Bayesian estimation of test characteristics of real-time PCR, bacteriological culture and California mastitis test for diagnosis of intramammary infections with Staphylococcus aureus in dairy cattle at routine milk recordings

Yasser S. Mahmmod; Nils Toft; Jørgen Katholm; Carsten Grønbæk; Ilka C. Klaas

doi:10.1016/j.prevetmed.2013.07.021

Bayesian estimation of test characteristics of real-time PCR, bacteriological culture and California mastitis test for diagnosis of intramammary infections with Staphylococcus aureus in dairy cattle at routine milk recordings

Yasser S. Mahmmod, Nils Toft, Jørgen Katholm, Carsten Grønbæk, Ilka C. Klaas

Research output: Contribution to journal › Article › peer-review

35 Scopus citations

Abstract

Danish farmers can order a real-time PCR mastitis diagnostic test on routinely taken cow-level samples from milk recordings. Validation of its performance in comparison to conventional mastitis diagnostics under field conditions is essential for efficient control of intramammary infections (IMI) with Staphylococcus aureus (S. aureus). Therefore, the objective of this study was to estimate the sensitivity (Se) and specificity (Sp) of real-time PCR, bacterial culture (BC) and California mastitis test (CMT) for the diagnosis of the naturally occurring IMI with S. aureus in routinely collected milk samples using latent class analysis (LCA) to avoid the assumption of a perfect reference test. Using systematic random sampling, a total of 609 lactating dairy cows were selected from 6 dairy herds with bulk tank milk PCR cycle threshold (Ct) value ≤39 for S. aureus. At routine milk recordings, automatically obtained cow-level (composite) milk samples were analyzed by PCR and at the same milking, 2436 quarter milk samples were collected aseptically for BC and CMT. Results showed that 140 cows (23%) were positive for S. aureus IMI by BC while 170 cows (28%) were positive by PCR. Estimates of Se and Sp for PCR were higher than test estimates of BC and CMT. Se_CMT was higher than Se_BC however, Sp_BC was higher than Sp_CMT. Se_PCR was 91%, while Se_BC was 53%, and Se_CMT was 61%. Sp_PCR was 99%, while Sp_BC was 89%, and Sp_CMT was 65%.In conclusion, PCR has a higher performance than the conventional diagnostic tests (BC and CMT) suggesting its usefulness as a routine test for accurate diagnosis of S. aureus IMI from dairy cows at routine milk recordings. The use of LCA provided estimates of the test characteristics for two currently diagnostic tests (BC, CMT) and a novel technique (real-time PCR) for diagnosing S. aureus IMI under field conditions at routine milk recordings in Denmark.

Original language	English (US)
Pages (from-to)	309-317
Number of pages	9
Journal	Preventive Veterinary Medicine
Volume	112
Issue number	3-4
DOIs	https://doi.org/10.1016/j.prevetmed.2013.07.021
State	Published - Nov 1 2013
Externally published	Yes

Bibliographical note

Funding Information:
This research work was funded by Faculty of Health and Medical Sciences, University of Copenhagen . The authors gratefully wish to acknowledge staff of Eurofins Steins Laboratory for providing us the lab space to conduct this research and for their technical and logistic support. They would like to thank Knowledge Centre for Agriculture, Cattle for funding of PCR testing and also, the technicians for their support in samples collection. Thanks to the Danish farmers for their help and making their cows available for our study.

Keywords

Conventional diagnostics
Dairy cows
PathoProof™ Mastitis PCR assay
Sensitivity and Specificity
Staphylococcus aureus
Test misclassification

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10.1016/j.prevetmed.2013.07.021

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Mahmmod, Y. S., Toft, N., Katholm, J., Grønbæk, C., & Klaas, I. C. (2013). Bayesian estimation of test characteristics of real-time PCR, bacteriological culture and California mastitis test for diagnosis of intramammary infections with Staphylococcus aureus in dairy cattle at routine milk recordings. Preventive Veterinary Medicine, 112(3-4), 309-317. https://doi.org/10.1016/j.prevetmed.2013.07.021

Bayesian estimation of test characteristics of real-time PCR, bacteriological culture and California mastitis test for diagnosis of intramammary infections with Staphylococcus aureus in dairy cattle at routine milk recordings. / Mahmmod, Yasser S.; Toft, Nils; Katholm, Jørgen et al.
In: Preventive Veterinary Medicine, Vol. 112, No. 3-4, 01.11.2013, p. 309-317.

Research output: Contribution to journal › Article › peer-review

Mahmmod, YS, Toft, N, Katholm, J, Grønbæk, C & Klaas, IC 2013, 'Bayesian estimation of test characteristics of real-time PCR, bacteriological culture and California mastitis test for diagnosis of intramammary infections with Staphylococcus aureus in dairy cattle at routine milk recordings', Preventive Veterinary Medicine, vol. 112, no. 3-4, pp. 309-317. https://doi.org/10.1016/j.prevetmed.2013.07.021

Mahmmod YS, Toft N, Katholm J, Grønbæk C, Klaas IC. Bayesian estimation of test characteristics of real-time PCR, bacteriological culture and California mastitis test for diagnosis of intramammary infections with Staphylococcus aureus in dairy cattle at routine milk recordings. Preventive Veterinary Medicine. 2013 Nov 1;112(3-4):309-317. doi: 10.1016/j.prevetmed.2013.07.021

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abstract = "Danish farmers can order a real-time PCR mastitis diagnostic test on routinely taken cow-level samples from milk recordings. Validation of its performance in comparison to conventional mastitis diagnostics under field conditions is essential for efficient control of intramammary infections (IMI) with Staphylococcus aureus (S. aureus). Therefore, the objective of this study was to estimate the sensitivity (Se) and specificity (Sp) of real-time PCR, bacterial culture (BC) and California mastitis test (CMT) for the diagnosis of the naturally occurring IMI with S. aureus in routinely collected milk samples using latent class analysis (LCA) to avoid the assumption of a perfect reference test. Using systematic random sampling, a total of 609 lactating dairy cows were selected from 6 dairy herds with bulk tank milk PCR cycle threshold (Ct) value ≤39 for S. aureus. At routine milk recordings, automatically obtained cow-level (composite) milk samples were analyzed by PCR and at the same milking, 2436 quarter milk samples were collected aseptically for BC and CMT. Results showed that 140 cows (23%) were positive for S. aureus IMI by BC while 170 cows (28%) were positive by PCR. Estimates of Se and Sp for PCR were higher than test estimates of BC and CMT. SeCMT was higher than SeBC however, SpBC was higher than SpCMT. SePCR was 91%, while SeBC was 53%, and SeCMT was 61%. SpPCR was 99%, while SpBC was 89%, and SpCMT was 65%.In conclusion, PCR has a higher performance than the conventional diagnostic tests (BC and CMT) suggesting its usefulness as a routine test for accurate diagnosis of S. aureus IMI from dairy cows at routine milk recordings. The use of LCA provided estimates of the test characteristics for two currently diagnostic tests (BC, CMT) and a novel technique (real-time PCR) for diagnosing S. aureus IMI under field conditions at routine milk recordings in Denmark.",

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AU - Toft, Nils

AU - Katholm, Jørgen

AU - Grønbæk, Carsten

AU - Klaas, Ilka C.

N1 - Funding Information: This research work was funded by Faculty of Health and Medical Sciences, University of Copenhagen . The authors gratefully wish to acknowledge staff of Eurofins Steins Laboratory for providing us the lab space to conduct this research and for their technical and logistic support. They would like to thank Knowledge Centre for Agriculture, Cattle for funding of PCR testing and also, the technicians for their support in samples collection. Thanks to the Danish farmers for their help and making their cows available for our study.

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AB - Danish farmers can order a real-time PCR mastitis diagnostic test on routinely taken cow-level samples from milk recordings. Validation of its performance in comparison to conventional mastitis diagnostics under field conditions is essential for efficient control of intramammary infections (IMI) with Staphylococcus aureus (S. aureus). Therefore, the objective of this study was to estimate the sensitivity (Se) and specificity (Sp) of real-time PCR, bacterial culture (BC) and California mastitis test (CMT) for the diagnosis of the naturally occurring IMI with S. aureus in routinely collected milk samples using latent class analysis (LCA) to avoid the assumption of a perfect reference test. Using systematic random sampling, a total of 609 lactating dairy cows were selected from 6 dairy herds with bulk tank milk PCR cycle threshold (Ct) value ≤39 for S. aureus. At routine milk recordings, automatically obtained cow-level (composite) milk samples were analyzed by PCR and at the same milking, 2436 quarter milk samples were collected aseptically for BC and CMT. Results showed that 140 cows (23%) were positive for S. aureus IMI by BC while 170 cows (28%) were positive by PCR. Estimates of Se and Sp for PCR were higher than test estimates of BC and CMT. SeCMT was higher than SeBC however, SpBC was higher than SpCMT. SePCR was 91%, while SeBC was 53%, and SeCMT was 61%. SpPCR was 99%, while SpBC was 89%, and SpCMT was 65%.In conclusion, PCR has a higher performance than the conventional diagnostic tests (BC and CMT) suggesting its usefulness as a routine test for accurate diagnosis of S. aureus IMI from dairy cows at routine milk recordings. The use of LCA provided estimates of the test characteristics for two currently diagnostic tests (BC, CMT) and a novel technique (real-time PCR) for diagnosing S. aureus IMI under field conditions at routine milk recordings in Denmark.

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Bayesian estimation of test characteristics of real-time PCR, bacteriological culture and California mastitis test for diagnosis of intramammary infections with Staphylococcus aureus in dairy cattle at routine milk recordings

Abstract

Bibliographical note

Keywords

Publisher link

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