Application of bronchoalveolar lavage fluid cytomorphology in diagnosing Nocardia otitidiscaviarum: a case report

Nocardiosis is a rare infectious disease, which is frequently underdiagnosed because of the distinct bacterial shape of the causative agent and its developmental history. The morphological analysis of bronchoalveolar lavage fluid can facilitate the detection of pathogenic bacteria by observing cellular–bacterial interactions.

An immunocompetent 67-year-old male patient of Asian ethnicity developed a cough without apparent cause 20 days earlier. We initially discovered mycobacteria that appeared to be Nocardia in the cytomorphological examination of bronchoalveolar lavage fluid, which was later determined to be Nocardia otitidiscaviarum through metagenomic next-generation sequencing and microbiological cultures. The patient was eventually diagnosed with Nocardia pneumonitis after other testing and clinical signs were considered. After anti-infective treatment, the patient improved and was discharged.

Several diagnostic approaches were used in this case, and the importance of cell morphology as an early screening method was emphasized for suspected Nocardia infection.