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Latent class analysis of real time qPCR and bacteriological culturing for the diagnosis of Streptococcus agalactiae in cow composite milk samples.
- Source :
-
Preventive veterinary medicine [Prev Vet Med] 2018 Jun 01; Vol. 154, pp. 119-123. Date of Electronic Publication: 2018 Mar 22. - Publication Year :
- 2018
-
Abstract
- Streptococcus agalactiae (S. agalactiae) has re-emerged as a mastitis pathogen among Norwegian dairy cows. The Norwegian cattle health services recommend that infected herds implement measures to eradicate S. agalactiae, this includes a screening of milk samples from all lactating cows. The performance of the qPCR-test currently in use for this purpose has not been evaluated under field conditions. The objective of this study was to estimate the sensitivity and specificity of the real-time qPCR assay in use in Norway (Mastitis 4 qPCR, DNA Diagnostics A/S, Risskov, Denmark) and compare it to conventional bacteriological culturing for detection of S. agalactiae in milk samples. Because none of these tests are considered a perfect reference test, the evaluation was performed using latent class models in a Bayesian analysis. Aseptically collected cow-composite milk samples from 578 cows belonging to 6 herds were cultured and tested by qPCR. While 37 (6.4%) samples were positive for S. agalactiae by bacteriological culture, 66 (11.4%) samples were positive by qPCR. The within-herd prevalence in the six herds, as estimated by the latent class models ranged from 7.7 to 50.8%. At the recommended cut-off (cycle threshold 37), the sensitivity of the qPCR was significantly higher at 95.3 (95% posterior probability interval [PPI] [84.2; 99.6]) than that of bacteriological culture at 58.2 (95% PPI [43.8; 74.4]). However, bacterial culture had a higher specificity of 99.7 (95% PPI [98.5; 100.0]) compared to the qPCR at 98.5 (95% PPI [94.6; 99.9]). The median estimated negative predictive values of qPCR was consistently higher than those of the BC at all estimated prevalences, and the superiority of the qPCR increased with increasing within-herd prevalence. The median positive predictive values of BC was in general higher than the estimates for the qPCR, however, at the highest prevalence the predictive ability of both tests were similar.<br /> (Copyright © 2018 Elsevier B.V. All rights reserved.)
- Subjects :
- Animals
Bayes Theorem
Cattle
DNA, Bacterial chemistry
DNA, Bacterial genetics
Denmark
Female
Lactation
Mastitis, Bovine microbiology
Norway
Sensitivity and Specificity
Streptococcal Infections diagnosis
Streptococcal Infections microbiology
Streptococcus agalactiae genetics
Milk microbiology
Polymerase Chain Reaction veterinary
Streptococcal Infections veterinary
Streptococcus agalactiae isolation & purification
Subjects
Details
- Language :
- English
- ISSN :
- 1873-1716
- Volume :
- 154
- Database :
- MEDLINE
- Journal :
- Preventive veterinary medicine
- Publication Type :
- Academic Journal
- Accession number :
- 29685435
- Full Text :
- https://doi.org/10.1016/j.prevetmed.2018.03.019