Diagnostic limitations of oropharyngeal swab cultures and inconsistent presence of secondary bacterial infection in canine aspiration pneumonia

Objective: In dogs with aspiration pneumonia (AP), our objectives were to determine whether oropharyngeal (OP) swab isolates would match bronchoalveolar lavage fluid (BALF) isolates and determine the frequency of secondary bacterial infection (SBI) in AP by use of 4 definitions. Methods: 30 client-owned dogs with clinical diagnosis of AP (cough or fever, and radiographic alveolar pattern with historical vomiting or regurgitation) with OP and BALF cultures were prospectively enrolled from 2019 to 2023. Exclusion criteria included antimicrobial administration within 14 days of presentation or inability to undergo BALF collection. Definitions of SBI included (1) positive BALF culture (noncontaminant), (2) veterinary criteria (septic inflammation in BALF or nonseptic inflammation with positive culture having ≥ 1.7 × 103 CFU/mL), (3) human criteria (> 7% of cells with intracellular bacteria or positive culture with ≥ 104 CFU/mL), and (4) clinical recovery without antimicrobials. Results: All OP and 16 of 30 BALF cultures were positive, yielding a median of 4 organisms (range, 1 to 6 organisms) and 1 organism (range, 0 to 3 organisms), respectively, with significantly more positive OP isolates. Most OP isolates (91%) were not recovered from BALF. Absence of SBI was documented in 30% to 77% of dogs with AP, depending on definition. Conclusions: OP swabs were polymicrobial, with most organisms (91%) not present in BALF. Many dogs with AP did not meet 1 or more definitions of SBI. Clinical Relevance: Using OP cultures as surrogates for BALF cultures was inappropriate for dogs with AP. Not all dogs with AP had SBI, necessitating further study of when antimicrobial therapy could be avoided versus when it is warranted.