Abstract Introduction Post-infectious bronchiolitis obliterans (PIBO) is a rare chronic lung disease that occurs following a respiratory tract infection. Most prior reports are from outside the U.S. Our objective is to describe clinical characteristics of PIBO participants enrolled in the U.S. Registry for Childhood Interstitial and Diffuse Lung Diseases (ChILD). Methods We identified children with PIBO based on diagnosis by a pediatric pulmonologist. Data elements were collected from the US ChILD Registry REDCap forms. Variables are reported as median with interquartile range (IQR). Results Seventy-four participants were diagnosed with PIBO between 2005-2025 from 21 pediatric centers, with median age of 2.3 yrs (IQR: 1.0 - 6.1) at time of infection, 4.0 years (IQR: 1.9 - 9.3) at diagnosis, and 11.3 years (IQR: 7.6 - 16.8) at follow-up data entry (Figure 1A). All participants were alive, and 2 underwent lung transplant. Sixty-four participants (86%) had an identified sentinel infection reported. Infectious etiologies included adenovirus (33; 51.6%), respiratory syncytial virus (RSV) (12; 18.8%), mycoplasma pneumoniae (8; 12.5%), others (32, 50.0%), and sometimes multiple (9; 14.1%). Nearly all (62/64; 96.8%) required hospitalization. Respiratory support included supplemental oxygen (44, 68.8%), non-invasive (27, 42.2%) or invasive mechanical ventilation (19, 29.7%), and extracorporeal membrane oxygenation (7, 10.9%). All participants manifested with ≥1 common PIBO finding on chest CT, including mosaic attenuation, ground glass opacities, or air trapping, and the majority (52/74, 70.3%) also demonstrated bronchiectasis. Nineteen (25.7%) underwent lung biopsy, while 55 (74.3%) were diagnosed by clinical and radiographic features alone. Initial spirometry demonstrated severe impairment, median FEV1: 52.0% (38.0 - 71.5%) (Figure 1B). Severity of illness scores decreased over the first year following diagnosis, from 51.3% to 32.4% of subjects with scores ≥3 (Figure 1C). Inhaled steroids (49, 66.2%), azithromycin (50, 67.6%), montelukast (41, 55.4%) and systemic steroids (47, 63.5%) were common treatments reported, while only 6 (8.1%) reported ongoing systemic steroid therapy (Figure 1D). Conclusions This study is the largest multi-center cohort of children with PIBO in the U.S. Spirometry demonstrated severe impairment as in prior published PIBO cohorts, however ages at infection and diagnosis were older in this U.S. cohort. Clinical scoring improved within the first year after diagnosis, without further improvement, emphasizing a potential critical window for intervention. Additional studies characterizing trajectories based on PIBO phenotype remain underway. This cohort provides a clinical benchmark for the natural history of children with PIBO in the U.S. that may guide future therapies to prevent impairment. This abstract is funded by: NIH NIEHS R01ES037260
McGraw et al. (Fri,) studied this question.