Abstract
BackgroundCurrent data on incidence of interstitial lung diseases (ILDs) are sparse and concerns about an increasing trend have been raised. We examined incidence rates (IRs) of ILDs and changes in IRs between 1995 and 2005.MethodsAll persons with a first-time hospital discharge or outpatient diagnosis of ILD were identified through the Danish National Registry of Patients, which covers all Danish hospitals. Crude and age-standardised IRs were computed for ILD overall, as well as stratified by ILD subcategories.ResultsA total of 21,765 patients with ILD were identified. Between 1995 and 1998 the overall standardised IR of ILD decreased from 27.14 (95% CI 25.82–28.46) per 100,000 person-years to 19.36 (95% CI 18.26–20.46) per 100,000 person-years. After 1998 the IR increased considerably, peaking at 34.34 (95% CI 32.84–35.85) per 100,000 person-years in 2002. Subsequently there was a slight decrease. The highest IR was observed in the non-specific category "Respiratory disorders in diseases classified elsewhere". By ILD subcategory, the greatest average increase during the study period was observed in "Respiratory disorders in diseases classified elsewhere".ConclusionThe incidence rate of ILD in Denmark increased during the study period, most pronounced for ILDs associated with systemic diseases.
Highlights
Current data on incidence of interstitial lung diseases (ILDs) are sparse and concerns about an increasing trend have been raised
Since we were interested in the incidence of ILD, we excluded patients diagnosed with ILD in 1994
Overall incidence Between 1995 and 2005, 21,765 patients were registered with a first-time discharge or outpatient diagnosis of ILD
Summary
Current data on incidence of interstitial lung diseases (ILDs) are sparse and concerns about an increasing trend have been raised. Interstitial lung diseases (ILDs) are a heterogeneous group of more than 200 different serious disease entities with common functional characteristics such as restrictive physiology and impaired gas exchange, and with variable degrees of pulmonary inflammation and fibrosis [1,2]. The few previous studies have reported an eightfold variation in ILD incidence, from 3.62 per 100,000 person-years in southern Spain [5] to 31.5 per 100,000 person-years in males and 26.1 per 100,000 person-years in females in New Mexico, USA [6]. Previous European studies of ILD occurrence, based on questionnaires sent to chest physicians, may underestimate the true incidence [5,7,8,9,10]. The only truly population-based study, conducted over 15 years ago, encompassed a relatively small US population of 480,577 and was restricted to a 2-year study period [6]
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