Incidence, prevalence, and clinical course of idiopathic pulmonary fibrosis: a population-based study

Abstract

Background: Limited data exist regarding the population-based epidemiology of idiopathic pulmonary fibrosis (IPF). The objective of the study was to describe the trends in the incidence, prevalence, and clinical course of IPF in the community.

Methods: We conducted a population-based study of adult patients with IPF in Olmsted County, Minnesota, from 1997 to 2005. Two methods were used to identify IPF cases, as defined by the 2002 American Thoracic Society/European Respiratory Society consensus statement: (1) usual interstitial pneumonia (UIP) on a surgical lung biopsy specimen or a definite UIP pattern on a high-resolution CT image (narrow criteria) and (2) UIP on a surgical lung biopsy specimen or a definite or possible UIP pattern on CT image (broad criteria).

Results: Of 596 patients screened for the possibility of pulmonary disease or pulmonary fibrosis over 9 years of follow-up, 47 cases had IPF. Of these, 24 met the narrow criteria. The age- and sex-adjusted incidence was 8.8/100,000 and 17.4/100,000 person-years, for narrow and broad criteria, respectively. The age-adjusted incidence was higher in men than in women, and among patients aged 70-79 years. During the study period, the incidence of IPF decreased (P < .001). On December 31, 2005, the age- and sex-adjusted prevalence was 27.9/100,000 and 63/100,000 persons by narrow and broad criteria, respectively. Thirty-seven patients experienced a total of 53 respiratory exacerbations (26 IPF related, 27 non-IPF related), and 34 (72%) patients died. The primary cause of death was IPF related in 16 (47%) patients. Median survival for narrow-criteria and broad-criteria incidence cases was 3.5 and 4.4 years, respectively.

Conclusions: The incidence of IPF in Olmsted County decreased over the study period. Nonprimary IPF respiratory exacerbations are as frequent as primary IPF respiratory exacerbations and an important cause of death.

Figures

Figure 1.

Olmstead County records-linkage system.

Figure 2.

Incidence rate of IPF adjusted to 2000 US white population per 100,000 person-years among residents of Olmstead County, Minnesota, from 1997 to 2005. Age-adjusted (A) and age-adjusted and sex-adjusted (B) incidence of narrow criteria cases of IPF with confidence intervals (N = 24). Age-adjusted (C) and age-adjusted and sex-adjusted (D) incidence of broad criteria cases of IPF with confidence intervals (N = 47). IPF = idiopathic pulmonary fibrosis.

Figure 3.

Projected number of individuals with IPF in the United States between 2005 and 2050, assuming no further increase in age-adjusted IPF incidence rate, as evident in 2003 to 2005. See Figure 2 legend for expansion of the abbreviation.

Figure 4.

Observed and expected cumulative survival of patients from time of IPF diagnosis, between 1997 and 2005, among residents of Olmstead Country, Minnesota. Narrow criteria cases of IPF (log rank, P < .0001) (A). Broad criteria cases of IPF (log rank, P < .0001). See Figure 2 legend for expansion of the abbreviation.