Impact of inappropriate antifungal therapy according to current susceptibility breakpoints on Candida bloodstream infection mortality, a retrospective analysis

Empirical therapy was defined as the initiation of an antifungal agent at the first clinical suspicion of fungal infection [11]. Initial antifungal therapy was defined as modification of the empirical antifungal therapy or initiation of any antifungal drug after a positive blood culture with yeasts on a Gram stain, before species identification; whereas definitive treatment was the antifungal administered after species identification. Severe sepsis was defined as the presence of sepsis with any of the following: sepsis-induced hypotension, hyperlactatemia, urine output < 5 ml/Kg/h for more than 2 h following fluid resuscitation, acute lung injury with PaO₂/FIO₂ < 250 or < 200 in the absence and presence of pneumonia, creatinine > 2 mg/dL, bilirubin > 2 mg/dL, platelet count < 100,000 cell/mm³ or coagulopathy [12].

Antifungal therapy was considered appropriate if the patient received an antifungal agent for which, the Candida isolate was susceptible according to CLSI 2012 breakpoints and inappropriate if the MIC of the isolate was in non-susceptible range [6, 13].

All the Candida spp. isolates recovered from blood cultures during the study period were sent to a central laboratory for identification and AST. The isolates were cultured on Sabouraud media, underwent germ tube testing and were identified using the Vitek 2, (BioMeriéux, Lyon, France). A sample from each culture was stored as water suspension at −80 °C, until retrieved for susceptibility testing. A small aliquote was unfrozen at room temperature for 24 h, and cultured on Sabouraud agar at 30 °C for 24 h to ensure viability. AST was performed on 178 available isolates of which 149 received antifungal treatment and were included for analysis. AST was performed with Vitek 2 using the AST-YS07 card (Biomérieux, Lyon, France) and interpreted according to CLSI guidelines in document M27A3 and its updated version in M27-S4. For those isolates without a species specific clinical breakpoint, epidemiologic cutoff values were used (C. guilliermondii, C. pelliculosa and Clavispora lusitaniae). For species without a reported epidemiological cut off value, AST was classified according to the Vitek-2 software (Global CLSI-based + Natural Resistance) (V. 07.01) [14‐16].

The reference strains C. parapsilosis ATCC 22019 and C. krusei ATCC 6258 were used as controls. Species identified as C. parapsilosis complex and C. glabrata complex refer to C. parapsilosis complex and C. glabrata complex, since phenotypic testing cannot differentiate the cryptic species within the complexes. Isolates were considered susceptible to echinocandins if the micafungin MIC was within the susceptible ranges, since anidulafungin is not available for YS07 card, and the known variability in the caspofungin MIC with Vitek2 [17, 18]. Assays to identify antifungal resistance mechanisms were not done.

Categorical data was summarized using frequency tables, and the χ² test was used for comparison between groups. Characteristics of patients were compared using Mann-Whitney U test for continuous variables. To evaluate 30-day mortality in multivariate analysis, we built a multiple logistic regression model including inappropriate antifungal treatment as well as variables with a p-value < 0.2 in univariate analysis or biological plausibility. Stratification for severe sepsis is provided in a separate analysis. Odds ratio (OR) with 95% confidence interval (CI) was reported. A p-value < 0.05 was considered significant for all the analysis. Stata 11.0 (Stata Corp College Station, TX) software was used for analysis.

The study was reviewed and approved by the Scientific and Bioethics Committee at the Instituto Nacional de Cancerología (reference number INCAN/005/10) and the Research and Bioethics Committee at the Instituto Nacional de Ciencias Médicas y Nutrición “Salvador Zubirán” (reference number 1912). Because of the observational nature of the study, a waiver of informed consent was granted. Authors involved in data analysis could not identify individual patients since the database used numbers specific to the study.

Blood cultures yielded a positive result for Candida spp. in a median of 2 days (IQR 1–3) after drawn. The most frequent isolated species were: C. albicans (n: 60, 40%), C. tropicalis (n: 34, 23%), C. glabrata complex (n: 30, 20%), C. parapsilosis complex (n: 15, 10%) and C. guilliermondi (n: 3, 2%). Other less frequent were: C. krusei (n: 2, 1.3%), C. norvegensis (n: 1, 0.6%), C. inconspicua (n: 1, 0.6%), C. lusitaniae (n:1, 0.6%) C. lipolytica (n: 1, 0.6%) and C. pelliculosa (n: 1, 0.6%).

According to the 2012 CLSI susceptibility breakpoints, 70% (104/149) of the isolates were susceptible to fluconazole, 95.3% (142/149) to caspofungin and, 97.3% (145/149) isolates to micafungin; and 98.6% (147/149) were susceptible to AmB (Table 2).

Overall fluconazole resistance was 6% (2 C. albicans, 2 C. glabrata complex, 2 C. kruzei, 1 C. parapsilosis complex, 1 C. tropicalis and 1 C. pelliculosa). Overall echinocandin resistance was 1.3% (1 C. albicans and 1 C. glabrata).

A single echinocandin-resistant C. glabrata was identified, which also was intermediate to fluconazole. One isolate of C. albicans showed resistance to every antifungal class (azoles, echinocandins and amphotericin B), from a patient who subsequently developed C. glabrata BSI secondary to a diabetic foot osteomyelitis in a 42-year-old male patient who died after 22 days of treatment with caspofungin.

Thirty-five of 149 patients (23%) were receiving antifungal therapy at the time the CBSI was identified, in 23/35 (66%) cases the indication was empiric therapy for suspected invasive fungal infection, 15/35 (42.8%) cases were receiving antifungal therapy for another demonstrated fungal infection; 18/35 (51.4%) patients received azoles (2 voriconazole and 16 fluconazole), 9/35 (25.7%) received AmB-d and 9/35 (25.7%) received echinocandins (3 caspofungin and 6 anidulafungin). In 7/35 (20%) cases, the CBSI agent was non-susceptible to empiric therapy.

Antifungal was initiated or modified within a median of two days (IQR 1–3) after the blood culture was drawn. Echinocandins were the most frequent initial treatment (42.9%), followed by amphotericin B-deoxycholate (AmB-d) (40.2%), and fluconazole (16.1%). One patient received combination therapy with AmB-d and fluconazole, and one received voriconazole. The initial antifungal agent was modified in 37% (55/149) of the episodes. Among these 47.3% (26/55) were switched to fluconazole after species identification. Twenty-three percent (13/55) were switched to other antifungal due lack of a clinical response; 12.7% (7/55) due to a nonsusceptible isolate (according to the known species-specific susceptibility); 5.4% (3/55) due to toxicity and 5.4% (3/55) due to proven or probable invasive aspergillosis; 3.6% (2/55) to treat other molds and 3.6% (2/55) due to unspecified reasons. Definitive antifungal treatment of 149 episodes was administered with echinocandins (37.5%), AmB-d (30.2%), and fluconazole (31.5%). One patient received a combination of AmB-d and fluconazole. Among the 89 non-albicans CBSI episodes, 41 (46%) received echinocandins as definitive treatment, 29 (32%) AmB-d, and 19 (21.3%) azoles. The median time of antifungal therapy was 14 days (IQR 5–20).

Regarding the CLSI 2012 breakpoints, 8.7% (13/149) patients received inappropriate initial antifungal treatment, four of which died: one patient received 12 days of fluconazole (6 mg/Kg) for a non-susceptible fluconazole C. albicans isolate, was switched later to caspofungin due lack of clinical response and died a day after. Two patients received fluconazole for susceptible dose-dependent (SDD) C. glabrata; one died five days after CBSI diagnosis, the other was switched to caspofungin on the sixth day and died. The remainder patient had a CBSI due to a fluconazole-resistant C. albicans isolate, the patient was started on fluconazole, was switched to caspofungin twelve days later and died 26 days after the CBSI diagnosis. Inappropriate definitive antifungal treatment was administered in 5.3% (8/149) of the episodes (5 C. glabrata, 2 C. albicans, and 1 C. tropicalis), two of which died: one patient received eight days of AmB-d, was switched to fluconazole for a fluconazole –SDD C. glabrata and died 22 days after diagnosis.

No patient received inappropriate initial or definitive treatment according to 2008 guidelines (Table 1).

Thirty-day mortality was 38% (56/149); non-survivors more often presented with severe sepsis and required mechanical ventilation. Non-survivors were also more likely to have hematologic neoplasia, cirrhosis, severe neutropenia and to receive definitive treatment with AmB-d. Survivors were more likely to have an intraabdominal infection, an early central-venous catheter removal, have received empirical antifungal therapy, to receive definitive treatment with azoles and to have a Non-albicans CBSI (Table 1). In multivariate analysis, severe sepsis (OR 3.4; 95% CI 1.3–8.4) and previous diagnosis of cirrhosis (OR 36 95% CI 12.2–605) were independently associated with increased 30-day mortality. Early CVC withdrawal (OR 0.23; 95% CI 0.08–0.66) and empirical antifungal therapy (OR 0.15; 95% CI 0.03–0.62) were independently associated with reduced 30-day mortality. When stratified by severe sepsis, survivors were more likely to receive empirical antifungal therapy (OR 0.05; 95% CI 0.005–0.55) and early CVC removal (OR 0.07; 95% CI 0.017–0.28) among patients without severe sepsis. Of note neither empirical antifungal therapy nor early CVC removal were associated with reduced mortality in patients with severe sepsis. Inappropriate initial or/and definitive antifungal treatment was not associated with 30-day mortality (OR 0.19; 95% CI 0.03–1.2), not even after stratification for severe sepsis (Table 3).