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.
Design—Nested case-control study.
Procedure—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 agematched
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 and Clinical Relevance—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. (J Am Vet Med Assoc 2002;221:825–833)