Allergology International (Jan 2025)

Estimated prevalence and incidence of hypersensitivity pneumonitis in Japan

  • Tsukasa Okamoto,
  • Mariko Hanafusa,
  • Taketomo Abe,
  • Takashi Shimamura,
  • Masaru Ito,
  • Yoko Wakai,
  • Torahiko Jinta,
  • Katsuyuki Higa,
  • Yasuhiro Kondoh,
  • Yasumi Okouchi,
  • Ryo Okuda,
  • Masashi Bando,
  • Takafumi Suda,
  • Hiromi Tomioka,
  • Takeo Fujiwara,
  • Masato Takase,
  • Shigemi Yoshihara,
  • Hiroshi Odajima,
  • Yasunari Miyazaki

Journal volume & issue
Vol. 74, no. 1
pp. 66 – 71

Abstract

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Background: The latest guidelines on hypersensitivity pneumonitis (HP) categorise the disease as either fibrotic or non-fibrotic because of the greater clinical utility of this stratification. However, the prevalence and incidence of fibrotic and non-fibrotic HP are unknown. This study assessed the exact prevalence and incidence of fibrotic and non-fibrotic HP in Japan in 2021. Methods: For adults, the study hospitals were selected by stratified random sampling according to numbers of beds. The sampling rate was set at about 20%. The questionnaire survey was submitted to the target hospitals. For pediatric cases, a survey was distributed to all members of the Japanese Society of Pediatric Pulmonology and Japanese Society of Pediatric Allergy and Clinical Immunology. Results: Regarding adult cases, in total, 575 facilities responded to the survey, resulting in a response rate of 36.4%. The estimated prevalence and incidence of fibrotic HP were 6.3 and 2.5 per 100,000 population, respectively, versus 3.6 and 2.0 per 100,000 population, respectively, for non-fibrotic HP. Both fibrotic and non-fibrotic HP were more prevalent in southern Japan (Kyushu) and less prevalent in northern Japan (Hokkaido). The incidence of non-fibrotic HP was significantly lower in December than in the other months (relative risk ratio = 0.36, p < 0.001). Three cases of fibrotic HP and five cases of non-fibrotic HP were identified in children. Conclusions: This study determined the prevalence and incidence of fibrotic and non-fibrotic HP in Japan for the first time.

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