Factors associated with clinical interpretation of tracheal wash fluid from dogs with respiratory disease: 281 cases (2012‐2017)

Abstract

Background: Clinicians face several dilemmas regarding tracheal washes (TWs) for the diagnosis of respiratory disease, including method and prediction of bacterial growth from cytology results. Objective: To compare cytology and culture of endotracheal and transtracheal washes and identify factors associated with discordancy and bacterial growth. Animals: Two hundred forty-five dogs with respiratory disease. Methods: Retrospective study. Tracheal wash submissions were included if cellularity was sufficient for cytologic interpretation and aerobic cultures were performed. Collection technique, cytology, bacterial growth, and antibiotic history were analyzed. Results: Fewer transtracheal specimens (9/144, 6.3%) were excluded for hypocellularity than endotracheal (28/174, 16.1%); otherwise, results were similar and were combined. Of 281 specimens with cellularity sufficient for interpretation, 97 (34.5%) had bacteria on cytology and 191 (68.0%) had bacterial growth. Cytology positive/culture negative discordancy was uncommon (8/97, 8%). Cytology negative/ culture positive discordancy was frequent (102/184, 55.4%), but occurred less often (28/184, 14.2%) when only 1+ growth or greater was considered positive. Oropharyngeal contamination was associated with bacterial growth, but not discordancy. No association was found between antibiotic administration and bacterial growth. Conclusions and Clinical Importance: Endotracheal wash fluid, in particular, should be screened for gross mucus or turbidity to maximize the likelihood of an adequate specimen. Otherwise, endotracheal and transtracheal specimens were similar. Presence of bacteria on cytology was a good predictor of any growth, while their absence was a good predictor of the absence of growth of 1+ or more. Recent antibiotic usage should not discourage TW culture if there is compelling reason to avoid delay.

Antimicrobial resistance profiles of bacteria associated with lower respiratory tract infections in cats and dogs in England

“…A recent study examining TW cytology results from dogs with respiratory disease revealed similar results of discordancy with a high number of cytology negative and culture positive results (55.4%). 33 Pre-treatment with antibiotics may affect cytology results and as no information was provided on the administration of medication to patients before sample collection in our study, this influential factor cannot be excluded. 2,33 In addition, culture of commensal organisms in animals with noninfectious respiratory disease may have also affected these results or even bacteria that are difficult to culture but still detectable on cytology.…”

“…33 Pre-treatment with antibiotics may affect cytology results and as no information was provided on the administration of medication to patients before sample collection in our study, this influential factor cannot be excluded. 2,33 In addition, culture of commensal organisms in animals with noninfectious respiratory disease may have also affected these results or even bacteria that are difficult to culture but still detectable on cytology. One example of this is Mycoplasma spp.…”

“…which are hard to culture but can act as primary pathogens in respiratory infections in cats and dogs. 33,34 Broad-spectrum coverage is recommended for patients suspected of bacterial pneumonia due to the multiplicity of agents that can be involved. 1,2,5,11,16,35 From our laboratory results, amoxicillin-clavulanate showed excellent in vitro activity against B. bronchiseptica and Pasteurella spp., but the levels of susceptibility were however lower in isolates of other bacterial species.…”

Respiratory Diseases and Their Diagnosis in Dogs: A Review

“…The trachea and main stem bronchi constitute a central site of exposure to all inhaled materials and central airway sampling from these sites could enhance the confirmation of airway inflammation (Zhu et al 2015;Graham et al 2021). Tracheal wash aspiration is the minimally invasive procedure which predominantly samples the larger airways along with a certain amount of sample from the lower airways and the alveoli, for cytologic and culture analysis.…”

“…Tracheal wash aspiration is the minimally invasive procedure which predominantly samples the larger airways along with a certain amount of sample from the lower airways and the alveoli, for cytologic and culture analysis. Contributing factors for better sample extraction includes mucociliary clearance and cough reflex (Cohn and Reinero, 2007;Finke, 2013;Graham et al 2021). Cytological interpretation should include estimated cellularity, differential cell counts and morphologic description of the cells encountered (Creevy, 2009).…”