The genitourinary tract is a complex filtering and plumbing system. It can be attacked by microbial invasion at many intersections, creating diagnostic challenges and making localization of infections difficult. Much of the medical literature has concentrated on catheter-associated urinary tract infection (CA-UTI). While the threat of an indwelling catheter sets one backdrop of complexity, there are other conditions that predispose to complex UTI such as renal stones, ureteral diverticula, transplantation of the kidney and bladder, renal stents, chronic prostate disease, genital prosthesis, and ileal urinary drainage. The care team should discuss a method of collecting urine, transport to the clinical microbiology laboratory, and the meaning of bacterial (or fungal) quantitation that will be reported. Colony counts of bacteria and fungi in the setting of an abnormal or instrumented urinary tract are probably the greatest challenge to interpretation of infection. In this chapter, we discuss the current status of practical approaches to diagnosis and management of complex UTIs.
APPROACH TO THE PATIENT
Health care-associated urinary tract infection (HA-UTI) is a major cause of morbidity in hospitalized patients responsible for more than 40% of nosocomial infections. The most common bacterial specter of CA-UTI reflects the patients’ own colonicflora. Other organisms are usually not found until the duration of catheterization exceeds 30 days.1 Patients with long-term indwelling catheters tend to have polymicrobial bacteriuria, making laboratory interpretation difficult. Although Escherichia coli is the most common organism isolated, increasing use of broad-spectrum anti-microbials in health care has contributed to the emergence of multidrug-resistant pathogens. CA-UTI has served as an expanding reservoir for spread of such resistant pathogens as Staphylococci and Enterococci in health care settings. Other pathogens commonly found in HA-UTI include Pseudomonas, Klebsiella, Enterobacter, Proteus, Citrobacter, Acinetobacter, Serratia, Group B streptococci, yeast, and new fungal pathogens.2 When HA-UTI is associated with bacteremia, Enterococcus and Candida are the most common pathogens.3 The major predisposing factors to the development of nosocomial UTI are instrumentation of the genitourinary tract, most commonly presence of a urinary catheter, cystoscopy, underlying illness, diabetes, older age, and more advanced urologic procedures.
METHODS FOR LOCALIZATION
Criteria and definitions of UTI have changed in recent years.4 Asymptomatic bacteriuria (ASB) (no clinical, histologic, or immunologic signs of infection) or candiduria are no longer considered “infection” and may better be described as “colonization.” Under certain circumstances such as pregnancy, transurethral resection of the prostate, or traumatic genitourinary interventions associated with mucosal bleeding, ASB may be regarded as a precursor to development of symptomatic UTI and requires therapy to reduce the risk of associated complications such as bacteremia and sepsis.5 Moreover, the recently modified CDC/NHSN surveillance guidelines introduce two new broad categories of symptomatic urinary tract infection and asymptomatic bacteremic urinary tract infection.6
A bacterial urinary tract infection is defined as the presence of bacteria in the urine in appropriate quantitative counts, pyuria, and symptoms or signs compatible with inflammation. A urine dipstick test is utilized as a screening tool for diagnosis of UTI. The dipstick nitrite test depends on the conversion of nitrate to nitrite by most bacteria in the urine (most often Enterobacteriaceae); normally, no detectable nitrite is present. Leukocyte esterase corresponds to pyuria. Clinical evaluation is always necessary because of the possibility of false-positive and false-negative test results.7
Urine samples for culture and sensitivity should be obtained prior to initiation of antibiotics. If ongoing catheterization is needed, ideally the catheter should be replaced prior to collecting a urine sample for culture in order to avoid culturing bacteria present in the microbial biofilm of the catheter and not within the bladder. In the absence of an indwelling urinary catheter, UTI is likely present when the level of bacteria in the urine is equal to or >105 CFU/mL in a “clean catch” specimen, or equal to or >102 CFU/mL in a catheterized specimen when there are symptoms attributable to the genitourinary tract. Diagnostic criteria of CA-UTI, catheter-associated asymptomatic bacteriuria (CA-ASB), and ASB in the absence of an indwelling catheter in adults are briefly summarized in Table 32-1.8
Clinical presentation may vary from severe obstructive acute pyelonephritis with imminent urosepsis to a catheter-associated postoperative UTI, with spontaneous resolution as soon as the catheter is removed. Diagnostic challenge arises when clinical symptoms of UTI are obscured by presence of the catheter9 or when the patient is elderly, debilitated, or immunosuppressed. A patient’s presentation with otherwise unexplained systemic manifestations compatible with infection (like fever, malaise, altered mental status, fall in blood pressure, leukocytosis, metabolic acidosis, respiratory alkalosis) should prompt evaluation for UTI.
HA-UTI is often associated with a urologic procedure such as placement of a ureteral stent. Bacterial stent colonization plays an essential role in the pathogenesis of stent-associated infections. Risk for stent colonization and UTI is significantly enhanced by the duration of stent retention (colonization is common if the indwelling time is more than 2 weeks), female sex, diabetes mellitus, chronic renal failure, and malignancies.10 Proper culturing of stents can be challenging and is not needed when the same microorganisms grow repeatedly in routine urine cultures; however, difficulty may arise if significant biofilm formation has occurred as routine culture techniques do not accurately detect microorganisms embedded in these biofilms.
During manipulation or instrumentation, biofilm organisms could be shed into the urine and lead to ascending UTI and urosepsis. Novel developing technologies such as ureteral stents sonication offer a promising approach in the diagnosis of microbial ureteral stent colonization.11 Real-time polymerase chain reaction (PCR) detection of pathogens has also been studied to supplement conventional culture methods for the diagnosis of UTI. The main advantage of PCR is time saved in pathogen identification.12 The disadvantage of PCR is that they may have high sensitivity and thus lead to false-positive testing and cannot provide standardized susceptibility profiles.
Table 32-1 Diagnostic Criteria of CA-UTI, CA-ASB and ASB Without Indwelling Catheter in Adults
New onset or worsening of fever >38°C, rigors, altered mental status, malaise, or lethargy with no other identified cause; flank pain; costovertebral angle tenderness; acute hematuria; pelvic discomfort
In those whose catheters have been removed: dysuria, urgent or frequent urination, or suprapubic pain or tenderness
In patients with spinal cord injury: increased spasticity, autonomic dysreflexia, or sense of unease are also compatible with CA-UTI
103 units (CFU)/mL of more than one bacterial species in a single catheter urine specimen or in a midstream voided urine specimen from a patient whose urethral, suprapubic, or condom catheter has been removed within the previous 48 hours.
The absence of pyuria (urine specimen with >/=10 white blood cell mm3 or>/=3 WBC/high power field of unspun urine) in a symptomatic patient suggests a diagnosis other than CA-UTI.
105 CFU/mL of more than bacterial species in a single catheter urine specimen.
Man with a condom catheter is defined by the presence of 105 CFU/mL of one bacterial species in a single urine specimen from a freshly applied condom catheter.
Pyuria accompanying CA-ASB should not be interpreted as an indication for antimicrobial treatment.
