COMPARISON OF MICROBIOLOGIC CULTURE, AN ENZYME-LINKED-IMMUNOSORBENT-ASSAY, AND DETERMINATION OF SOMATIC-CELL COUNT FOR DIAGNOSING STAPHYLOCOCCUS-AUREUS MASTITIS IN DAIRY-COWS

Results of using microbiologic culture of a single milk sample, determ ination of somatic cell count (SCC), an ELISA, and a combination of de termination of SCC and ELISA to diagnose Staphylococcus aureus mastiti s in dairy cattle were compared. Cows were considered to have S aureus intramammary infections if microbiologic culture of at least 2 of 3 c onsecutive sets of milk samples yielded growth of the organism. Data w ere analyzed from milk samples collected over a 4-month period from 18 5 cows in 5 herds. Sensitivity, specificity, and likelihood ratio of a positive test result for microbiologic culture of a single milk sampl e weve 93%, 99%, and 93.0, respectively. Sensitivity, specificity, and likelihood ratio of a positive test result for ELISA were 69%, 61%, a nd 1.8, respectively, and for determination of sec, they weve 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 mi crobiologic culture of a single milk sample is the best of the 3 tests studied for diagnosing S aureus intramammary infection.