Association of body mass index with Clostridioides difficile infection among older patients with pneumonia in Japan.

AIM Obesity is reported to be a risk factor for Clostridioides difficile infection. However, obesity rarely occurs in older Asian patients, and the effects of obesity on health and disease are different in Asian and Western countries. This study aimed to assess the association between body mass index and C. difficile infection risk among older patients with pneumonia in Japan. METHODS This retrospective observational cohort study used data from the nationwide database of acute hospital inpatients' data in Japan between July 2014 and March 2016. All patients aged ≥65 years admitted with a primary diagnosis of pneumonia were enrolled. Risk factors for C. difficile infection were determined by logistic regression analysis, including known risks as covariates. RESULTS Among 221 242 pneumonia patients, 611 developed C. difficile infection. Underweight patients (body mass index <18.5 kg/m2 ) showed higher odds for C. difficile infection (odds ratio 1.38, 95% confidence interval 1.17-1.62, P < 0.001) than normal weight patients (body mass index 18.5-24.9 kg/m2 ), whereas overweight patients (body mass index ≥25 kg/m2 ) showed lower odds (odds ratio 0.63, 95% confidence interval 0.45-0.89, P < 0.01). CONCLUSIONS Body mass index was associated with C. difficile infection in older pneumonia patients in Japan. Underweight was a risk factor, whereas overweight was a protective factor for C. difficile infection. Geriatr Gerontol Int 2021; ••: ••-••.