Candida urinary tract infections--epidemiology.

Candiduria is rarely present in healthy individuals. In contrast, it is a common finding in hospitalized patients, especially those in intensive care units (ICUs) who often have multiple predisposing factors, including diabetes mellitus, indwelling urinary catheters, and exposure to antimicrobials. Candiduria occurs much less commonly in the community setting. In a majority of episodes in adult patients in critical care facilities candiduria represents colonization, and antifungal therapy is not required. However, the presence of yeast in the urine can be a sign of a disseminated infection. In the critically ill newborn, candiduria often reflects disseminated candidiasis and is accompanied by obstructing fungus ball formation in the urinary tract. In ICU patients, although candiduria is a marker for increased mortality, it is only rarely attributable to Candida urinary tract infection.

Candida urinary tract infection: pathogenesis.

Candida species are unusual causes of urinary tract infection (UTI) in healthy individuals, but common in the hospital setting or among patients with predisposing diseases and structural abnormalities of the kidney and collecting system. The urinary tract may be invaded in either an antegrade fashion from the bloodstream or retrograde via the urethra and bladder. Candida species employ a repertoire of virulence factors, including phenotypic switching, dimorphism, galvano - and thigmotropism, and hydrolytic enzymes, to colonize and then invade the urinary tract. Antegrade infection occurs primarily among patients predisposed to candidemia. The process of adherence to and invasion of the glomerulus, renal blood vessels, and renal tubules by Candida species was elegantly described in early histopathologic studies. Armed with modern molecular biologic techniques, the various virulence factors involved in bloodborne infection of the kidney are gradually being elucidated. Disturbances of urine flow, whether congenital or acquired, instrumentation of the urinary tract, diabetes mellitus, antimicrobial therapy, and immunosuppression underlie most instances of retrograde Candida UTI. In addition, bacterial UTIs caused by Enterobacteriaceae may facilitate the initial step in the process. Ascending infections generally do not result in candidemia in the absence of obstruction.

Candida urinary tract infections--diagnosis.

The finding of candiduria in a patient with or without symptoms should be neither dismissed nor hastily treated, but requires a careful evaluation, which should proceed in a logical fashion. Symptoms of Candida pyelonephritis, cystitis, prostatitis, or epididymo-orchitis are little different from those of the same infections produced by other pathogens. Candiduria occurring in critically ill patients should initially be regarded as a marker for the possibility of invasive candidiasis. The first step in evaluation is to verify funguria by repeating the urinalysis and urine culture. Pyuria is a nonspecific finding; the morphology of the offending yeast may allow separation of Candida glabrata from other species. Candida casts in the urine are indicative of renal candidiasis but are rarely seen. With respect to culture, colony counts have not proved to be diagnostically useful. In symptomatic or critically ill patients with candiduria, ultrasonography of the kidneys and collecting systems is the preferred initial study. However, computed tomography (CT) is better able to discern pyelonephritis or perinephric abscess. The role of magnetic resonance imaging and renal scintigraphy is ill defined, and prudent physicians should consult with colleagues in the departments of radiology and urology to determine the optimal studies in candiduric patients who require in-depth evaluation.

Candida urinary tract infections--treatment.

In many instances a report from the clinical laboratory indicating candiduria represents colonization or procurement contamination of the specimen and not invasive candidiasis. Even if infection of the urinary tract by Candida species can be confirmed, antifungal therapy is not always warranted. Further investigation may reveal predisposing factors, which if corrected or treated, result in the resolution of the infection. For those with symptomatic urinary tract infections (UTIs), the choice of antifungal agent will depend upon the clinical status of the patient, the site of infection, and the pharmacokinetics and pharmacodynamics of the agent. Because of its safety, achievement of high concentrations in the urine, and availability in both an oral and intravenous formulation, fluconazole is preferred for the treatment of Candida UTIs. Flucytosine is concentrated in urine and has broad activity against Candida spp, but its use requires caution because of toxicity. Low-dose amphotericin B may be useful for Candida UTIs in selected patients. The role of echinocandins and azoles that do not achieve measurable concentrations in the urine is not clear. Small case series note some success, but failures have also occurred. Irrigation of the bladder with antifungal agents has limited utility. However, with fungus balls, irrigation of the renal pelvis through a nephrostomy tube can be useful in combination with systemic antifungal agents.