title: Sensitivity and specificity of pooled faecal culture and serology as flock-screening tests for detection of ovine paratuberculosis in Australia.
abstract: The flock-level sensitivity of pooled faecal culture and serological testing using AGID for the detection of ovine Johne's disease-infected flocks were estimated using non-gold-standard methods. The two tests were compared in an extensive field trial in 296 flocks in New South Wales during 1998. In each flock, a sample of sheep was selected and tested for ovine Johne's disease using both the AGID and pooled faecal culture. The flock-specificity of pooled faecal culture also was estimated from results of surveillance and market-assurance testing in New South Wales. The overall flock-sensitivity of pooled faecal culture was 92% (95% CI: 82.4 and 97.4%) compared to 61% (50.5 and 70.9%) for serology (assuming that both tests were 100% specific). In low-prevalence flocks (estimated prevalence <2%), the flock-sensitivities of pooled faecal culture and serology were 82% (57 and 96%) and 33% (19 and 49%), respectively, compared to 96% (85 and 99.5%) and 85% (72 and 93%), respectively, in higher-prevalence flocks (estimated prevalence > or =2%). A Bayesian approach incorporating prior knowledge on flock-specificity of pooled culture produced similar estimates and probability intervals. These estimates assume conditional independence of the two tests, and therefore might have over-estimated the true flock-sensitivities of the tests if the flock-sensitivities of pooled faecal culture and serology were correlated. The estimated minimum flock-specificity of pooled culture when used for surveillance and assurance testing was 99.1% (96.9 and 99.9%). Surveillance and assurance programs in Australia are designed to provide a flock-sensitivity of 95% for an assumed prevalence of 2%. Pooled faecal culture is performing at close to this level--whereas the flock-sensitivity of serology appears to be lower than expected, particularly in lower prevalence flocks.
authors.affiliation: NSW Agriculture, Locked Bag 21, 2800, NSW, Orange, Australia. evan@ausvet.com.au
authors.forename: E S G
authors.initials: ES
authors.lastname: Sergeant
authors.forename: R J
authors.initials: RJ
authors.lastname: Whittington
authors.forename: S J
authors.initials: SJ
authors.lastname: More
mesh_terms: D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood; D001499:Bayes Theorem; D015169:Colony Count, Microbial; D005243:Feces / Q000382:microbiology; D008403:Mass Screening / Q000379:methods / Q000662:veterinary*; D016927:Mycobacterium avium subsp. paratuberculosis / Q000276:immunology / Q000302:isolation & purification; D009517:New South Wales / Q000453:epidemiology; D010283:Paratuberculosis / Q000097:blood / Q000175:diagnosis* / Q000453:epidemiology*; D015995:Prevalence; D012680:Sensitivity and Specificity; D012756:Sheep; D012757:Sheep Diseases / Q000097:blood / Q000175:diagnosis* / Q000453:epidemiology*
chemical_list: D000907:Antibodies, Bacterial