There has been a tremendous increase in recent years of population-based diagnostic monitoring and surveillance strategies in swine populations. One example is the use of processing fluids (PF) to screen breeding herds for porcine reproductive and respiratory syndrome virus (PRRSV) activity. An important question from practitioners using such methods is on how intensively can the sample be pooled. More specifically, processing fluids of how many litters can be pooled into a single sample for diagnostic testing to preserve a high probability of PRRSV RNA detection at low prevalence situations? The objective of this study was to model the effect of pooling PF samples on the probability of PRRSV RNA detection. For this study, a PRRSV-positive PF field sample with a RT-rtPCR quantification cycle (Cq) value of 28 was selected to represent a litter of 11 pigs with a single viremic piglet. PF samples from a PRRSV-naïve herd were used to perform 6 replications of 8 two-fold serial dilutions of the PRRSV-positive sample, thus modeling the pooling effect (dilution). Each two-fold dilution represented an increase in the number of PRRS-negative pigs in the sample by a factor of 2. Samples were tested for PRRSV RNA by RT-rtPCR and the data was analyzed using linear and probit regression models. There was an average increment of 1.37 points in Ct for each two-fold dilution. The estimated probability of testing positive on RT-rtPCR was 43 %, 80 %, and 95 % when there was a single PRRSv-positive piglet among 784, 492, and 323 PRRSv-negative piglets contributing to the sample respectively. Results from this study support the practice of collecting and aggregating PF samples from multiple litters for PRRSV RNA testing.

近年来，基于人群的诊断监测和监测策略在猪群中大幅增加。一个例子是使用加工液 (PF) 来筛选种猪群的猪繁殖与呼吸综合征病毒 (PRRSV) 活动。使用此类方法的从业者提出的一个重要问题是，样本的集中程度如何。更具体地说，可以将多少窝处理液汇集到一个样本中进行诊断测试，以在低流行情况下保持高概率的 PRRSV RNA 检测？本研究的目的是模拟合并 PF 样本对 PRRSV RNA 检测概率的影响。对于这项研究，选择 RT-rtPCR 定量循环 (Cq) 值为 28 的 PRRSV 阳性 PF 现场样品来代表一窝有单个病毒血症仔猪的 11 头猪。来自 PRRSV 未感染群体的 PF 样本被用于对 PRRSV 阳性样本进行 8 次两倍系列稀释的 6 次重复，从而模拟汇集效应（稀释）。每两倍稀释代表样品中 PRRS 阴性猪的数量增加 2 倍。通过 RT-rtPCR 测试样品的 PRRSV RNA，并使用线性和概率回归模型分析数据。每稀释两倍，Ct 平均增加 1.37 个点。当 784、492、784 只 PRRSv 阳性仔猪中存在一头 PRRSv 阳性仔猪时，RT-rtPCR 检测呈阳性的估计概率为 43%、80% 和 95%。和 323 头 PRRSv 阴性仔猪分别对样本有贡献。这项研究的结果支持从多窝收集和聚合 PF 样本以进行 PRRSV RNA 检测的做法。