Clinical and prognostic relevance of Mycoplasma felis PCR detection in feline lower respiratory tract disease

Objectives The aim of this retrospective cohort study was to compare two groups of cats with lower respiratory tract disease, one with Mycoplasma felis detected by PCR in the bronchoalveolar lavage fluid (BALF) (M+) and the other without (M-), with regard to signalment, clinical signs, diagnostic results, treatment response and survival.Methods All cats for which M felis was investigated by PCR in BALF between 2016 and 2023 were included. Cats with evidence of oropharyngeal contamination, or for which PCR results were under the quantification level, or without follow-up information were excluded. Cats that had received antibiotics effective against M felis before BALF collection were excluded if PCR results were negative. Follow-up information was retrieved from the medical records and by contacting referring veterinarians and owners.Results A total of 55 cats were included (19 in the M+ group and 36 in the M- group). Significant differences were detected between the two groups in the prevalence of systemic signs (M+: 0%, M-: 28%; P = 0.01), bronchial collapse on bronchoscopy (M+: 28%, M-: 6%; P = 0.03), radiographic alveolar lesions (M+: 57%, M-: 24%; P = 0.04), and percentage of neutrophils (M+: 65%, M-: 35%; P = 0.002) and eosinophils (M+: 9%, M-: 25%; P = 0.03) in the BALF. Antibiotics were used more frequently in M+ cats (M+: 90%, M-: 42%; P = 0.001) than in M- cats. No significant difference was found in treatment response (short term: P = 0.94, long term: P = 0.28) and risk of death (P = 0.42) between the two groups.Conclusions and relevance The presence of radiographic alveolar lesions and neutrophilia in BALF was significantly associated with the detection of M felis in BALF. This association might be causal, consequential or contextual (ie, sharing the same cause). The detection of M felis in BALF did not negatively impact prognosis but the necessity to treat M felis using targeted antibiotics remains to be determined.