Age distribution and seasonality in acute eosinophilic pneumonia: analysis using a national inpatient database

BACKGROUND: Acute eosinophilic pneumonia (AEP) is a rare inflammatory lung disease. Previous studies have shown that most patients with AEP are aged 20 to 40 years, whereas several case studies have included older patients with AEP. These studies also suggested that AEP is more prevalent in summer, but they were limited due to their small sample sizes. We therefore investigated the age distribution and seasonality among patients with AEP using a national inpatient database. METHODS: Using the Japanese Diagnosis Procedure Combination database, we identified patients with a recorded diagnosis of AEP from 1 July 2010 to 31 March 2015. We examined patient characteristics and clinical practices including age, sex, seasonal variation, length of stay, use of corticosteroids, use of mechanical ventilation, and in-hospital mortality. RESULTS: During the 57-month study period, we identified 213 inpatients with AEP. The age distribution of AEP peaked twice: at 15 to 24 years and 65 to 79 years. The proportion of patients with AEP was highest in summer for those aged < 40 years, whereas it was distributed evenly throughout the year for those aged ≥ 40 years. The interval from hospital admission to corticosteroid administration and the duration of corticosteroid use were significantly longer in the older than younger age group. CONCLUSIONS: The age distribution of patients with AEP was bimodal, and seasonality was undetected in older patients. Older patients may be more likely to have delayed and prolonged treatment.