Data collection
Patient data were extracted from electronic medical records. Data on patient characteristics such as age, sex, location of residence, underlying comorbidities, body mass index (BMI), A-DROP score, GNRI score, and laboratory test results were collected. The A-DROP scoring system proposed by the Japan Respiratory Society was employed to assess disease severity. The A-DROP score consists of the following items: age  ≥70 years for male individuals and ≥75 years for female individuals, blood urea nitrogen (BUN)  ≥21 mg/dL or dehydration, oxyhemoglobin saturation measured using pulse oximetry ≤90% or partial pressure of oxygen in arterial blood ≤60 mmHg, confusion, and systolic blood pressure ≤90 mmHg. Depending on the number of corresponding items, 0 points was defined as mild, 1–2 points as moderate, 3 points as severe, and 4–5 points as most severe.18 Sputum samples were collected at admission to identify causative pathogens of aspiration pneumonia. They were obtained by expectoration or catheter suction and then cultured. We defined methicillin-resistant Staphylococcus aureus , Pseudomonas aeruginosa , Acinetobacter baumannii ,Stenotrophomonas maltophilia , and extended-spectrum β-lactamase-producing gram-negative bacilli as potential drug-resistant (PDR) pathogens. GNRI was calculated as follows: (14.89 × serum albumin [g/dL]) + (41.7 × [actual body weight/ideal body weight]). Ideal body weight was calculated as: height (cm) – 100 – ([height – 150]/4) for men and height (cm) – 100 – ([height – 150)/2.5] for women. Nutritional risk was determined using GNRI scores, wherein GNRI < 82, 82 ≤ GNRI < 92, 92 ≤ GNRI < 98, and GNRI ≥ 98 indicated severe, moderate, mild, and no risk, respectively.10 We collected data regarding initial antibiotic agents, days of administration, and switching of the initial drug to a different drug. Data on clinical course and outcomes included length of stay (LOS) and in-hospital mortality. The study endpoint was defined as in-hospital mortality. Patients who were discharged were defined as the “survivor group” and those who died during hospitalization were defined as the “non-survivor group.” Patient characteristics, microbiological findings, and clinical course were compared between survivor and non-survivor groups.