Quantitative Veterinary Epidemiology Group, Wageningen Institute of Animal Sciences, Wageningen University, PO Box 338, 6700 AH Wageningen, The Netherlands.
Vet Microbiol. 2011 Jan 27;147(3-4):440-4. doi: 10.1016/j.vetmic.2010.07.021. Epub 2010 Jul 30.
Since the first report on methicillin resistant Staphylococcus aureus (MRSA) CC398 in pigs, several countries have determined the prevalence of MRSA-positive pig herds using different sampling and laboratory techniques. The objective of the study was to compare three sampling methods for MRSA-classification of herds. Therefore, nasal swabs of pigs and environmental wipes were collected from 147 herds with breeding pigs. Per herd, laboratory examination was done on 10 pools of 6 nasal swabs (NASAL), 5 single environmental wipes (ENVSINGLE) and one pool of 5 environmental wipes (ENVPOOL). Large differences in apparent prevalence of MRSA-positive herds between methods were found: 19.1% for ENVPOOL, 53.1% for ENVSINGLE, and 70.8% for NASAL. Pairwise comparisons of methods resulted in relative sensitivities of 26.9% (ENVPOOL vs. NASAL), 34.6% (ENVPOOL vs. ENVSINGLE), and 72.1% (ENVSINGLE vs. NASAL) with relative specificities of respectively 100%, 98.6% and 93.0%. Cohen's kappa was respectively 0.18, 0.32 and 0.55, thus varying between very poor and moderate agreement. Examination of environmental wipes is an easy and non-invasive method to classify herds for MRSA. The number of environmental wipes needed depends on e.g. required detection limits and within-herd prevalence. In low prevalent herds (e.g. herds with <3 positive pools of nasal swabs), 25 single environmental wipes are required to be 90% sure that MRSA is detected at a detection limit similar to analyzing 10 pools of nasal swabs. Individual analysis of environmental wipes is highly recommended, as pooling 5 environmental samples resulted in a substantial reduction of the apparent prevalence.
自首次报道耐甲氧西林金黄色葡萄球菌（MRSA）CC398 存在于猪中以来，许多国家已经使用不同的采样和实验室技术确定了 MRSA 阳性猪群的流行率。本研究的目的是比较三种采样方法对猪群 MRSA 分类的效果。因此，从 147 个有繁殖猪的猪群中采集了猪的鼻腔拭子和环境拭子。每个猪群均对 10 个鼻腔拭子（NASAL）、5 个单个环境拭子（ENVSINGLE）和 1 个环境拭子（ENVPOOL）的 5 个混合样本进行了实验室检查。发现三种方法检测到的 MRSA 阳性猪群的明显流行率存在很大差异：ENVPOOL 为 19.1%，ENVSINGLE 为 53.1%，NASAL 为 70.8%。方法之间的两两比较结果显示，相对敏感性分别为 26.9%（ENVPOOL 与 NASAL）、34.6%（ENVPOOL 与 ENVSINGLE）和 72.1%（ENVSINGLE 与 NASAL），相对特异性分别为 100%、98.6%和 93.0%。Cohen's kappa 值分别为 0.18、0.32 和 0.55，表明一致性在极差和中度之间变化。检查环境拭子是一种简单且非侵入性的方法，可用于对 MRSA 进行猪群分类。所需的环境拭子数量取决于例如所需的检测限和群内流行率。在低流行率的猪群中（例如，鼻腔拭子中有<3 个阳性混合样本的猪群），需要采集 25 个单独的环境拭子，才能在类似分析 10 个鼻腔拭子混合样本的检测限下 90%确定检测到 MRSA。强烈建议对环境拭子进行单独分析，因为混合 5 个环境样本会大大降低明显的流行率。
