Effect of warm and humid days on the positivity rate of anti-Trichosporon asahii antibody test for the diagnosis of summer-type hypersensitivity pneumonitis

Background: Summer-type hypersensitivity pneumonitis (SHP) has been reported to occur during warm and humid summer seasons in Japan; however, the effect of weather conditions on SHP remains unknown. Anti-Trichosporon asahii antibody (TaAb) test is highly specific and useful for the diagnosing SHP. Therefore, we aimed to investigate the impact of weather conditions on SHP by examining the relationship between the positivity rate of TaAb and warm and humid days.Methods: TaAb test data from June 2013 to June 2020 were obtained from major commercial laboratories to determine the number of samples and positivity rate of TaAb by prefecture. Using the Japan Meteorological Agency database, we counted the warm and humid days (maximum temperature >25 C-degrees and average humidity >= 80 %) for each prefecture. Negative binomial regression was employed to examine the relationship between the positivity rate of TaAb and the number of warm and humid days per month.Results: A total of 79,211 samples and 7626 positive samples (9.6 %) were identified. We found that the number of warm and humid days, 1 or 2 months prior to testing for TaAb, was associated with the positivity rate of the test. An increase in the positivity rate by 1.6 % and 2.9 % was observed with every 1-day increase in warm and humid days 1 month and 2 months before the test, respectively.Conclusions: Our TaAb analysis revealed a significant increase in TaAb positivity 1 or 2 months after periods of warm and humid days.