Incidence, comorbidity and survival rate of hypersensitivity pneumonitis: A population-based study

Abstract

Introduction: Hypersensitivity pneumonitis (HP) is a rare interstitial lung disease (ILD), with an almost undescribed lethality. Very few studies have investigated HP on a national level. Aim: The aim of this study was to investigate incidence, survival rate and comorbidity of this disease nationwide in Denmark. Methods: Using the Danish National Patient Registry we identified all patients with a first-time diagnosis of HP between 1998 and 2010. Patients with HP were matched 1:4 with controls by gender, age, marital status and geography. Co-morbidity three years prior to diagnosis was explored by the Charlson index score. Survival rates were assessed using Kaplan-Meier curves and Hazard Ratios. Results: We identified 753 patients (men: 56.7%) during the observation period and an average HP-incidence of 63 pr. Year. More than half (388 patients = 51.5%) was below 50 years. Survival rates of HP were lower at all time points when compared to the matched control population. The highest mortality among patients with HP was observed during the first two years following initial diagnosis - revealing a higher mortality rate in the age groups 0-39 and 60-80+. Furthermore, patients had a significant higher Charlson index score when compared to the matched controls (0.2 vs 0.008; p Conclusion: For the first time ever, national, longitudinal data regarding age at diagnosis, incidence, hospital contacts, co-morbidity and the mortality rate of HP are presented. We found an increased mortality among HP patients compared with a matched control group without HP. This might indicate, that this rare disease should be centralized to a few centers with high expertise in treatment modalities.