Clinical characteristics and outcomes of acute eosinophilic pneumonia: A nationwide descriptive study

Acute eosinophilic pneumonia (AEP) is a rare lung disease marked by rapid respiratory failure and eosinophilic infiltration of the lungs. Despite its clinical importance, limited data exist on the characteristics and outcomes of AEP in the general population. We conducted a nationwide study using the Japanese Diagnosis Procedure Combination database from April 2020 to March 2023. Patients with AEP were identified based on diagnostic codes and bronchoscopy records, and we evaluated their clinical characteristics, treatments, and outcomes. A total of 328 patients were included. The median age was 46 years, and 63.7% were male. Hypoxia was present in 86.9% of patients at admission. Systemic corticosteroids were administered to 96% of patients, with 37.5% receiving pulse therapy. Mechanical ventilation was required in 4.9% of cases, and 7.3% of patients were admitted to intensive or high-care units. The median hospital stay was 11 days, and in-hospital mortality was 1.2%. Patients with hypoxia at admission had longer hospital stays and received higher doses of corticosteroids and empirical antibiotics (p < 0.001 for each). No disease-related readmissions were reported after discharge. These findings suggest that most AEP patients have favorable short-term outcomes, although those with hypoxia at admission may require more intensive treatment.