Villate José I, Ibáñez Berta, Cabriada Valentín, Pijoán José I, Taboada Jorge, Urkaregi Arantza
Preventive Medicine Department, Cruces Hospital, Barakaldo, Spain.
BMC Public Health. 2006 Sep 28;6:240. doi: 10.1186/1471-2458-6-240.
Estimation of the frequency of latent tuberculosis infection (LTBI) is difficult in areas with low tuberculosis infection rates and high exposure to non-tuberculous mycobacteria (NTM), including BCG vaccination. The objective was to assess LTBI and M avium infection and to estimate their probability based on skin tests responses in an infant population from a region with the aforementioned characteristics.
A population-based tuberculin skin test (TST) and sensitin (M avium) survey was conducted on seven years old infants in Biscay, a province from The Basque Country (Spain). 2268 schoolchildren received sensitin and 5277 TST. Participation rate was 89%. Commonly used estimation methods were compared with a method based on the fit of mixture models using the Expectation Maximization algorithm. Functions estimating the probabilities of LTBI and M avium infection given the observed skin tests responses were developed for vaccinated and unvaccinated children.
LTBI prevalences varied widely according to the estimation method. The mixture model provided prevalences higher than expected although intermediates between those obtained by currently recommended approaches. Exposure to previous BCG vaccine produces an upward shift of an average of about 3 mm on the induration size to attain the same probability of infection.
Our results confirm the commonplace exposure to NTM which effect should be taken into account when performing and assessing tuberculin surveys. The use of mixture analysis under the empirical Bayes framework allows to better estimate the probability of LTBI in settings with presence of other NTM and high BCG-vaccination coverage. An estimation of the average effect of BCG vaccination on TST induration is also provided. These models maximise information coming from classical tuberculin surveys and could be used together with the newly developed blood tests to improve survey's specificity and cost-effectiveness.
在结核病感染率低且非结核分枝杆菌（NTM）暴露率高（包括卡介苗接种）的地区，估计潜伏性结核感染（LTBI）的频率很困难。目的是评估LTBI和鸟分枝杆菌感染，并根据上述特征地区婴儿群体的皮肤试验反应估计其概率。
在西班牙巴斯克地区的比斯开省对7岁婴儿进行了一项基于人群的结核菌素皮肤试验（TST）和敏感菌素（鸟分枝杆菌）调查。2268名学童接受了敏感菌素检测，5277名接受了TST检测。参与率为89%。将常用的估计方法与基于期望最大化算法的混合模型拟合方法进行了比较。针对接种和未接种疫苗的儿童，开发了根据观察到的皮肤试验反应估计LTBI和鸟分枝杆菌感染概率的函数。
根据估计方法的不同，LTBI患病率差异很大。混合模型得出的患病率高于预期，尽管处于当前推荐方法所得结果之间。既往接种卡介苗会使硬结大小平均上移约3毫米，以达到相同的感染概率。
我们的结果证实了NTM的普遍暴露，在进行和评估结核菌素调查时应考虑其影响。在经验贝叶斯框架下使用混合分析可以更好地估计在存在其他NTM且卡介苗接种覆盖率高的情况下LTBI的概率。还提供了卡介苗接种对TST硬结的平均影响估计。这些模型最大限度地利用了经典结核菌素调查的信息，可与新开发的血液检测一起使用，以提高调查的特异性和成本效益。
