Incidence and Prevalence of Idiopathic
Ganesh Raghu, Derek Weycker, John Edelsberg, Williamson Z. Bradford, and Gerry Oster
University of Washington Medical Center, Seattle, Washington; Policy Analysis, Inc., Brookline, Massachusetts; and InterMune Pharmaceuticals,
Rationale: Idiopathic pulmonary fibrosis is a chronic interstitial lung
disease of unknown etiology; its epidemiology in the United States
has not been well characterized.
Objective: To estimate the annual incidence and prevalence of idio-
pathic pulmonary fibrosis in the United States.
Methods: Retrospective cohort design utilizing a large health care
claims database spanning the period January 1996 through Decem-
Measurements and Main Results: Persons with idiopathic pulmonary
fibrosis were identified based on diagnosis and procedure codes.
Using broad case-finding criteria, prevalence was estimated to
range from 4.0 per 100,000 persons aged 18 to 34 yr to 227.2 per
to range from 1.2 to 76.4 per 100,000. Using narrow case-finding
criteria, prevalence ranged from 0.8 to 64.7 per 100,000 persons;
comparable figures for incidence were 0.4 to 27.1 per 100,000 per-
sons. Extrapolating these rates to the overall United States’ popula-
tion, prevalence was estimated to be 42.7 per 100,000 (incidence,
16.3 per 100,000) using broad criteria; with narrow criteria, preva-
lence was estimated to be 14.0 per 100,000 (incidence, 6.8 per
Conclusions: Our results suggest that idiopathic pulmonary fibrosis
is probably more common in the United States than previously
Keywords: epidemiology; lung diseases, interstitial; retrospective
Idiopathic pulmonary fibrosis (IPF) is a progressive life-threat-
ening disease that is characterized anatomically by scarring of
tion and progression are poorly understood (1). Of the over 150
recognized types of interstitial lung disease (ILD), IPF is the
most common and one of the most deleterious (2).
Criteria for the diagnosis of IPF were set forth in an inter-
national consensus statement formulated by members of the
American Thoracic Society (ATS) and the European Respira-
tory Society(ERS) (3). In the absence of biopsy evidence of usual
interstitial pneumonia, a constellation of typical clinical findings
may be used to support the diagnosis of IPF (3). However, the
extentto which these diagnosticguidelines are followed inactual
clinical practice is unknown.
Median survival among persons with IPF is believed to be
from 3 to 5 yr (1, 4–8). Respiratory failure is the most frequent
cause of death, and has been reported to account for over 80%
(Received in original form February 3, 2006; accepted in final form June 13, 2006)
Supported by InterMune, Inc., Brisbane, California.
Correspondence and requests for reprints should be addressed to Ganesh Raghu,
M.D., Division of Pulmonary and Critical Care Medicine, Interstitial Lung Disease,
Sarcoid, and Pulmonary Fibrosis and Lung Transplant Programs, University of
Washington, Seattle, WA 98195-6522. E-mail: firstname.lastname@example.org
Am J Respir Crit Care Med
Originally Published in Press as DOI: 10.1164/rccm.200602-163OC on June 29, 2006
Internet address: www.atsjournals.org
Vol 174. pp 810–816, 2006
of all fatalities; heart failure, bronchogenic carcinoma, ischemic
heart disease, infection, and pulmonary embolism are also com-
mon causes of mortality (9–11). Antiinflammatory, antifibrotic,
and immunosuppressive therapies are often used in the treat-
ment of IPF; however, such treatment has not been demon-
strated to improve survival or quality of life (10, 12).
Surprisingly, little is known about the epidemiology of IPF
in the United States. Initial estimates of its prevalence, based
largely on case series from pulmonary clinics and tertiary-care
hospitals, ranged from 3 to 6 cases per 100,000 persons (13).
Substantially higher rates of prevalence (20 per 100,000 among
men, 13 per 100,000 among women) and incidence (11 and 7
per 100,000, respectively) were reported in a study based on the
adult population of Bernalillo County, New Mexico (14). It is
unclear, however, whether these rates are generalizable to the
present-day United States as a whole, because they are based
on datamore than 15 yrold andcomefroman area ofthe United
States known to attract persons with chronic lung diseases (15).
Although more recent estimates of disease prevalence (range,
1–24 cases per 100,000) are available from several European
studies, their generalizability to the United States is not clear
(16–20). This study used data from a large, geographically di-
verse, United States’ health care claims database to estimate the
prevalence and annual incidence of IPF. Some of the results
from this study have been previously reported in the form of
an abstract (21).
system of a large United States’ health plan, and spanned the period
January 1, 1996, through December 31, 2000. The database consists of
claims for services provided to plan members that were submitted by
facilities (e.g., hospitals), health care professionals (e.g., physicians),
and retail pharmacies. The plan provides health care services—through
health maintenance organizations, preferred provider organizations,
Medicare Risk, and indemnity products—to approximately 3 million
personsintotal residing in20states,mostlyintheSouthAtlantic(28%),
South Central (37%), and North Central (31%) regions of the United
States. Nearly 20% of plan members are aged 65 yr or older.
Data available for each facility and professional-service claim in-
cluded dates and place of service, diagnoses(in International Classifica-
tion of Diseases, 9th revision, Clinical Modification [ICD-9-CM] for-
mat), procedures (in Healthcare Common Procedure Coding System
[HCPCS] format), provider specialty, and reimbursed amounts; profes-
sional-service claims also included information on the number of units
or services provided. Data available for each outpatient pharmacy
claim included the drug dispensed, dispensing date, quantity dispensed,
therapy-days supplied, and reimbursed amounts. Information ondemo-
graphics and eligibility was also available for all plan members. All data
could be arrayed in chronologic order to provide a detailed longitudinal
profile of all medical (inpatient and outpatient) and pharmacy services
used by each plan member.
All patient identifiers in the database had been fully encrypted, and
the database is fully compliant with the Health Insurance Portability
and Accountability Act of 1996 (22). This study is exempt from the
U.S. Department of Health and Human Services’ Federal Policy for
816AMERICAN JOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINE VOL 1742006
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significance of histological classification of idiopathic interstitial pneu-
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APPENDIX 1. ICD-9-CM CODES FOR INTERSTITIAL
LUNG DISEASES OTHER THAN IDIOPATHIC
Other specified disorders of metabolism—includes
Extrinsic allergic alveolitis
Coal workers’ pneumoconiosis
Pneumoconiosis due to other silica or silicates
Pneumoconiosis due to other inorganic dust
Pneumoconiosis due to inhalation of other dust
Chronic respiratory conditions due to fumes or vapors
Chronic and other pulmonary manifestations due to radiation
Respiratory conditions due to other specified external agents
Postinflammatory pulmonary fibrosis
Pulmonary alveolar proteinosis
Idiopathic pulmonary hemosiderosis
Pulmonary alveolar microlithiasis
Other specified alveolar and parietoalveolar
Unspecified alveolar and parietoalveolar pneumonopathies
Lung involvement in systemic sclerosis
Lung involvement in other diseases classified elsewhere
Systemic lupus erythematosus
Sjo ¨gren’s disease
Definition ofabbreviation: ICD-9-CM? International Classification of Diseases,
9th edition, Clinical Modification.