Improving statistical inference on pathogen densities estimated by quantitative molecular methods: malaria gametocytaemia as a case study

BACKGROUND: Quantitative molecular methods (QMMs) such as quantitative real-time polymerase chain reaction (q-PCR), reverse-transcriptase PCR (qRT-PCR) and quantitative nucleic acid sequence-based amplification (QT-NASBA) are increasingly used to estimate pathogen density in a variety of clinical and epidemiological contexts. These methods are often classified as semi-quantitative, yet estimates of reliability or sensitivity are seldom reported. Here, a statistical framework is developed for assessing the reliability (uncertainty) of pathogen densities estimated using QMMs and the associated diagnostic sensitivity. The method is illustrated with quantification of Plasmodium falciparum gametocytaemia by QT-NASBA. RESULTS: The reliability of pathogen (e.g. gametocyte) densities, and the accompanying diagnostic sensitivity, estimated by two contrasting statistical calibration techniques, are compared; a traditional method and a mixed model Bayesian approach. The latter accounts for statistical dependence of QMM assays run under identical laboratory protocols and permits structural modelling of experimental measurements, allowing precision to vary with pathogen density. Traditional calibration cannot account for inter-assay variability arising from imperfect QMMs and generates estimates of pathogen density that have poor reliability, are variable among assays and inaccurately reflect diagnostic sensitivity. The Bayesian mixed model approach assimilates information from replica QMM assays, improving reliability and inter-assay homogeneity, providing an accurate appraisal of quantitative and diagnostic performance. CONCLUSIONS: Bayesian mixed model statistical calibration supersedes traditional techniques in the context of QMM-derived estimates of pathogen density, offering the potential to improve substantially the depth and quality of clinical and epidemiological inference for a wide variety of pathogens

Effect of Preoperative Continuous Femoral Nerve Block in Ease of Administration of Spinal Anaesthesia for Fracture Neck of Femur Stabilisation: A Case-control Study

Introduction: Subarachnoid block remains the anaesthesia modality of choice for surgical fixation of femur. Extreme fracture pain makes ideal positioning for spinal anaesthesia difficult. Preoperative continuous femoral block can provide analgesia for such patients. Aim: To evaluate the effect of continuous femoral nerve block in ease of administration of spinal anaesthesia for fracture neck of femur stabilisation. Materials and Methods: This was a prospective case-control study conducted at the Government Medical College, Kozhikode, Kerala, India, from September 2020 to September 2021. Total of 86 adult patients posted for fracture femur neck stabilisation were selected and divided into two groups- group 1 and group 2. Patients in group 1, were administered ultrasound guided continuous femoral nerve block with 0.2% ropivacaine (15 mL) followed by subarachnoid block and group 2 patients were administered subarachnoid block without prior femoral nerve block. Parameters observed included were Visual Analogue Score (VAS) score while positioning for spinal anaesthesia, ease of palpating interspinous space, time required to perform spinal anaesthesia, number of attempts required to achieve dural puncture, patient satisfaction score as well as haemodynamic and respiratory changes while positioning for subarachnoid block. Statistical analysis was done using IBM SPSS (Statistical Package for the Social Sciences) Statistics for Windows, version 20.0. Results: Group 1 patients had significantly lower VAS scores while positioning for spinal anaesthesia (4.2±1.8 in group 1 as compared to 6.3±1.2 in group 2, p-value=0.001). There was a significant difference in the number of attempts required for dural puncture (1.3±0.4 in group 1 as compared to 1.8±0.6 in group 2, p-value=0.04) and total performance time for spinal anaesthesia (2.2±0.4 min in group 1 as compared to 3.3±0.9 minutes in group 2, p-value=0.02) between two groups. Patient satisfaction scores were significantly higher in group 1 compared to group 2 (9.3±0.6 in group 1 as compared to 6.5±0.5, p-value <0.001). Both groups were comparable in terms of ease of palpating inter spinous space, haemodynamic and respiratory changes during positioning for subarachnoid block. Conclusion: Preoperative administration of continuous femoral nerve block provides better conditions for performing subarachnoid block in fracture neck of femur surgeries by reducing the pain while positioning