Rotolo Marisa L, Sun Yaxuan, Wang Chong, Giménez-Lirola Luis, Baum David H, Gauger Phillip C, Harmon Karen M, Hoogland Marlin, Main Rodger, Zimmerman Jeffrey J
Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA, USA.
Department of Statistics, College of Liberal Arts and Sciences, Iowa State University, Ames, IA, USA.
Vet Microbiol. 2017 Sep;209:20-29. doi: 10.1016/j.vetmic.2017.02.004. Epub 2017 Feb 17.
Formulas and software for calculating sample size for surveys based on individual animal samples are readily available. However, sample size formulas are not available for oral fluids and other aggregate samples that are increasingly used in production settings. Therefore, the objective of this study was to develop sampling guidelines for oral fluid-based porcine reproductive and respiratory syndrome virus (PRRSV) surveys in commercial swine farms. Oral fluid samples were collected in 9 weekly samplings from all pens in 3 barns on one production site beginning shortly after placement of weaned pigs. Samples (n=972) were tested by real-time reverse-transcription PCR (RT-rtPCR) and the binary results analyzed using a piecewise exponential survival model for interval-censored, time-to-event data with misclassification. Thereafter, simulation studies were used to study the barn-level probability of PRRSV detection as a function of sample size, sample allocation (simple random sampling vs fixed spatial sampling), assay diagnostic sensitivity and specificity, and pen-level prevalence. These studies provided estimates of the probability of detection by sample size and within-barn prevalence. Detection using fixed spatial sampling was as good as, or better than, simple random sampling. Sampling multiple barns on a site increased the probability of detection with the number of barns sampled. These results are relevant to PRRSV control or elimination projects at the herd, regional, or national levels, but the results are also broadly applicable to contagious pathogens of swine for which oral fluid tests of equivalent performance are available.
基于个体动物样本计算调查样本量的公式和软件很容易获得。然而，对于生产环境中越来越常用的口腔液体和其他总体样本，样本量公式并不存在。因此，本研究的目的是为商业猪场基于口腔液体的猪繁殖与呼吸综合征病毒（PRRSV）调查制定采样指南。从一个生产场地的3个猪舍的所有猪栏中，在断奶仔猪入栏后不久开始，每周进行9次采样收集口腔液体样本。对样本（n = 972）进行实时逆转录PCR（RT-rtPCR）检测，并使用分段指数生存模型对具有错误分类的区间删失事件发生时间数据的二元结果进行分析。此后，通过模拟研究来研究PRRSV检测的猪栏水平概率与样本量、样本分配（简单随机抽样与固定空间抽样）、检测诊断敏感性和特异性以及猪栏水平患病率之间的函数关系。这些研究提供了按样本量和猪栏内患病率计算的检测概率估计值。使用固定空间抽样进行检测与简单随机抽样一样好，甚至更好。在一个场地对多个猪栏进行采样会随着采样猪栏数量的增加而提高检测概率。这些结果与畜群、区域或国家层面的PRRSV控制或根除项目相关，但这些结果也广泛适用于有等效性能口腔液体检测方法的猪传染性病原体。
