Latent class analysis of the diagnostic characteristics of PCR and conventional bacteriological culture in diagnosing intramammary infections caused by Staphylococcus aureus in dairy cows at dry offReport as inadecuate




Latent class analysis of the diagnostic characteristics of PCR and conventional bacteriological culture in diagnosing intramammary infections caused by Staphylococcus aureus in dairy cows at dry off - Download this document for free, or read online. Document in PDF available to download.

Acta Veterinaria Scandinavica

, 54:65

First Online: 20 November 2012Received: 13 June 2012Accepted: 15 November 2012

Abstract

BackgroundStaphylococcus aureus is one of the most common causes of intramammary infections in dairy cows at dry off. Reliable identification is important for disease management on herd level and for antimicrobial treatment of infected animals. Our objective was to evaluate the test characteristics of PathoProof ™ Mastitis PCR Assay and bacteriological culture BC in diagnosing bovine intramammary infections caused by S. aureus at dry off at different PCR cycle threshold Ct-value cut-offs.

MethodsSterile quarter samples and non-sterile composite samples from 140 animals in seven herds were collected in connection with the dairy herd improvement DHI milk recording. All quarter samples were analyzed using BC whereas all composite samples were analyzed with PathoProof ™ Mastitis PCR Assay. Latent class analysis was used to estimate test properties for PCR and BC in the absence of a perfect reference test. The population was divided into two geographically divided subpopulations and the Hui-Walter 2-test 2-populations model applied to estimate Se, Sp for the two tests, and prevalence for the two subpopulations.

ResultsThe Se for PCR increased with increasing Ct-value cut-off, accompanied by a small decrease in Sp. For BC the Se decreased and Sp increased with increasing Ct-value cut-off. Most optimal test estimates for the real-time PCR assay were at a Ct-value cut-off of 37; 0.93 95% posterior probability interval PPI 0.60-0.99 for Se and 0.95 95% PPI 0.95-0.99 for Sp. At the same Ct-value cut-off, Se and Sp for BC were 0.83 95% PPI 0.66-0.99 and 0.97 95% PPI 0.91-0.99 respectively. Depending on the chosen PCR Ct-value cut-off, the prevalence in the subpopulations varied; the prevalence increased with increasing PCR Ct-value cut-offs.

ConclusionNeither BC nor real-time PCR is a perfect test in detecting IMI in dairy cows at dry off. The changes in sensitivity and prevalence at different Ct-value cut-offs for both PCR and BC may indicate a change in the underlying disease definition. At low PCR Ct-value cut-offs the underlying disease definition may be a truly-heavily infected cow, whereas at higher PCR Ct-value cut-offs the disease definition may be a S. aureus positive cow.

KeywordsStaphylococcus aureus PCR Latent class analysis Sensitivity Specificity Mastitis Bacteriological culture  Download fulltext PDF



Author: Sara Ellinor Cederlöf - Nils Toft - Bent Aalbaek - Ilka Christine Klaas

Source: https://link.springer.com/







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