Epidemiology of idiopathic pulmonary fibrosis: a population-based study in primary care

Idiopathic pulmonary fibrosis (IPF) is a chronic disease with unknown etiology and poor prognosis. Little is known about the epidemiology of this disease; most of the studies are limited by small and restricted cohort studies. We aim to investigate the epidemiology of IPF in the Italian primary care setting using the Health Search Database (HSD) between January 2002 and June 2017. In an attempt to define cases of IPF we adopted iterative combinations of International Classification of Diseases Ninth Revision (ICD-9-CM) and other clinical investigations according to three different operational Algorithms. Incidence and prevalence rate, according to the three Algorithms defining IPF, were calculated and the association with candidate determinants [sex, age, gastro-esophageal reflux (GERD) and smoking status] was evaluated. We identified 1,104,307 eligible patients. The prevalence rate of IPF varies between 2.6 to 24.3 per 100.000 person-year, using algorithm 1 and from 0.8 to 7 using algorithm 3. The incidence rate of IPF varies between 1.25 and 3.77 per 100.000 person-years, using algorithm 1 and from 0.10 to 1.61 using algorithm 3. The mean adjusted incidence rate ratio of IPF, using algorithm 1, is 2.33 (95% CI 2.11-2.57) per 100.000 person-years. Over the study years, the trend of prevalence was statistically significantly increasing while the incidence rate started to increase in the last 3 years. The analyses on candidate determinants showed that patients aged 61 years or older, those suffering from GERD, and former smokers were statistically significantly at greater risk of incurring IPF. To our knowledge, this is one of the first European IPF epidemiological studies conducted in primary care. The increase of the incidence rates is likely due to a growing awareness for IPF among General Practitioners, while the increase of prevalence rates may be due to an increase of survival, a result of recent advances in the diagnosis, management and therapies for the disease.