The epidemiology of interstitial lung diseases

Little epidemiologic data are available on the occurrence of interstitial lung diseases (ILDs) in the general population. To describe the prevalence and incidence of ILDs a population-based registry of patients with ILDs was established in Bernalillo County, New Mexico in October 1988. All patients 18 yr of age and older who had a clinical diagnosis of an ILD were identified during the period 10/1/88 through 9/30/90 from physician referrals, hospital discharge diagnoses, histopathology reports, and death certificates. In addition, the prevalence of preclinical or undiagnosed cases was identified by screening lung specimens from 510 autopsy cases. A total of 2,936 referrals were screened; 8.8% were prevalent cases and 6.9% were incident cases. Overall, the prevalence of ILDs was 20% higher in males (80.9 per 100,000) than in females (67.2 per 100,000). Similarly the overall incidence of ILDs was slightly more common in males (31.5 per 100,000/year) than females (26.1 per 100,000/year). The estimated prevalence of preclinical or undiagnosed ILDs among all deaths was 1.8%. The most common incident diagnoses among both sexes were pulmonary fibrosis and idiopathic pulmonary fibrosis, together accounting for 46.2% of all ILD diagnoses in males and 44.2% in females. We conclude that the occurrence of ILDs in the general population may be more common than previous estimates based on selected populations, and these disorders may frequently be unrecognized.