1,721,062 research outputs found
Is there information after death?. In Discussion of Farrington CP and Whitaker HJ "Semiparametric analysis of case series data"
No full textEstimation in emerging epidemics: biases and remedies.
No full textWhen analysing new emerging infectious disease outbreaks, one typically has observational data over a limited period of time and several parameters to estimate, such as growth rate, the basic reproduction number R-0, the case fatality rate and distributions of serial intervals, generation times, latency and incubation times and times between onset of symptoms, notification, death and recovery/discharge. These parameters form the basis for predicting a future outbreak, planning preventive measures and monitoring the progress of the disease outbreak. We study inference problems during the emerging phase of an outbreak, and point out potential sources of bias, with emphasis on: contact tracing backwards in time, replacing generation times by serial intervals, multiple potential infectors and censoring effects amplified by exponential growth. These biases directly affect the estimation of, for example, the generation time distribution and the case fatality rate, but can then propagate to other estimates such as R-0 and growth rate. We propose methods to remove or at least reduce bias using statistical modelling. We illustrate the theory by numerical examples and simulations.</p
A simple explanation for the low impact of border control as a countermeasure to the spread of an infectious disease
No full textA simple model for the effect of border control or travel restrictions is proposed. It can be used to predict the corresponding results in quite complex disease spread models and has the advantage of providing easy qualitative understanding of the effects of this kind of intervention
Quantifying the re-exposure process to an infectious agent. Measles and varicella as examples
No full textBACKGROUND AND OBJECTIVES: For viral infections conferring what is usually considered as permanent immunity, re-exposure to the pathogen due to contacts with infectious individuals might be critical for immunity boosting. A major example is represented by the varicella-zoster virus (VZV) where re-exposure is thought to lead to boosting of cell mediated immunity (CMI), which plays a protective role against the development of herpes zoster (HZ). Similar concerns have recently been raised also in relation to measles. However, while the first effective exposure, i.e. infection, has been the object of many studies, both theoretical and epidemiological, there has been no corresponding investigation of the re-exposure process.; METHODOLOGY AND DATA: By combining basic concepts from deterministic and stochastic modelling of infection, we develop a basic model for quantifying the timing and number of re-exposures and, consequently, the potential for immune boosting at any given age. The model is then applied to measles, mumps and rubella (MMR) in the UK, and to varicella in Italy, using literature estimates of the pre-vaccination forces of infection.; RESULTS: We supply analytical expressions for the expected number of lifetime re-exposures and for underlying age-patterns, including the average age at which the last re-exposure occurs. Based on updated estimates of the force of VZV infection, we show that the expected number of boosting opportunities of CMI might be in the range 2-3, which is consistent with recent findings about the development of herpes zoster. We also show that the estimate of the age at which the last re-exposure to VZV occurs is highly sensitive to the underlying form of age dependence of the force of infection.; CONCLUSIONS: Our results contribute to the study of the potential immunity boosting effect of re-exposures to an infective agent by quantifying the re-exposure process. Copyright 2013 Elsevier Inc. All rights reserved
Influenza in workplaces: Transmission, workers' adherence to sick leave advice and European sick leave recommendations
No full textKnowledge about influenza transmission in the workplace and whether staying home from work when experiencing influenza-like illness can reduce the spread of influenza is crucial for the design of efficient public health initiatives
- …
