ArticlesReassessment of the cost of chronic helmintic infection: a meta-analysis of disability-related outcomes in endemic schistosomiasis
Introduction
Chronic schistosomiasis, caused by parasitic blood flukes Schistosoma haematobium, S mansoni, S intercalatum, S mekongi, or S japonicum, is one of the most prevalent infectious diseases. More than 200 million people are infected worldwide, most of whom live in sub-Saharan Africa.1 A mature, patent, schistosome infection is associated with chronic tissue inflammation. The range and potential severity of symptoms and pathological changes associated with schistosomiasis have been well described.2, 3, 4, 5 By contrast, the disabling effects of these clinical manifestations have not been adequately quantified. In particular, population-based studies have not provided a clear estimate of the effect of chronic schistosomiasis on performance status or overall quality-of-life.
In the past two decades, national and international programmes have come to depend on cost-effectiveness analysis for their allocation of health-care resources. This approach needs fairly precise estimates of the disutility (eg, death and disability) of the health conditions that are to be prioritised, and controversy persists over what is the best means to measure and compare the burden of different diseases.6 In 1995–96, as a first approach to effecting this comparison, the Global Burden of Disease Programme developed disability-adjusted life-year (DALY) estimates for many diseases.7 Since then, WHO, the World Bank, and other agencies have used DALY estimates to rank the effect of different diseases on world health. DALY estimates were based on a weighting scale developed by a panel of experts convened in Geneva.7 However, studies have cast doubt on the ability of experts to assess outlook for patients with chronic diseases, characterised by low mortality,8, 9, 10 especially for patients with comorbidities.11, 12 For example, the age-specific DALY weights for schistosomiasis, assigned by the Global Burden of Disease Programme, ranged from 0·005 to 0·006, which is similar to those for disorders such as moderate discolouration of the face (facial vitiligo).13 Although this process was reproducible in terms of the experts' ordinal ranking of disability caused by different disorders, the magnitude of the weights for schistosomiasis and other helmintic infections, as derived by this Delphi method,6, 9 seemed exceptionally low to many specialists.1
Over the past 80 years, several workers in observational and interventional studies have independently attempted to estimate the effect of schistosome infection on the health and performance status of infected individuals. Others have quantified the schistosomiasis-specific risk of morbidities known to be linked to disability. These studies have yielded conflicting conclusions about the functional significance of schistosome infection.14, 15, 16 Our aim was to critically review the available evidence on disability caused by chronic schistosomiasis, and to use summary data from the abstracted studies to develop a working, evidence-based estimate of the disability-weight associated with chronic schistosome infection.
Section snippets
Search strategy
We identified published studies using the National Library of Medicine's MEDLINE computer database and Elsevier's EMBASE database with the key words listed in the (panel). Database searches were restricted to the period from when the earliest electronic records were available (Jan 1, 1966) to when we obtained data for this study (July 31, 2002). Additional studies published before and during this period were identified from the reference lists in the reports, by hand searches of published
Results
Of the 482 reports identified in the initial searches, 135 met the inclusion criteria for our meta-analysis (figure 1). Eligible studies consisted of 133 that were published and two that were unpublished, which were undertaken between 1938 and 2002 (median=1985). 42 were population based, and 92 provided data only for subpopulations (ie, 40 studies of school-age children only; and 52 based on subpopulations selected according to sex, ethnic origin, adult age, employment, clinical status,
Discussion
Our results show a significant association between human schistosome infection and the symptoms of diarrhoea, pain, and fatigue, as well as the objective findings of haemoglobin deficit, undernutrition, and reduced exercise tolerance. Assessment of results, which were consistent across many observational and interventional studies, suggests that there is a significant, infection-associated loss of performance in a person with schistosomiasis, which can be improved, at least in part, through
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