Comparison of microbiologic culture, an enzyme-linked immunosorbent assay, and determination of somatic cell count for diagnosing Staphylococcus aureus mastitis in dairy cows

Cathleen R. Hicks From the Department of Veterinary Science, College of Agricultural Sciences, The Pennsylvania State University, University Park, PA 16802.

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Robert J. Eberhart From the Department of Veterinary Science, College of Agricultural Sciences, The Pennsylvania State University, University Park, PA 16802.

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 VMD, PhD
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William M. Sischo From the Department of Veterinary Science, College of Agricultural Sciences, The Pennsylvania State University, University Park, PA 16802.

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Summary

Results of using microbiologic culture of a single milk sample, determination of somatic cell count (scc), an elisa, and a combination of determination of scc and elisa to diagnose Staphylococcus aureus mastitis in dairy cattle were compared. Cows were considered to have S aureus intramammary infections if microbiologic culture of at least 2 of 3 consecutive sets of milk samples yielded growth of the organism. Data were analyzed from milk samples collected over a 4-month period from 185 cows in 5 herds. Sensitivity, specificity, and likelihood ratio of a positive test result for microbiologic culture of a single milk sample were 93%, 99%, and 93.0, respectively. Sensitivity, specificity, and likelihood ratio of a positive test result for elisa were 69%, 61%, and 1.8, respectively, and for determination of scc, they were 79%, 72%, and 2.9, respectively. Combination of determination of scc and elisa had sensitivity, specificity, and likelihood ratio of a positive test result of 80%, 62%, and 3.4, respectively. Results from microbiologic culture of consecutive milk samples were more consistent than results of elisa performed on consecutive samples. These data suggest that microbiologic culture of a single milk sample is the best of the 3 tests studied for diagnosing S aureus intramammary infection.

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