Outbreak of Post‐Infectious Bronchiolitis Obliterans (PIBO) After Adenovirus Infection: A Case Series and Review of the Literature

BACKGROUND: Post-infectious bronchiolitis obliterans (PIBO) is a rare chronic pediatric pulmonary disease characterized by irreversible fibrotic narrowing of the small airways. Treatment options remain uncertain with limited success. OBJECTIVE: To delineate the characteristics of patients diagnosed with PIBO in Ljubljana (Slovenia) and Trieste (Italy) in 2023. METHODS: We retrospectively assessed clinical records of PIBO patients from January to December 2023, capturing data on initial viral infection, clinical presentation, radiological features, treatments, and outcomes. RESULTS: In 2023, 11 patients were identified, contrasting with only 6 cases in the previous 7 years. Common symptoms and signs included tachypnea, chronic wet cough, and diffuse crackles following adenovirus pneumonia. Most patients were previously healthy. Chest CT findings confirmed the diagnosis in all cases. Bronchoalveolar lavage showed elevated levels of neutrophils (46% to 90% of cells), and biopsies performed in 6 patients indicated predominantly lymphocytic inflammatory infiltrate and bronchiolar fibrosis. Nocturnal pulse oximetry revealed reduced mean SpO2 (median: 96.5% Q1: 93%, Q3: 98%) and reduced lower values (median: SpO2 89% Q1: 87%, Q3: 92.5%) with an increased oxygen desaturation index (1.1 to 11.2 events/hour). Treatment involved methylprednisolone (20-30 mg/kg) for three consecutive days monthly for 6 months, resulting in clinical improvement in nine patients and radiological improvement in seven patients. CONCLUSIONS: The post-pandemic surge in PIBO cases may stem from viral ecology changes, immunologic factors, and/or adenovirus genotypes, highlighting the need for further research into its etiology and management strategies.