Centre for Veterinary Epidemiological Research, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, Prince Edward Island, Canada C1A 4P3.
J Dairy Sci. 2011 Jan;94(1):250-61. doi: 10.3168/jds.2010-3559.
Criteria for diagnosing intramammary infections (IMI) have been debated for many years. Factors that may be considered in making a diagnosis include the organism of interest being found on culture, the number of colonies isolated, whether or not the organism was recovered in pure or mixed culture, and whether or not concurrent evidence of inflammation existed (often measured by somatic cell count). However, research using these criteria has been hampered by the lack of a "gold standard" test (i.e., a perfect test against which the criteria can be evaluated) and the need for very large data sets of culture results to have sufficient numbers of quarters with infections with a variety of organisms. This manuscript used 2 large data sets of culture results to evaluate several definitions (sets of criteria) for classifying a quarter as having, or not having an IMI by comparing the results from a single culture to a gold standard diagnosis based on a set of 3 milk samples. The first consisted of 38,376 milk samples from which 25,886 triplicate sets of milk samples taken 1 wk apart were extracted. The second consisted of 784 quarters that were classified as infected or not based on a set of 3 milk samples collected at 2-d intervals. From these quarters, a total of 3,136 additional samples were evaluated. A total of 12 definitions (named A to L) based on combinations of the number of colonies isolated, whether or not the organism was recovered in pure or mixed culture, and the somatic cell count were evaluated for each organism (or group of organisms) with sufficient data. The sensitivity (ability of a definition to detect IMI) and the specificity (Sp; ability of a definition to correctly classify noninfected quarters) were both computed. For all species, except Staphylococcus aureus, the sensitivity of all definitions was <90% (and in many cases<50%). Consequently, if identifying as many existing infections as possible is important, then the criteria for considering a quarter positive should be a single colony (from a 0.01-mL milk sample) isolated (definition A). With the exception of "any organism" and coagulase-negative staphylococci, all Sp estimates were over 94% in the daily data and over 97% in the weekly data, suggesting that for most species, definition A may be acceptable. For coagulase-negative staphylococci, definitions B (2 colonies from a 0.01-mL milk sample) raised the Sp to 92 and 95% in the daily and weekly data, respectively. For "any organism," using definition B raised the Sp to 88 and 93% in the 2 data sets, respectively. The final choice of definition will depend on the objectives of study or control program for which the sample was collected.
用于诊断乳房内感染（IMI）的标准已经争论了很多年。在做出诊断时，可能需要考虑以下因素：感兴趣的生物体在培养物中被发现，分离的菌落数量，生物体是否在纯培养或混合培养中被回收，以及是否存在并发炎症证据（通常通过体细胞计数来衡量）。然而，使用这些标准的研究受到缺乏“金标准”测试（即，可用于评估标准的完美测试）以及需要大量培养结果数据集以获得具有各种生物体的感染的足够数量的 quarters 的阻碍。本文使用了两个大型的培养结果数据集，通过将单个培养物的结果与基于三组牛奶样本的金标准诊断进行比较，评估了几种定义（标准集）用于将 quarters 分类为具有或不具有 IMI 的方法。第一个数据集由 38376 个牛奶样本组成，其中提取了 25886 个相隔 1 周的三重牛奶样本。第二个数据集由 784 个 quarters 组成，这些 quarters 根据每隔两天收集的三组牛奶样本的集合进行感染或不感染的分类。从这些 quarters 中，总共评估了 3136 个其他样本。总共评估了 12 种基于分离的菌落数量、生物体是否在纯培养或混合培养中回收以及体细胞计数的组合的定义（命名为 A 至 L），用于具有足够数据的每种生物体（或生物体组）。对于所有物种，除了金黄色葡萄球菌之外，所有定义的敏感性（定义检测 IMI 的能力）和特异性（Sp；定义正确分类未感染 quarters 的能力）都被计算出来。对于除金黄色葡萄球菌以外的所有物种，所有定义的敏感性均<90%（在许多情况下<50%）。因此，如果确定尽可能多的现有感染非常重要，那么考虑 quarters 阳性的标准应该是从 0.01 毫升牛奶样本中分离出的单个菌落（定义 A）。除了“任何生物体”和凝固酶阴性葡萄球菌外，每日数据中的所有 Sp 估计值均超过 94%，每周数据中的 Sp 估计值均超过 97%，这表明对于大多数物种，定义 A 可能是可以接受的。对于凝固酶阴性葡萄球菌，定义 B（从 0.01 毫升牛奶样本中分离出的 2 个菌落）将 Sp 分别提高到每日和每周数据中的 92%和 95%。对于“任何生物体”，使用定义 B 将 Sp 分别提高到两个数据集的 88%和 93%。定义的最终选择将取决于收集样本的研究或控制计划的目标。
