Outcome prediction in elderly aspiration pneumonia despite broad-spectrum antibiotic therapy Running title: Prognostic Score for Elderly Aspiration Pneumonia

In older patients with aspiration pneumonia, poor outcomes despite broad-spectrum antibiotic therapy may be more strongly associated with host vulnerability than with pathogen-related factors. This study aimed to develop and validate a prognostic score for in-hospital mortality in older patients with aspiration pneumonia receiving broad-spectrum antibiotics. We analyzed nationwide data from the Diagnosis Procedure Combination database for patients aged ≥ 65 years who were hospitalized with aspiration pneumonia in Japan between January and December 2018 and received antipseudomonal antibiotics within three days of admission. Eligible patients were randomly divided into derivation and validation cohorts. Predictors of in-hospital mortality were identified using multivariable logistic regression, and a prognostic score was developed. Among 13,340 patients, 2,511 (18.8%) died during hospitalization. Age ≥ 85 years, male sex, body mass index < 18.5 kg/m², Barthel Index < 70, impaired consciousness, poor Hugh-Jones classification, chronic heart failure, interstitial pneumonia, renal failure, and malignancy were independently associated with in-hospital mortality. The score showed similar discrimination in the derivation and validation cohorts, with AUCs of 0.650 and 0.652, respectively. This score may help identify older patients with aspiration pneumonia who remain at high risk of in-hospital mortality despite broad-spectrum antibiotic therapy.