Departments of 1 Internal Medicine and 3 Laboratory Medicine, National Taiwan University Hospital No. 7, Chung-Shan South Road, Taipei; Departments of 2 Medicine and 4 Laboratory Medicine, College of Medicine, National Taiwan University, Taipei, Taiwan
Received 30 September 2002; returned 5 January 2003; revised 8 January 2003; accepted 2 April 2003
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Abstract |
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Keywords: Candida, nosocomial infection, antifungal susceptibility testing, outcome
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Introduction |
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Materials and methods |
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NTUH is a major teaching hospital in Taiwan. The number of beds increased from 1500 in 1994 to 2000 beds in 2000. Annual discharges were 45 358 in 1994 and 69 421 in 2000. Prospective, hospital-wide nosocomial infection surveillance was initiated in 1981. Data on nosocomial infections were collected, analysed and reported to the hospital infection control committee monthly and published annually.
Blood culture isolates
Blood samples were cultured by inoculation into BACTEC fungal medium (Becton-Dickinson Microbiology Systems, Cockeysville, MD, USA) and tested daily for microbial growth by a BACTEC 9240 system (BD Biosciences, Sparks, MD, USA). Organisms were identified by germ tube analysis and morphology on cornmeal-Tween 90 agar11 or, when necessary, by standard biochemical testing with the API 20C system (API bioMérieux Vitek, Inc., Hazelwood, MO, USA). Blood isolates of Candida species were collected weekly during 19942000. All the isolates were kept at 70°C and were subcultured at least twice on Sabouraud dextrose agar at 35°C before being tested. A total of 552 isolates were tested for susceptibility to fluconazole in this study.
Antifungal susceptibility testing
The MICs of fluconazole (Pfizer Pharmaceuticals, Inc., NY, USA) were determined by the disc diffusion method as part of the Global Antifungal Surveillance Program.12 This system uses a 25 µg fluconazole disc (Becton-Dickinson) and MuellerHinton agar supplemented with 2% glucose and 0.5 mg/L Methylene Blue. Inocula were adjusted to a 0.5 McFarland density standard. Plates were incubated aerobically at 35°C for 24 h and read by electronic image analysis and interpreted and recorded with a BIOMIC Plate Reader System (Giles Scientific Inc., Santa Barbara, CA, USA). Zone inhibition interpretive criteria for fluconazole disc testing were based on zone diameters correlated with NCCLS recommended category breakpoints for the reference macrobroth dilution method.13 Fluconazole breakpoints were: susceptible (≤8 mg/L or ≥19 mm), susceptible-dose-dependent (S-DD) (1632 mg/L or 1318 mm) and resistant (≥64 mg/L or ≤12 mm). Quality controls were carried out with each batch of clinical isolates by testing C. albicans ATCC 90028 with a recommended acceptable performance range of 3243 mm.
Data collection
All patients with nosocomial candidaemia diagnosed and treated at our hospital were observed prospectively until discharge or until death as part of the prospective nosocomial control programme.5,7 The incidence of nosocomial fungal infection and nosocomial candidaemia, the distribution of Candida species causing nosocomial candidaemia and annual consumption of antifungal agents were collected every year during 19812000. Data collected during 19811993 have been reported.5
Definitions
The Centers for Disease Control and Prevention definitions of nosocomial infections14 were used in order to include clinically significant, hospital-acquired infections and to exclude cultures containing contaminants or colonizing organisms. Candidaemia was defined when Candida species were isolated from blood culture(s) collected from a patient with signs and symptoms of infection. Candidaemia was considered to be the primary cause of death of patients who died within 7 days following a positive blood culture, when no other cause (including the primary disease, other infections and haemorrhage) was identified.7 Candidaemia was considered to be an associated cause of death when it was still present at time of death (as indicated by fever, with or without positive cultures), although another complication (e.g. haemorrhage or a secondary non-fungal infection) or an uncontrolled underlying disease was also present. Attributable mortality included both. Death was considered unrelated to candidaemia when candidaemia was cleared at time of death (by symptoms, signs and blood culture) and there was another likely cause such as the underlying disease.
Statistical analyses
Statistical analyses were carried out with the Statistical Package for the Social Sciences (SPSS, version 10.0) for Windows (SPSS Inc., Chicago, IL, USA). Univariate analysis of categorical variables was done with the 2 test or Fishers exact test. Continuous variables were analysed by the Students t-test. All P values were two-tailed, and a P value <0.05 was considered to indicate statistical significance.
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Results |
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The incidence of nosocomial fungal infections increased gradually from 1981 to 2000 (Figure 1). Nosocomial candidaemia increased rapidly during 19811996. There was no significant change in the incidence of nosocomial candidaemia during 19962000. Candida species were the leading cause of nosocomial bloodstream infection (including both primary and secondary) during 19931999, and were second only to Staphylococcus aureus in 2000 (2.8 and 3.6 episodes per 1000 discharges, respectively). Annual consumption of fluconazole (both parenteral and oral forms) increased gradually from 0.08 g per 1000 patient days in 1991 to 9.82 g per 1000 patient days in 2000 (Figure 2a). The trends for other antifungal drugs are shown in Figure 2(b).
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During 19942000, a total of 1095 episodes of nosocomial candidaemia occurred. C. albicans was the leading species (50.4%), followed by Candida tropicalis (20.5%), Candida parapsilosis (14.2%) and Candida glabrata (12.0%). There were only six episodes of Candida krusei during the 7 year period. The proportion of non-albicans Candida species reached its peak in 1996 (62.5%) and did not change significantly thereafter (51.1% in 2000) (Figure 3). Parallel to this trend, the proportion of C. glabrata increased gradually to 19.4% in 1996 and decreased thereafter to 9.0% in 2000.
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The MICs of fluconazole were determined for 552 Candida blood isolates. This included 188 isolates of C. albicans, 155 isolates of C. parapsilosis, 116 isolates of C. tropicalis, 85 isolates of C. glabrata and eight isolates of Candida guillermondii. Fluconazole susceptibility was 94.0% in 19941995 and 97.9% in 19992000 (P = 0.06) (Table 2). The proportion of fluconazole-resistant strains was low (0.7%) and did not change significantly during the study period for any species (Table 2). The frequency of resistant or dose-dependent susceptible strains was greater for C. glabrata (5.9%) and C. tropicalis (7.7%) than C. albicans (2.1%) and C. parapsilosis (1.3%) (P = 0.016).
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Out of 188 patients with nosocomial candidaemia in 2000, 65 (34.6%) died within 14 days from the onset of candidaemia and 81 (43.1%) died within 30 days. The overall mortality at discharge was 60.6% (114/188). This was similar to mortality observed during 19941995 (59.3%, 70/118)7 (P > 0.05). Attributable mortality in 2000 was 25% (47/188). This was lower than that of 19941995 (43.2%, 51/118)7 (P = 0.005).
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Discussion |
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Despite these fears, the current study at NTUH demonstrates that the percentage of fluconazole-resistant blood isolates remains quite low, and did not appear to be increasing despite increased use of fluconazole. This trend appears to be due in part to a decrease in C. glabrata and increase in fluconazole susceptibility in C. tropicalis. A possible explanation for these findings is that we were able to decrease cross-resistance to fluconazole by restricting the use of other azoles such as ketoconazole and itraconazole.1517 The decrease in the proportion of C. glabrata from 19% in 1996 to 9% in 2000 at NTHU differs from reports from Europe,23,25 Canada23,24 and the USA22,23,26 (Table 3). Furthermore, the proportion of fluconazole-susceptible Candida species of 97.9% at our hospital during 19992000 was greater than reported elsewhere (Table 4).12,2224,2730 We doubt that these differences can be accounted for by methods in fluconazole susceptibility testing since we used the Global Antifungal Surveillance Group disc diffusion method,12 which has been shown to generate the same results as the broth microdilution method.23,28,29,31
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When comparing data collected in different geographical regions (Table 3), the percentage of C. tropicalis was higher at NTUH (23%) and in Argentina (20%)37 than in other countries. Our previous study showed that C. tropicalis was more frequently isolated from patients with neutropenia than those without.7 Abi-Said et al.21 suggested the absence of fluconazole prophylaxis as an independent predictor of C. tropicalis fungaemia in patients with cancer. At our hospital, fluconazole was not used for prophylaxis except in bone marrow transplant recipients. This might be the reason that C. tropicalis was the second most common species of Candida causing fungaemia at NTUH (Figure 3). On the other hand, the impact of geographical variation and/or environmental sources was unknown. Furthermore, the incidence of S-DD isolates was relatively high. Only 86.1% of C. tropicalis collected during 19961997 were susceptible to fluconazole and 100% during 19992000. This unique trend could not be explained by the contribution of fluconazole use alone34,38 and is possibly due to a decrease in the use of other azoles.
The present study had several limitations.39 First, the impact of use of antibacterial drugs on the emergence of nosocomial candidaemia was not included in this study. Secondly, we are unable to assess the effect of the recent restriction of over-the-counter sales of azoles in Taiwan. Thirdly, we did not conduct a formal study of prescribing practices of fluconazole at NTUH to confirm that our recommendations were implemented. Fourthly, these findings are limited to the experience of a single centre study. Nevertheless NTUH is very similar to other major medical centres in that it has a heavy concentration of immunocompromised patients and clustered critically ill patients6,7 and a high prevalence of antibacterial resistance.8,9 Furthermore, the disc method does not do well in distinguishing susceptible from S-DD categories and may contribute to the discrepancy between the proportions of C. tropicalis in the S-DD category during 19941995 using the disc method or broth microdilution method (12.1% and 0%, respectively) (Table 4).
Global trends in fluconazole resistance to Candida species make it increasingly more important to select antifungal agents for empirical use based on ongoing surveillance of local patterns of the prevalence of the various Candida species and their susceptibility to antifungal drugs.40 The rational use of antifungal drugs will become even more important as new agents are introduced. Furthermore, comparison between different antifungal agents, using resistance as an endpoint in addition to patient outcome, may reveal how to avoid losing the azoles as promising antifungal agents.4143
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Acknowledgements |
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Footnotes |
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References |
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