Research Article: Decision-Model Estimation of the Age-Specific Disability Weight for Schistosomiasis Japonica: A Systematic Review of the Literature

Date Published: March 5, 2008

Publisher: Public Library of Science

Author(s): Julia L. Finkelstein, Mark D. Schleinitz, Hélène Carabin, Stephen T. McGarvey, Charles H. King

Abstract: Schistosomiasis is among the most prevalent parasitic infections worldwide. However, current Global Burden of Disease (GBD) disability-adjusted life year estimates indicate that its population-level impact is negligible. Recent studies suggest that GBD methodologies may significantly underestimate the burden of parasitic diseases, including schistosomiasis. Furthermore, strain-specific disability weights have not been established for schistosomiasis, and the magnitude of human disease burden due to Schistosoma japonicum remains controversial. We used a decision model to quantify an alternative disability weight estimate of the burden of human disease due to S. japonicum. We reviewed S. japonicum morbidity data, and constructed decision trees for all infected persons and two age-specific strata, <15 years (y) and ≥15 y. We conducted stochastic and probabilistic sensitivity analyses for each model. Infection with S. japonicum was associated with an average disability weight of 0.132, with age-specific disability weights of 0.098 (<15 y) and 0.186 (≥15 y). Re-estimated disability weights were seven to 46 times greater than current GBD measures; no simulations produced disability weight estimates lower than 0.009. Nutritional morbidities had the greatest contribution to the S. japonicum disability weight in the <15 y model, whereas major organ pathologies were the most critical variables in the older age group. GBD disability weights for schistosomiasis urgently need to be revised, and species-specific disability weights should be established. Even a marginal increase in current estimates would result in a substantial rise in the estimated global burden of schistosomiasis, and have considerable implications for public health prioritization and resource allocation for schistosomiasis research, monitoring, and control.

Partial Text: Schistosomiasis is one of the most prevalent parasitic infections worldwide. An estimated 779 million people are at risk for schistosomiasis, with 207 million infected in 76 countries and territories [1],[2]. Approximately 120 million people are symptomatic and 20 million have severe and debilitating disease [3]–[5]. Schistosomiasis accounts for 1.7 [6],[7] to 4.5 million disability-adjusted life years (DALYs) [8] lost each year worldwide, among the highest of all neglected tropical diseases.

Our findings indicate that age-specific disability weights of 0.098 to 0.186 would be a more appropriate estimate for the burden of human disease due to S. japonicum infection. It is noteworthy that even the most conservative estimates were seven times greater than current GBD disability weights for schistosomiasis (Table 3)[23], [25]–[27].



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