Background: Published data for the epidemiology of idiopathic pulmonary fibrosis in the USA are scarce. We sought to estimate the incidence, prevalence, and mortality risk of idiopathic pulmonary fibrosis among US Medicare beneficiaries.

Methods: We used administrative claims from a 5% random sample of Medicare beneficiaries (aged 65 years and older) from the years 2000-11 as a data source. Idiopathic pulmonary fibrosis was defined by International Classification of Diseases, Ninth Revision, Clinical Modification diagnosis codes. We estimated annual incidence and cumulative prevalence of idiopathic pulmonary fibrosis, median survival time of patients, and potential risk factors for diagnosis of idiopathic pulmonary fibrosis and death between 2001 and 2011. We also estimated incidence and prevalence using more restrictive algorithms for diagnosis.

Findings: The annual incidence of idiopathic pulmonary fibrosis in the Medicare population remained stable between 2001 and 2011, with an overall estimate of 93.7 cases per 100000 person-years (95% CI 91.9-95.4) across the study period. The annual cumulative prevalence increased steadily from 202.2 cases per 100000 people in 2001 to 494.5 cases per 100000 people in 2011. Among newly diagnosed patients with Medicare (mean age 79.4 years [SD 7.2], 54% female, 91% white), the median survival time was 3.8 years (95% CI 3.5-3.8). Older age and male sex were associated with a higher incidence of disease and shorter survival time after diagnosis. Mortality risk was lower in patients diagnosed in more recent years (median survival time 3.3 years [95% CI 3.0-3.8] in 2001 vs 4.0 years [3.8-4.5] in 2007).

Interpretation: The incidence and prevalence of idiopathic pulmonary fibrosis in people aged 65 years and older in the USA are substantially higher than previously reported, and prevalence is increasing annually, even in the subgroups based on more restrictive algorithms for diagnosis. Patients with idiopathic pulmonary fibrosis aged 65 years and older were living longer in 2011 than they were 10 years before, which could partly account for the steady increase in prevalence.

Funding: Biogen Idec.