Database analysis of hypersensitivity pneumonitis in Japan.

Background: Three epidemiological small-scale studies on hypersensitivity pneumonitis (HP) have been performed in Japan to date. Herein, we aimed to clarify the clinical characteristics of various types of HP diseases using a large nationwide database in Japan.
Methods: We used the Japanese Diagnostic Procedure Combination database that includes data from 1,031 participant hospitals. Patients with HP from 2011 to 2017 were identified using International Classification of Diseases 10th Revision codes. We analyzed patient characteristics, the yearly transition of the number of HP cases, rate per one million hospitalizations, geographical distribution, seasonality, and risk factors for in-hospital mortality.
Results: In total, 3,634 patients with HP were identified, including summer-type HP (SHP) (n = 490), bird fancier's lung (BFL) (n = 199), ventilation pneumonitis (n = 106), farmer's lung (n = 48), and unspecified HP (n = 2761). The length of hospital stay was significantly longer in patients with BFL (19 days) than in patients with SHP (15 days). SHP was more prevalent in the southwestern region of Japan, and hospitalization occurred mainly in summer (37.8%) and fall (37.3%). Ventilation pneumonitis was predominant in winter (28.6%) and spring (38.7%). In-hospital mortality was significantly associated with old age (p < 0.001), low body mass index (p = 0.016), severe dyspnea (p < 0.001), and BFL diagnosis on admission (p = 0.031).
Conclusions: This study revealed the clinical characteristics of SHP and BFL, including the frequency of causative antigens, geographical distribution, seasonality, and risk factors for mortality, which may help in diagnosing HP and identifying causative antigens.
Competing Interests: Conflict of Interest This study has received a Grant-in-Aid for Research on Policy Planning and Evaluation from the Ministry of Health, Labour and Welfare, Japan (20AA2005). Tsukasa Okamoto has received grants from Konica Minolta, Boehringer Ingelheim, Chugai, Kuramochi Clinic and Wako Filter Technology. Yasunari Miyazaki has received grants, consulting fees and payment for lectures and expert testimony from Thermo Fisher Scientific Inc. Shohei Yamashita, Tatsuo Kawahara, Tomoya Tateishi, Tatsuhiko Anzai, Kunihiko Takahashi and Kiyohide Fushimi have no conflict of interest to declare.
(Copyright © 2023 The Japanese Respiratory Society. Published by Elsevier B.V. All rights reserved.)