Differing Methods and Definitions Influence DALY estimates: Using Population-Based Data to Calculate the Burden of Convulsive Epilepsy in Rural South Africa

BackgroundThe disability adjusted life year (DALY) is a composite measure of disease burden that includes both morbidity and mortality, and is relevant to conditions such as epilepsy that can limit productive functioning. The 2010 Global Burden of Disease (GBD) study introduced a number of new methods and definitions, including a prevalence-based approach and revised disability weights to calculate morbidity and new standard life expectancies to calculate premature mortality. We used these approaches, and local, population-based data, to estimate the burden of convulsive epilepsy in rural South Africa.Methods & FindingsComprehensive prevalence, incidence and mortality data on convulsive epilepsy were collected within the Agincourt sub-district in rural northeastern South Africa between 2008 and 2012. We estimated DALYs using both prevalence- and incidence-based approaches for calculating years of life lived with disability. Additionally, we explored how changing the disease model by varying the disability weights influenced DALY estimates. Using the prevalence-based approach, convulsive epilepsy in Agincourt resulted in 332 DALYs (95% uncertainty interval (UI): 216–455) and 4.1 DALYs per 1,000 individuals (95%UI: 2.7–5.7) annually. Of this, 26% was due to morbidity while 74% was due to premature mortality. DALYs increased by 10% when using the incidence-based method. Varying the disability weight from 0.072 (treated epilepsy, seizure free) to 0.657 (severe epilepsy) caused years lived with disability to increase from 18 (95%UI: 16–19) to 161 (95%UI: 143–170).ConclusionsDALY estimates are influenced by both the methods applied and population parameters used in the calculation. Irrespective of method, a significant burden of epilepsy is due to premature mortality in rural South Africa, with a lower burden than rural Kenya. Researchers and national policymakers should carefully interrogate the methods and data used to calculate DALYs as this will influence policy priorities and resource allocation.**背景** 残疾调整生命年（disability adjusted life year, DALY）是一类综合衡量疾病负担的指标，同时纳入发病与死亡两个维度，适用于癫痫这类可损害个体生产功能的疾病。2010年全球疾病负担（Global Burden of Disease, GBD）研究提出了一系列全新方法与定义，包括基于患病率的测算框架、用于发病损失估算的修订版残疾权重，以及用于早死损失估算的标准化预期寿命新方案。本研究采用该研究的方法体系，并结合当地基于人群的调查数据，对南非农村地区的惊厥性癫痫疾病负担进行了估算。 **方法与结果** 2008至2012年间，研究人员在南非东北部农村地区的阿金库尔分辖区内，收集了惊厥性癫痫的全面患病率、发病率与死亡率数据。本研究分别采用基于患病率与基于发病率的两种测算框架，估算了因残疾损失的生存年数对应的残疾调整生命年。此外，本研究还探讨了通过调整残疾权重以变更疾病模型的方式，对DALY估算结果的影响。 采用基于患病率的测算框架时，阿金库尔地区的惊厥性癫痫每年造成332个DALY损失（95%不确定区间（uncertainty interval, UI）：216~455），即每千人每年损失4.1个DALY（95%UI：2.7~5.7）。其中26%的损失源于发病相关残疾，74%源于早死。采用基于发病率的测算方法时，DALY损失总量上升10%。当残疾权重从0.072（接受治疗且无癫痫发作者）调整至0.657（重症癫痫患者）时，残疾生存年数从18（95%UI：16~19）升至161（95%UI：143~170）。 **结论** 残疾调整生命年的估算结果受所采用的测算方法与计算中使用的人群参数双重影响。无论采用何种测算方法，南非农村地区的癫痫疾病负担均以早死相关损失为主，且其负担水平低于肯尼亚农村地区。研究人员与国家政策制定者应审慎审视DALY测算所采用的方法与数据，因其将直接影响政策优先级设定与资源分配。