BACKGROUND: Chlamydia trachomatis (C. trachomatis) is a common vertically transmitted pathogen responsible for infantile pneumonia, which typically manifests as interstitial lung lesions and pulmonary hyperinflation. Lobar atelectasis resulting from mucus plug obstruction secondary to C. trachomatis infection is rarely observed in children. Here, we report a case of C. trachomatis pneumonia in a 50-day-old full-term male infant presenting with left upper lobe bronchial mucus plugging and atelectasis.

CASE REPORT: A full-term, vaginally delivered 50-day-old male infant presented with a 15-day history of cough and normal oxygenation. Pre-admission imaging showed left upper lobe pneumonia accompanied by atelectasis and bronchial obstruction. Sputum polymerase chain reaction was positive for C. trachomatis, and bronchoalveolar lavage fluid (BALF) targeted next-generation sequencing (tNGS) further supported the etiological diagnosis. The infant was treated with erythromycin combined with bronchoscopic mucus plug clearance, and achieved complete clinical recovery, with no recurrence during 2 months of follow-up.

CONCLUSIONS: In the present case, conventional pathogen detection combined with BALF tNGS supported the diagnosis of C. trachomatis pneumonia associated with secondary airway mucus plugs and lobar atelectasis. Bronchoscopy provided valuable diagnostic and therapeutic benefits in this patient. This case report expands the recognized clinical and imaging spectrum of infantile chlamydial pneumonia and may provide a practical reference for the evaluation of similar atypical pediatric cases.

Keywords: Bronchoscopy, Child, Chlamydia trachomatis, Mucus, Pneumonia, pulmonary atelectasis