Institute of Social and Preventive Medicine (ISPM), University of Bern, Switzerland.
PLoS Med. 2011 Jan 18;8(1):e1000390. doi: 10.1371/journal.pmed.1000390.
The World Health Organization estimates that in sub-Saharan Africa about 4 million HIV-infected patients had started antiretroviral therapy (ART) by the end of 2008. Loss of patients to follow-up and care is an important problem for treatment programmes in this region. As mortality is high in these patients compared to patients remaining in care, ART programmes with high rates of loss to follow-up may substantially underestimate mortality of all patients starting ART.
We developed a nomogram to correct mortality estimates for loss to follow-up, based on the fact that mortality of all patients starting ART in a treatment programme is a weighted average of mortality among patients lost to follow-up and patients remaining in care. The nomogram gives a correction factor based on the percentage of patients lost to follow-up at a given point in time, and the estimated ratio of mortality between patients lost and not lost to follow-up. The mortality observed among patients retained in care is then multiplied by the correction factor to obtain an estimate of programme-level mortality that takes all deaths into account. A web calculator directly calculates the corrected, programme-level mortality with 95% confidence intervals (CIs). We applied the method to 11 ART programmes in sub-Saharan Africa. Patients retained in care had a mortality at 1 year of 1.4% to 12.0%; loss to follow-up ranged from 2.8% to 28.7%; and the correction factor from 1.2 to 8.0. The absolute difference between uncorrected and corrected mortality at 1 year ranged from 1.6% to 9.8%, and was above 5% in four programmes. The largest difference in mortality was in a programme with 28.7% of patients lost to follow-up at 1 year.
The amount of bias in mortality estimates can be large in ART programmes with substantial loss to follow-up. Programmes should routinely report mortality among patients retained in care and the proportion of patients lost. A simple nomogram can then be used to estimate mortality among all patients who started ART, for a range of plausible mortality rates among patients lost to follow-up.
世界卫生组织估计，截至 2008 年底，撒哈拉以南非洲地区约有 400 万艾滋病毒感染者开始接受抗逆转录病毒疗法（ART）。在该地区，患者失访和护理不足是治疗项目面临的一个重要问题。由于与留在护理中的患者相比，这些患者的死亡率较高，因此失访率较高的 ART 项目可能会大大低估所有开始接受 ART 的患者的死亡率。
我们开发了一种列线图来校正失访导致的死亡率估计值，这是基于这样一个事实，即治疗计划中所有开始接受 ART 的患者的死亡率是失访患者和留在护理中的患者死亡率的加权平均值。该列线图根据特定时间点失访患者的百分比以及失访和未失访患者死亡率之间的估计比值，给出一个校正因子。然后，将护理中保留的患者的实际死亡率乘以校正因子，以获得考虑所有死亡的计划水平死亡率的估计值。一个网络计算器可直接计算校正后的、具有 95%置信区间（CI）的计划水平死亡率。我们将该方法应用于撒哈拉以南非洲的 11 个 ART 项目。留在护理中的患者在 1 年内的死亡率为 1.4%至 12.0%；失访率为 2.8%至 28.7%；校正因子为 1.2 至 8.0。1 年内未校正和校正后的死亡率之间的绝对差异为 1.6%至 9.8%，四个项目中差异超过 5%。死亡率的最大差异出现在失访率为 1 年的 28.7%的项目中。
在失访率较高的 ART 项目中，死亡率估计值的偏差可能很大。项目应定期报告留在护理中的患者的死亡率以及失访患者的比例。然后，可以使用简单的列线图来估计所有开始接受 ART 的患者的死亡率，以及失访患者的死亡率在一系列合理的范围内。
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