Neutrophils are involved in the development and outcomes of plastic bronchitis associated with Mycoplasma pneumoniae pneumonia.

BACKGROUND: Previous research has demonstrated a notable increase in neutrophil counts among pediatric patients with plastic bronchitis (PB) associated with Mycoplasma pneumoniae pneumonia (MPP). However, the role of neutrophils in MPP-associated PB remains largely elusive. METHODS: This is a nested case-control study that enrolled patients diagnosed with MPP who underwent bronchoscopy in our department during the MPP pandemic from September 2023 to January 2024. We conducted an analysis of clinical characteristics, blood samples, bronchoalveolar lavage fluid (BALF), and cast specimens, correlating these factors with the development and outcomes of PB. RESULTS: Among the 557 patients with MPP included in the study, 21 (3.8%) developed PB. The peripheral neutrophil count was identified as an independent risk factor for PB (OR = 3.113 [95%CI 1.050-9.224], P = 0.04) and exhibited strong predictive value for the condition (AUC = 0.885 [95%CI 0.796-0.975], P < 0.001). Notably, there was a marked presence of neutrophil infiltration and neutrophil extracellular traps (NETs) formation in the blood, BALF, and cast samples from patients with PB. Furthermore, the levels of neutrophils and NETs correlated significantly with clinical outcomes. CONCLUSION: A high level of neutrophils poses a risk for PB and demonstrates strong predictive value for its diagnosis. Neutrophils and NETs are closely linked to the clinical outcomes of PB in patients with MPP.