophylaxis to prevent CA-UTI in those with PCN or ureteral stenting is limited. Currently, there are no recommendations from the IDSA on how to prevent infection in these situations.5 Early or frequent stent removal or exchanges has been proven to reduce UTI in those with ureteral stenting.33 Patients with diabetes mellitus and chronic renal failure are at high-risk for UTI when ureteral stents are in place. This population should undergo close monitoring for UTI development and may warrant more frequent stent exchanges.27,40
What is the treatment of CA-UTI associated with PCN and/or ureteral stenting?
The IDSA guidelines do not apply to patients with PCN and/or ureteral stenting.5 There is no treatment protocol for UTI related to these processes. Generally speaking, they are considered “complicated UTI” by most experts. Broad-spectrum, empiric antibiotic administration along with prompt removal of the PCN and/or ureteral stent is the gold standard of therapy.27 The recommended duration of targeted antibiotic therapy is generally between 5 and 14 days.19 Most clinicians will treat this complicated UTI for at least 10 to 14 days. Antibiotic administration should be continued even after removal of the catheter and/or stent to complete the full course. Repeat urinalysis and culture is not indicated at the end of therapy if the patient is clinically improving or has remission of symptoms.
What is the exchange rate for those who require chronic PCN and/or ureteral stent use?
On average a PCN or ureteral stent should be exchanged every 2 to 3 months in patients who require chronic usage.24,27 Some patients with persistent complications may require more frequent exchanges (< 10 weeks).27 Encrustation and bacterial colonization become more prevalent the longer the devices are in place. This process is estimated to begin within the first 2 weeks after placement.27,33,34 A “forgotten stent” is one that has been left in place after the patient is lost to follow-up. This unfortunate event can lead to massive encrustation, UTI, stent fracturing, and complete ureteral obstruction.24 As noted, patients with diabetes mellitus, chronic renal failure, and frequent UTI may warrant more frequent exchanges, but this should be determined on a case-by-case basis.
