Evaluation of 5 serologic assays to detect Rhodococcus equi pneumonia in foals.
OBJECTIVE
To determine the sensitivity and specificity of 5 serologic assays used to diagnose Rhodococcus equi pneumonia in foals and to determine whether any of the assays could be used to identify affected foals prior to the onset of clinical signs or to differentiate between affected and unaffected foals when clinical signs first become apparent.


METHODS
Nested case-control study.


METHODS
26 foals.


METHODS
Serum samples were obtained from all foals at 2, 4, and 6 or 7 weeks of age. Additional samples were obtained from affected foals at the time of diagnosis of R equi pneumonia and from age-matched unaffected foals. Samples were tested with 3 ELISA, an agar gel immunodiffusion assay, and a synergistic hemolysis inhibition assay.


RESULTS
Sensitivity and specificity data indicated that none of the assays could be used to reliably differentiate affected from unaffected foals at any testing period. Proportions of foals that had an increase in test values between paired samples collected at 4 and 6 or 7 weeks of age were not significantly different between affected and unaffected foals. For all assays, result values increased significantly over time; however, the rate of increase was not significantly different between affected and unaffected foals.


CONCLUSIONS
Results suggest that serologic assays, whether performed on single or paired samples, cannot be used to reliably establish, confirm, or exclude a diagnosis of R equi pneumonia in foals.
D000193:Actinomycetales Infections / Q000175:diagnosis / Q000276:immunology / Q000662:veterinary*; D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood*; D016022:Case-Control Studies; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods / Q000662:veterinary; D006462:Hemolytic Plaque Technique / Q000662:veterinary; D006734:Horse Diseases / Q000097:blood / Q000175:diagnosis* / Q000276:immunology; D006736:Horses; D005779:Immunodiffusion / Q000379:methods / Q000662:veterinary; D018410:Pneumonia, Bacterial / Q000175:diagnosis / Q000276:immunology / Q000662:veterinary*; D016929:Rhodococcus equi / Q000276:immunology* / Q000302:isolation & purification; D012680:Sensitivity and Specificity
D000907:Antibodies, Bacterial