Hypersensitivity Pneumonitis Prevalence in an Insured US Population

Researchers have developed a novel algorithm to identify hypersensitivity pneumonitis.

A novel coding algorithm has been developed using 2004 to 2013 data from MarketScan Commercial and Medicare Supplemental administrative claims that demonstrated both high sensitivity and high specificity for identifying hypersensitivity pneumonitis (HP), with a full description and analysis published in the Annals of the American Thoracic Society. The validity and reliability of the algorithm were evaluated using clinical data from National Jewish Health in Denver, Colorado.

With limited data available on the epidemiology of HP, the investigators sought to describe the trends related to annual incidence and prevalence of HP in the United States. A total of 7498 cases that met the researchers’ definition of HP were identified during the 10-year study period, which included 3902 patients with chronic HP and 1852 with fibrotic HP. Based on the clinical-radiologic adjudication of the validation sample, 38 cases were confirmed as HP. Mean patient age was 52 years; 58% were women.

The 1-year prevalence rates of HP ranged from 1.67 to 2.71 per 100,000 persons. Moreover, the 1-year cumulative incidence rates of HP ranged from 1.28 to 1.94 per 100,000 persons. The prevalence of HP was shown to increase with age, with rates of 0.95 per 100,000 persons reported in those between 0 and 9 years of age, rising to 11.2 per 100,000 persons in those ≥65 years of age.

Overall, 50% to 63% of all HP cases reported each year were categorized as being chronic HP (prevalence: 0.91-1.70 per 100,000 persons; cumulative incidence: 0.63-1.08 per 100,000 persons). In contrast, there were fewer cases of fibrotic HP reported (prevalence: 0.41-0.80 per 100,000 persons; cumulative incidence: 0.29-0.43 per 100,000 persons). A majority of the HP cases (74%) were labeled as unspecified HP. In unadjusted analyses, male sex, older age, and the presence of fibrosis were all shown to be linked with higher mortality rates in patients with HP.

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The investigators concluded that based on their novel algorithm, between 2004 and 2013, HP was more common in women and individuals >65 years of age. Many cases of HP were classified as being chronic in nature, and approximately one-quarter of all cases were considered to be fibrotic, which was associated with higher death rates. The findings of this analysis underscore the importance of prevention and the need for effective targeted pharmacologic treatments in this patient population.


Fernández Pérez ER, Kong AM, Raimundo K, Koelsch TL, Kulkarni R, Cole AL. Epidemiology of hypersensitivity pneumonitis among an insured population in the United States: a claims-based cohort analysis. Ann Am Thorac Soc. 2018;15(4):460-469.