Attributable hospital cost and antifungal treatment of invasive fungal diseases in high-risk hematology patients: an economic modeling approach.

Studies using patient-level data to determine the attributable cost of invasive fungal diseases (IFDs) are few. Using a case-control study with activity-based costing of patients admitted to a quaternary hospital from 2002 to 2007, we determined attributable hospitalization cost (and 12 weeks thereafter), length of stay (LOS), and costly antifungal treatment (C-AT; liposomal amphotericin B, voriconazole, posaconazole, caspofungin), expressed as defined daily doses (DDDs) per IFD episode, in patients with hematological malignancies and hematopoietic stem cell recipients. Matching criteria and median regression modeling controlled for confounding variables, including LOS prior to IFD onset. Multiple mycoses were identified in 43 matched case-control pairs (n=86). A separate sensitivity analysis included 22 unmatched patients. IFD status was associated with a median excess cost of AU$30,957 (95% confidence interval [CI]=AU$2,368 to AU$59,546; P=0.034), approximating at purchasing power parity US$21,203 (95% CI=US$1,622 to US$40,784) and €15,788 (95% CI=€1,208 to €30,368), increasing to AU$80,291 (95% CI=AU$33,636 to AU$126,946; P=0.001), i.e., US$54,993 (95% CI=US$23,038 to US$86,948) and €40,948 (95% CI=€17,154 to €64,742), with intensive care unit (ICU) requirement. Cost determinants were pharmacy costs (64%; P<0.001) inclusive of antifungal treatment (27%; P<0.001) and ward costs (27%; P=0.091), with proportions persisting through 12 weeks for 25 surviving matched pairs (pharmacy, 60% [P=0.12]; ward, 31% [P=0.21]). Median LOS was not significantly increased unless unmatched patients were included (8 days, 95% CI=1.8 to 14 days; P=0.012). Excess C-ATs were 17 DDDs (95% CI=15 to 19 DDDs; P<0.001) per case patient and 19 DDDs (95% CI=16 to 22 DDDs; P<0.001) per ICU patient. The sensitivity analysis was confirmatory (for median cost, AU$29,441, 95% CI=AU$5,571 to AU$53,310, P=0.016; for C-AT, 17 DDDs, 95% CI=16 to 18 DDDs, P<0.001). IFD results in increased hospital and ICU costs, with pharmacy costs, including antifungal treatment, being major determinants. Consumption of costly antifungal drugs may be a novel resource metric with wider generalizability than cost alone.