Antifungal susceptibility testing and the correlation with clinical outcome in neonatal candidemia

Antifungal Susceptibility and Clinical Outcome in Neonatal Candidiasis

BACKGROUND

Invasive candidiasis is an important cause of sepsis in extremely low birth weight infants (ELBW, < 1000 g), is often fatal, and frequently results in neurodevelopmental impairment (NDI) among survivors. We sought to assess the antifungal minimum inhibitory concentration (MIC) distribution for Candida in ELBW infants and evaluate the association between antifungal resistance and death or NDI.

METHODS

This was a secondary analysis of a National Institute of Child Health and Human Development Neonatal Research Network study. MIC values were determined for fluconazole, amphotericin B and micafungin. NDI was assessed at 18-22 months adjusted age using the Bayley Scales of Infant Development. An infant was defined as having a resistant Candida isolate if ≥ 1 positive cultures from normally sterile sites (blood, cerebrospinal fluid, or urine) were resistant to ≥ 1 antifungal agent. In addition to resistance status, we categorized fungal isolates according to MIC values (low and high). The association between death/NDI and MIC level was determined using logistic regression, controlling for gestational age and Bayley Scales of Infant Development (II or III).

RESULTS

Among 137 ELBW infants with IC, MICs were determined for 308 isolates from 110 (80%) infants. Three Candida isolates from 3 infants were resistant to fluconazole. None were resistant to amphotericin B or micafungin. No significant difference in death, NDI, or death/NDI between groups with low and high MICs was observed.

CONCLUSIONS

Antifungal resistance was rare among infecting Candida isolates, and MIC level was not associated with increased risk of death or NDI in this cohort of ELBW infants.

Old Cryptococcus neoformans cells contribute to virulence in chronic cryptococcosis

Does cell age matter in virulence? The emergence of persister cells during chronic infections is critical for persistence of infection, but little is known how this occurs. Here, we demonstrate for the first time that the replicative age of the fungal pathogen Cryptococcus neoformans contributes to persistence during chronic meningoencephalitis. Generationally older C. neoformans cells are more resistant to hydrogen peroxide stress, macrophage intracellular killing, and antifungal agents. Older cells accumulate in both experimental rat infection and in human cryptococcosis. Mathematical modeling supports the concept that the presence of older C. neoformans cells emerges from in vivo selection pressures. We propose that advanced replicative aging is a new unanticipated virulence trait that emerges during chronic fungal infection and facilitates persistence. Therapeutic interventions that target old cells could help in the clearance of chronic infections.

Our findings that the generational age of Cryptococcus neoformans cells matters in pathogenesis introduces a novel concept to eukaryotic pathogenesis research. We propose that emerging properties of aging C. neoformans cells and possibly also other fungal pathogens contribute to persistence and virulence. Whereas the replicative life span of strains may not matter for virulence per se, age-related resilience and thus the generational age of individual C. neoformans cells within a pathogen population could greatly affect persistence of the pathogen population and therefore impact outcome.

Epidemiology of candidemia at a Children's hospital, 2002 to 2006

BACKGROUND

There are few recent studies evaluating trends in the epidemiology of candidemia including changes in species or utilization of antifungal agents in children.

METHODS

We performed a retrospective case series of candidemia at our children's hospital from 2002 to 2006. Our objectives were to study trends in the rates of candidemia, demographic characteristics, Candida species, antifungal susceptibility, and antifungal utilization. These data were obtained from the electronic medical records.

RESULTS

There were 203 episodes of candidemia in 154 subjects. During the study period, the average rate of candidemia was 5.52 per 1000 patient-discharges and did not change throughout the study. The mean and median ages of subjects were 3 years versus 9 months, respectively, and 38% were less than 3 months of age. Gastrointestinal disorders were a common comorbid condition (33%), especially for subjects with multiple episodes of candidemia. Overall, Candida parapsilosis and Candida albicans caused 43% and 26% of episodes, respectively, and candidemia caused by Candida glabrata (5.3%-23%) and Candida krusei (0%-8.5%) increased during the study. Ninety-eight percent of C. albicans and C. parapsilosis isolates remained susceptible to all antifungal drugs. From 2003-2006, the use of antifungal agents increased from 79 days to 150 days per 1000 hospital-days.

CONCLUSIONS

While antifungal use at our hospital increased, candidemia rates remained stable. C. parapsilosis was the most common species but other non-C. albicans species increased during the study period. Local epidemiology should be monitored in pediatric populations for potential impact on management strategies.

Fluconazole dosing for the prevention or treatment of invasive candidiasis in young infants

BACKGROUND

Young infants are susceptible to developmental factors influencing the pharmacokinetics of drugs. Fluconazole is increasingly used to prevent and treat invasive candidiasis in infants. Dosing guidance remains empiric and variable because limited pharmacokinetic data exist.

METHODS

Our population pharmacokinetic model derived from 357 fluconazole plasma concentrations from 55 infants (23-40 week gestation) illustrates expected changes in fluconazole clearance based upon gestational age, postnatal age, weight, and creatinine. We used a Monte Carlo simulation approach based on parametric description of a patient population's pharmacokinetic response to fluconazole to predict fluconazole exposure (median: 10th and 90th percentile population variability range) after 3, 6, and 12 mg/kg dosing.

RESULTS

For the treatment of invasive candidiasis, a dose of at least 12 mg/kg/d in the first 90 days after birth is needed to achieve an area under the concentration curve (AUC) of >400 mg*h/L and an AUC/minimum inhibitory concentration (MIC) >50 for Candida species with MIC <8 microg/mL in > or =90% of <30 week gestation infants and 80% of 30 to 40 week gestation infants. The more preterm infants achieve a higher median AUC (682 mg*hr/L) compared with more mature infants (520 mg*hr/L). For early prevention of candidiasis in 23 to 29 week infants, a dose of 3 or 6 mg/kg twice weekly during the first 42 days of life is equivalent to an AUC of 50 and 100 mg*hr/L, respectively, and maintains fluconazole concentrations > or =2 or 4 microg/mL, respectively, for half of the dosing interval. For late prevention, the 6 mg/kg dose every 72 hours provides similar exposure to 3 mg/kg daily dose. Infants with serum creatinine > or =1.3 mg/dL have delayed drug clearance and dose adjustment is indicated if creatinine does not improve within 96 hours.

CONCLUSIONS

A therapeutic concentration of fluconazole in premature infants with invasive candidiasis requires dosing substantially greater than commonly recommended in most reference texts. To prevent invasive candidiasis, twice weekly prophylaxis regimens can provide adequate exposure when unit specific MICs are taken into account.

Current status of antifungal susceptibility testing methods

Antifungal susceptibility testing is a very dynamic field of medical mycology. Standardization of in vitro susceptibility tests by the Clinical and Laboratory Standards Institute (CLSI) and the European Committee for Antimicrobial Susceptibility Testing (EUCAST), and current availability of reference methods constituted the major remarkable steps in the field. Based on the established minimum inhibitory concentration (MIC) breakpoints, it is now possible to determine the susceptibilities of Candida strains to fluconazole, itraconazole, voriconazole, and flucytosine. Moreover, utility of fluconazole antifungal susceptibility tests as an adjunct in optimizing treatment of candidiasis has now been validated. While the MIC breakpoints and clinical significance of susceptibility testing for the remaining fungi and antifungal drugs remain yet unclear, modifications of the available methods as well as other methodologies are being intensively studied to overcome the present drawbacks and limitations. Among the other methods under investigation are Etest, colorimetric microdilution, agar dilution, determination of fungicidal activity, flow cytometry, and ergosterol quantitation. Etest offers the advantage of practical application and favorable agreement rates with the reference methods that are frequently above acceptable limits. However, MIC breakpoints for Etest remain to be evaluated and established. Development of commercially available, standardized colorimetric panels that are based on CLSI method parameters has added more to the antifungal susceptibility testing armamentarium. Flow cytometry, on the other hand, appears to offer rapid susceptibility testing but requires specified equipment and further evaluation for reproducibility and standardization. Ergosterol quantitation is another novel approach, which appears potentially beneficial particularly in discrimination of azole-resistant isolates from heavy trailers. The method is yet investigational and requires to be further studied. Developments in methodology and applications of antifungal susceptibility testing will hopefully provide enhanced utility in clinical guidance of antifungal therapy. However, and particularly in immunosuppressed host, in vitro susceptibility is and will remain only one of several factors that influence clinical outcome.

Antifungal agents in neonates: issues and recommendations

Fungal infections are responsible for considerable morbidity and mortality in the neonatal period, particularly among premature neonates. Four classes of antifungal agents are commonly used in the treatment of fungal infections in pediatric patients: polyene macrolides, fluorinated pyrimidines, triazoles, and echinocandins. Due to the paucity of pediatric data, many recommendations for the use of antifungal agents in this population are derived from the experience in adults. The purpose of this article was to review the published data on fungal infections and antifungal agents, with a focus on neonatal patients, and to provide an overview of the differences in antifungal pharmacology in neonates compared with adults. Pharmacokinetic data suggest dosing differences in children versus adult patients with some antifungals, but not all agents have been fully evaluated. The available pharmacokinetic data on the amphotericin B deoxycholate formulation in neonates exhibit considerable variability; nevertheless, the dosage regimen suggested in the neonatal population is similar to that used in adults. More pharmacokinetic information is available on the liposomal and lipid complex preparations of amphotericin B and fluconazole, and it supports their use in neonates; however, the optimal dosage and duration of therapy is difficult to establish. All amphotericin-B formulations, frequently used in combination with flucytosine, are useful for treating disseminated fungal infections and Candida meningitis in neonates. Fluconazole, with potent in vitro activity against Cryptococcus neoformans and almost all Candida spp., has been used in neonates with invasive candidiasis at dosages of 6 mg/kg/day, and for antifungal prophylaxis in high-risk neonates. There are limited data on itraconazole, voriconazole, and posaconazole use in neonates. Caspofungin, which is active against Candida spp. and Aspergillus spp., requires higher doses in children relative to adults, and dosing is best accomplished based on body surface area. Micafungin shows a clear trend toward lower levels in the smallest patients. There are no data on the use of other new antifungal drugs (ravuconazole and anidulafungin) in neonates. In summary, the initial data suggest dosage differences in neonates for some antifungal agents, although the newer agents have not been fully tested for optimal administration in these patients.

Fluconazole and Itraconazole Resistance of Yeasts Isolated from the Bloodstream and Catheters of Hospitalized Pediatric Patients

BACKGROUND

In critically ill children, Candida species and other yeasts appear as an important nosocomial pathogen. The emerging fungal pathogens are usually less susceptible to azole compounds, and the management of such infections could be problematic.

METHODS

6,065 bloodstream cultures and 627 catheters from intensive care units and hospitalized oncology pediatric patients were studied. Antifungal susceptibility testing of isolates was performed according to the reference broth microdilution method describedby the National Committee for Clinical Laboratory Standards (M27-A).

RESULTS

We found a low activity of fluconazole (FCZ) and itraconazole (ITZ) against Candida glabrata, C. albicans, C. tropicalis and C. haemulonii. Resistant strains to FCZ and ITZ were detected.

CONCLUSION

Results reveal the emergence of antifungal-resistant species and a change in the predominant role of C. albicans as a cause of candidemia in hospitalized children.

Etiology of fungaemia and catheter colonisation in Argentinean paediatric patients

Yeast strains obtained from blood cultures and catheters from intensive care units (ICU) and hospitalised oncology paediatrics were studied. Yeast were the first cause of catheter colonisation (51/627), and the third cause of bloodstream infection (44/6065). In catheter, the most frequent species were Candida albicans (34%), C. parapsilosis (27.7%) and C. tropicalis (15%). In blood, C. albicans (40.8%), C. parapsilosis (26.6%), C. tropicalis (15%). Malassezia furfur and Malassezia sympodialis were isolated from catheters from ICU patients. All isolates were susceptible to amphotericin B, 88.8% to itraconazole and 91.9% to fluconazole. Candida albicans and C. tropicalis strains resistant to fluconazole and itraconazol were detected. These results reveal a change in the predominant role of C. albicans as cause of candidemia in hospitalised children and the emergence of antifungal resistant species. These variations emphasise the importance of performing a permanent surveillance to observe and assess them.

Azole resistance in neonatal intensive care units in Argentina

The aim of this study was to determine the antifungal susceptibility profile and to detect resistant strains of yeast species isolated from neonates in Intensive Care Units. 92 strains isolated from 25 bloodstream cultures, 20 venous catheters, 23 suprapubic aspirations and 24 rectal swabs were studied. A Candida glabrata strain resistant to fluconazole was detected. Candida krusei appeared with its inherent resistance to fluconazole and showed cross-resistance to itraconazole. Two Candida albicans strains were resistant to azoles, one to itraconazole and the other to fluconazole with a high minimum inhibitory concentration (MIC) for itraconazole. All Candida tropicalis strains were susceptible to fluconazole but two of them showed resistance to itraconazole. The detection of resistant strains in neonates whom had not received previous antifungal therapy is noteworthy. The variations in the epidemiology of fungal infections observed and the antifungal resistance detected emphasize the importance of performing a regular surveillance to observe and to assess them.

Neonatal candidiasis: analysis of epidemiology, drug susceptibility, and molecular typing of causative isolates

A prospective observational study of invasive candidiasis was conducted in the neonatal intensive care unit of Aristotle University in Hippokration Hospital between 1994 and 2000. During this period, 59 neonates developed invasive candidiasis (58 cases of candidemia and 1 case of peritonitis), resulting in an overall incidence of 1.28% that showed a decreasing trend over the study period. Eleven (18.6%) cases developed within the first week of life and the others within a mean (+/-SEM) of 13.4+/-1.7 days after birth. The three most frequent causative species were Candida albicans (65.5%), Candida parapsilosis (15.5%), and Candida tropicalis (7%). C. albicans was the predominant species between 1994 and 1998, whereas, non-albicans Candida spp., particularly C. parapsilosis, were the most frequent species during the period 1999-2000 (P<0.001). While the overall mortality due to candidemia was 29% (17 of 59 cases), mortality associated with C. albicans and C. parapsilosis was 39.5% and 11.1%, respectively (P=0.032), and that observed in the 1999-2000 period was 0% (P=0.011). Virtually all isolates were susceptible to amphotericin B, flucytosine, fluconazole, and itraconazole, and no increases in minimal inhibitory concentrations were observed during these years. With the exception of a limited cluster of cases due to genotypically identical isolates, no clonal relation of C. albicans isolates was found. Moreover, no clonal persistence of C. albicans and no decrease in antifungal drug susceptibility occurred over the 6-year study period. Non-albicans Candida spp., mostly C. parapsilosis, have emerged as important pathogens in neonatal intensive care units, with infected patients having better outcomes as compared to patients infected with C. albicans.

Yeasts species distribution in Neonatal Intensive Care Units in northeast Argentina. Das Hefeartenspektrum in Neugeborenen-Intensivstationen in Nordost-Argentinien

The aim of this study was to determine the distribution and antifungal susceptibility profile of yeast species isolated from neonates in Neonatal Intensive Care Units (NICU) in northeast of Argentina. With this purpose 92 strains isolated from 25 blood stream cultures, 20 venous catheters, 23 suprapubic aspirations and 24 rectal swabs were studied. Candida albicans and C. parapsilosis appeared with similar frequencies (36%) in blood stream isolates. Candida parapsilosis (50%) was the most frequent catheters colonizer and C. tropicalis (54.2%) was the most frequent yeast associated with gastrointestinal tract colonization. Candida krusei, C. glabrata and Trichosporon cutaneum appeared with a very low frequency. A high rate of susceptibility to amphotericin B, fluconazole, and itraconazole was observed.

Antifungals in systemic neonatal candidiasis

Fungal infections are common in the newborn period, especially among premature neonates, and are responsible for considerable morbidity and mortality. Currently, three classes of antifungals are commonly used in the treatment of systemic fungal infections in neonates: the polyene macrolides (e.g. amphotericin B [deoxycholate and lipid preparations]); the azoles (e.g. fluconazole); and the fluorinated pyrimidines (e.g. flucytosine). The echinocandins (e.g. caspofungin and micafungin) are a newer class of antifungals which shows promise in this population.The available kinetic data on amphotericin B deoxycholate in neonates are derived from very small studies and exhibit considerable variability. There are no kinetic data available for the use of lipid preparations in this population and, again, much has been inferred from adult studies. The information available for flucytosine is also limited but appears similar to what is observed in adults. Fluconazole has the most neonatal pharmacokinetic data, which show slightly less variability than the other antifungals. Genomic factors which affect the metabolism of amphotericin B and fluconazole may explain some of the observed variability. Most of the data for the efficacy of antifungal drugs in neonates are derived from retrospective studies and case reports. The data for amphotericin B deoxycholate and flucytosine are limited. There are more data for the liposomal and lipid complex preparations of amphotericin B and for fluconazole in this population. These support the use of these drugs in neonates, but because of their largely noncomparative nature they can not define the optimal dosage or duration of therapy. Amphotericin B deoxycholate is primarily nephrotoxic. It also induces electrolyte abnormalities and is to a lesser degree cardiotoxic. This toxicity in neonates appears similar to published data in older children and adults. While the lipid preparations of amphotericin B owe their existence to a presumed decrease in toxicity, the observed toxicity in neonates appears to be equal to that seen with the deoxycholate, although it should be noted that the lipid preparations are usually given at much higher dosages. Fluconazole toxicity appears to be milder and less frequent in this population than is seen with amphotericin B. In the final analysis, we do not have sufficient data to define the pharmacokinetic profiles, optimal dose or duration of therapy, or toxicity for any of these compounds in neonates. Further studies are necessary if the optimisation of antifungal therapy in this population is to continue.

Clinical impact of the fungicidal activity of caspofungin administered alone or in combination in critically ill patients with severe abdominal candidiasis refractory to conventional antifungal drugs: case studies and critical review of the problem

We discuss two cases of abdominal candidiasis in critically ill patients with multiple organ failure and sepsis. Microbiological and clinical courses remained unresponsive to apparently appropriate antifungal therapy with azole or polyene derivatives. Both microbiological and clinical outcomes dramatically improved after starting caspofungin therapy. Lack of cross-resistance, lack of toxicity and potent fungicidal activity make caspofungin a very attractive drug in life threatening abdominal candidiasis. The optimal treatment of life threatening candidiasis remains a controversial issue. Because of recent advances in the field, we propose a critical review of the problem of refractory candidiasis.

Strategies for prevention of neonatal invasive candidiasis

A single-center randomized, placebo-controlled trial has found that intravenous fluconazole prophylaxis in preterm infants < or = 1,000 g with a central venous catheter or endotracheal tube until such infants no longer required intravenous access or attained 6 weeks postnatal age was effective in preventing fungal sepsis. Infants at high risk for fungal sepsis are preterm infants < or = 32 weeks' gestation with one or more of the following additional risk factors: receipt of more than 2 antibiotics, third-generation cephalosporins, histamine-2 receptor antagonists, postnatal steroids, parenteral nutrition, or intravenous lipids; central venous catheter, skin disruption, dermatitis, necrotizing enterocolitis, or abdominal surgery. Further study in larger populations is needed to explore whether antifungal chemoprophylaxis or other strategies may be effective in preventing fungal infection in high-risk neonates. Effective prophylaxis strategies will decrease the high mortality and morbidity associated with fungal infection in high risk infants.