Outbreak of Post-infectious Bronchiolitis Obliterans (PIBO) post adenovirus infection. A case series and review of the literature

Post-infectious Bronchiolitis Obliterans (PIBO) is a rare chronic pediatric pulmonary disease often engaged by adenovirus and characterized by non-reversible narrowing of the small airways due to fibrosis. Treatments are uncertain, with limited success. We performed a retrospective study in Ljubljana (Slovenia) and Trieste (Italy) identifying 11 cases of PIBO from January 2023 to December 2023. On average we encountered one case of PIBO per year at our centres over the previous 7 years. All patients presented, wheezing, polypnoea (median respiratory rate 28 apm), chronic productive cough and diffuse crackles more pronounced in most of the cases at the right anterior part of the chest. Previously they were healthy children in all but one case. Chest computed tomography (CT) was consistent with the diagnosis. Bronchoalveolar lavage was performed in 8 patients revealing neutrophilia ranging from 46 to 90% of cells. Eight patients were found colonized by bacteria (6 H influenzae), and five by viruses (1 adenovirus). Biopsies were performed in 7 finding mixed inflammatory interstitial infiltrate (neutrophilic and lymphocytic) and chronic bronchitis. In 8 patients nocturnal pulse oximetry was performed showing a reduced average SpO2 (median 96.5%) and lower values (median minimum SpO2 89%). The oxygen desaturation index varied from 1.1 to 11.2 events/hour. All patients received monthly corticosteroid pulses 20-30 mg/kg up to 1 gr for three consecutive days for 6 consecutive months (median 6, Q1 3.75, Q3 6 months). Clinical and CT improvement occurred in 6 patients, while others had persistent symptoms and pulmonary exacerbations. This unprecedented rise in PIBO cases after the pandemic may be due to changes in viral ecology, immunologic debt and/or adenovirus genotypes.