Health metrics for helminthic infections

Over the past five decades, accurate and comparable assessment of disease burden due to different 'worm' infections has proven problematic. Estimates of the health impact of helminths have varied significantly, depending on the assessor's perspective and the approaches taken to quantifying disease effects on patient performance status. Past surveys have frequently suffered from misclassification bias due to the lack of a diagnostic 'gold' standard. At the same time, there has been a tendency to define disease based solely on late-onset, 'pathognomonic' outcomes that can be uniquely attributed to each pathogen. However, we are now gaining a much better understanding of the role of helminths in anaemia causation, impaired growth and development, and poor school or work performance. With a new appreciation of the link between long-term, parasite-mediated inflammation and the patient's lifetime risk of disability, we recognise that the bulk of worm-associated diseases is found in the latter, 'non-specific' categories, with relevance to individual performance status and detriment to regional levels of human capital. Appropriately, the emerging use of comprehensive disability metrics such as the quality-adjusted life year (QALY)-as opposed to the widely used disability-adjusted life year (DALY) metrics-will better capture the impact of helminthic infections on the long-term health of Asian and other developing world populations. This improved, more valid assessment is expected to provide evidence favouring preventive over curative intervention for control of these highly prevalent diseases.