St. Georges University, Department of Public Health and Preventive Medicine, School of Medicine, P.O. Box 7, True Blue, St. Georges, Grenada, West Indies.
Prev Vet Med. 2010 May 1;94(3-4):202-12. doi: 10.1016/j.prevetmed.2010.01.005. Epub 2010 Mar 5.
Monte Carlo simulation was used to determine optimal fecal pool sizes for identification of all Mycobacterium avium subsp. paratuberculosis (MAP)-infected cows in a dairy herd. Two pooling protocols were compared: a halving protocol involving a single retest of negative pools followed by halving of positive pools and a simple protocol involving single retest of negative pools but no halving of positive pools. For both protocols, all component samples in positive pools were then tested individually. In the simulations, the distributions of number of tests required to classify all individuals in an infected herd were generated for various combinations of prevalence (0.01, 0.05 and 0.1), herd size (300, 1000 and 3000), pool size (5, 10, 20 and 50) and test sensitivity (0.5-0.9). Test specificity was fixed at 1.0 because fecal culture for MAP yields no or rare false-positive results. Optimal performance was determined primarily on the basis of a comparison of the distributions of numbers of tests needed to detect MAP-infected cows using the Mann-Whitney U test statistic. Optimal pool size was independent of both herd size and test characteristics, regardless of protocol. When sensitivity was the same for each pool size, pool sizes of 20 and 10 performed best for both protocols for prevalences of 0.01 and 0.1, respectively, while for prevalences of 0.05, pool sizes of 10 and 20 were optimal for the simple and halving protocols, respectively. When sensitivity decreased with increasing pool size, the results changed for prevalences of 0.05 and 0.1 with pool sizes of 50 being optimal especially at a prevalence of 0.1. Overall, the halving protocol was more cost effective than the simple protocol especially at higher prevalences. For detection of MAP using fecal culture, we recommend use of the halving protocol and pool sizes of 10 or 20 when the prevalence is suspected to range from 0.01 to 0.1 and there is no expected loss of sensitivity with increasing pool size. If loss in sensitivity is expected and the prevalence is thought to be between 0.05 and 0.1, the halving protocol and a pool size of 50 is recommended. Our findings are broadly applicable to other infectious diseases under comparable testing conditions.
采用蒙特卡罗模拟方法确定了用于鉴定奶牛场中所有感染分枝杆菌副结核亚种（MAP）奶牛的粪便池最佳大小。比较了两种混合方案：一种是减半方案，包括对阴性池进行单次复测，然后对阳性池减半；另一种是简单方案，只对阴性池进行单次复测，阳性池不减半。对于两种方案，阳性池中的所有混合样本随后都单独进行检测。在模拟中，为各种流行率（0.01、0.05 和 0.1）、畜群大小（300、1000 和 3000）、池大小（5、10、20 和 50）和检测灵敏度（0.5-0.9）组合生成了分类感染畜群中所有个体所需的测试次数分布。由于 MAP 的粪便培养不会产生或很少产生假阳性结果，因此检测特异性固定为 1.0。最优性能主要基于 Mann-Whitney U 检验统计量来比较使用不同方案检测 MAP 感染牛所需的测试次数分布来确定。无论协议如何，最佳池大小都与畜群大小和测试特征无关。当每个池的灵敏度相同时，对于两种方案，当流行率分别为 0.01 和 0.1 时，池大小为 20 和 10 的性能最佳，而当流行率为 0.05 时，简单方案和减半方案的最佳池大小分别为 10 和 20。当灵敏度随池大小增加而降低时，对于流行率为 0.05 和 0.1，池大小为 50 的结果发生变化，尤其是流行率为 0.1 时。总体而言，减半方案比简单方案更具成本效益，尤其是在较高流行率时。对于使用粪便培养检测 MAP，我们建议在流行率疑似为 0.01 至 0.1 之间且池大小增加不会导致灵敏度损失时，使用减半方案和 10 或 20 的池大小。如果预计会出现灵敏度损失，并且认为流行率在 0.05 至 0.1 之间，则建议使用减半方案和 50 的池大小。我们的发现广泛适用于其他在类似检测条件下的传染病。
