[Comparison of direct smear observations and bacteriologic culture results carried out on equine tracheal secretions].

The aim of the study was to assess the relation between the direct smear observations and bacteriological results carried out on equine tracheal secretions. A total of 304 cases comprising both the direct smear (Gram stain) and the bacteriological culture, over a period of 8 years, were submitted to this retrospective study. Most of the specimens (78%) were obtained using tracheal washings while the rest (22%) originated from tracheal brushings. A total of 96 specimens (32%) were negative for both direct smear and culture. The positive predictive value of direct smears appeared high (81-96%) while the negative predictive value was lower (48-79%). Sensitivity of direct smear was considered as low and varied from 24 to 46% for tracheal brushings and from 41 to 46% for tracheal washings. Specificity of direct smear was high for both types of specimens. Results of this study indicate that the use of Gram-stained smear examination, carried out on tracheal secretions, is a technique which is specific but not very sensitive for the prediction of bacteriological culture results. Moreover, the use of tracheal washing, more than tracheal brushing, seems to increase the sensitivity of the test.