Quantitative urine cultures do not reliably detect renal candidiasis in rabbits

Abstract

The significance of quantitative urine cultures in patients at risk for hematogenous disseminated candidiasis is controversial. While various concentrations of Candida spp. in urine have been suggested as critical cutoff points in the diagnosis of renal candidiasis, other investigators consider quantitative cultures less critical in diagnosing upper tract infections. To determine the significance of quantitative urine cultures in renal candidiasis, we studied serial quantitative urinary cultures of Candida albicans in a rabbit model of hematogenous infection. Of 197 urine samples from 34 infected animals, 144 were culture positive, with a sensitivity of 73.1% for urine cultures and a lower limit of detection of 10 CFU/ml. The yield of urine cultures varied according to severity and duration of infection. The mean renal and urinary concentrations of C. albicans from rabbits with subacute candidiasis differed significantly from those from rabbits with acute candidiasis (P ‫؍‬ 0.013 and P < 0.001, respectively). During the first 4 days of subacute renal candidiasis, more than one-half of all urine cultures were negative for C. albicans. Only 12 (8.1%) of 148 urine cultures in animals with subacute renal candidiasis had concentrations of >10 3 CFU/ml, 2.7% had concentrations of >10 4 CFU/ml, and none were >10 5 CFU/ml. By comparison, all urine cultures from the animals with lethal acute renal candidiasis had higher concentrations of C. albicans and were positive throughout the course of infection. Urinary concentrations of C. albicans were not predictive of the amount of Candida in the kidney (r < 0.49) and did not correlate with survival (r ‫؍‬ 0.0232). However, the renal concentration of C. albicans (in CFU/gram) inversely correlated with the duration of survival (in days) of rabbits with renal candidiasis (r ‫؍‬ 0.76; P < 0.001). These findings indicate that a negative urine culture in rabbits does not preclude the presence of renal candidiasis. The interpretation of a urine culture positive at any concentration, on the other hand, must involve an analysis of the risk factors for renal candidiasis, for any urinary concentration of C. albicans may reflect kidney infection.

To treat or not to treat – critically ill patients with candiduria

“…in the urine could reflect renal involvement. 46 Furthermore, blood cultures have approximately 40-75% false-negative results and may take 3-4 days for definitive results, and autopsy studies have taught us that negative blood cultures and tissue biopsies have been obtained in more than 50% of disseminated fungal infection. 38,55 Therefore, sensitive and specific parameters are needed for detection of fungal UTI, aside from the necessity to diagnose IC.…”

“…In fact, data obtained from experimental animal systems of haematogenous renal candidiasis proved that any concentration of Candida spp. in the urine could reflect renal involvement 46 . Furthermore, blood cultures have approximately 40–75% false‐negative results and may take 3–4 days for definitive results, and autopsy studies have taught us that negative blood cultures and tissue biopsies have been obtained in more than 50% of disseminated fungal infection 38,55 .…”