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An immunosensor for the detection of Listeria monocytogenes was developed. ELISA and amperometric studies were run in parallel to develop a more sensitive and rapid assay for the bacterium. Conditions for the immunosensor were primarily characterised using ELISA. A direct sandwich assay was employed and the affinities of two polyclonal (goat and rabbit) and one monoclonal (mouse) anti-L. monocytogenes antibodies were compared using this format. Owing to low sensitivity being obtained with all antibodies, biotin–avidin amplification and an indirect sandwich assay were employed. The system was then transferred to screen-printed electrodes (SPEs), the primary antibody being immobilised by cross-linking with 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide, and the mode of detection being amperometric. Various parameters (limit of detection, working range, incubation time, cross-reactivity) of the systems were characterised. The effect of direct incubation in milk is also discussed. The final immunosensor had a working range of 1 × 106–1 × 103 cells ml–1 and a detection limit of 9 × 102 cells ml–1. The assay took about 3.5 h to complete.

INTRODUCTION: Posaconazole prophylaxis in high-risk neutropenic patients prevents invasive fungal infection (IFI). An economic model was used to assess the cost effectiveness of posaconazole from a Canadian health care system perspective.METHODS: A decision-analytic model was developed based on data from a randomized trial comparing posaconazole with standard azole (fluconazole or itraconazole) therapy. The model was extrapolated to a lifetime horizon using one-month Markov cycles; lifetime survival was specific to the underlying disease. Drug and treatment costs associated with IFI were estimated using published literature. The model was used to estimate total costs, IFIs avoided, life-years gained and the incremental cost-effectiveness ratio of posaconazole versus standard azole therapy, in 2007 Canadian dollars.RESULTS: Based on the clinical trial data, posaconazole was associated with fewer cases of IFI (0.05 versus 0.11; P=0.003), increased life-years (2.52 years versus 2.43 years) and slightly lower costs ($6,601 versus $7,045) per patient relative to standard azole therapy over a lifetime horizon. Higher acquisition costs for posaconazole were offset by IFI-associated inpatient costs for those prophylaxed with standard azoles. Probabilistic sensitivity analysis indicated a 59% probability that posaconazole was cost-saving versus standard azole therapy and a 96% probability that the incremental cost-effectiveness ratio for posaconazole was at or below the $50,000 per life-year saved threshold.DISCUSSION: In Canada, posaconazole appears to be cost-saving relative to standard azole therapy in IFI prevention among high-risk neutropenic patients.