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Quantifying the value of a diagnostic test for early detection surveillance

Alexander Mastin: University of Salford

<div>Advances in molecular diagnostics has resulted in the development of rapid diagnostic tests which can be applied in the field with minimal advance training and can give a result in a short period of time. These “in-field diagnostics” (IFDs) can offer a more sensitive method of pathogen detection during the presymptomatic stage of infection, and have been considered valuable for early detection surveillance. However, the costs of development and application of these tests will be greater than those of visual inspection alone, which may affect the sustainability of an early detection surveillance strategy based upon IFD use. In order to identify whether IFDs are a cost effective alternative to visual inspection (for detection at any specified mean incidence), we have developed a simple heuristic which can be used to compare the total cost of early detection surveillance when using either IFDs or visual inspection. Our method explicitly accounts for the “diagnostic lag” period and the diagnostic sensitivity of the test as well as the rate of pathogen spread in the pathosystem in question. We have applied this heuristic to the case of <i>Phytophthora ramorum</i> in the UK. As well as evaluating the performance of two commercially available IFDs for early detection surveillance, we have investigated the optimal surveillance strategy when the performance of the two detection methods is varied - allowing identification of situations where visual inspection may be optimal.</div>

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