Guideline-Concordant Antibiotic Treatment for Hospitalised Patients with Community-Acquired Pneumonia and Clinical Outcomes at a Tertiary Hospital in Australia

<b>Background/Objectives:</b> Community-acquired pneumonia (CAP) remains a major cause of hospitalisation and death, particularly among older and frail adults. Although treatment guidelines exist, adherence to empiric antibiotic recommendations is variable. This study examined whether receiving guideline-concordant antibiotics for CAP was associated with better short- and long-term clinical outcomes. <b>Methods:</b> We conducted a retrospective cohort study of adults admitted with radiologically confirmed CAP to a tertiary hospital in Australia from 1 January to 31 December 2023. Patients with hospital-acquired pneumonia or COVID-19 were excluded. Antibiotic concordance was assessed against local guidelines. Propensity score matching (PSM) accounted for 16 covariates including age, comorbidities (Charlson Index), frailty (Hospital Frailty Risk Score), and pneumonia severity (SMART-COP). Primary outcomes were in-hospital, 30-day, and one-year mortality. Secondary outcomes included ICU admission, invasive ventilation, vasopressor use, hospital length of stay, and 30-day readmissions. <b>Results:</b> Of 241 patients, 51.4% received guideline-concordant antibiotics. Mean age was 73.5 years; 50.2% were male; 42.2% had severe pneumonia (SMART-COP ≥ 5); 36.5% were frail. In unadjusted analysis, in-hospital mortality was higher in the concordant group (5.6% vs. 0.9%, <i>p</i> = 0.038). After PSM (n = 105 matched pairs), concordant treatment was associated with significantly lower 30-day mortality (coefficient = -0.12; 95% CI: -0.23 to -0.02; <i>p</i> = 0.018) and there was a non-significant trend towards reduced 1-year mortality (<i>p</i> = 0.058). Other outcomes, including in-hospital mortality, were not significantly different. <b>Conclusions:</b> Guideline-concordant antibiotics were associated with reduced 30-day mortality in CAP. These results support adherence to evidence-based treatment guidelines to improve patient outcomes.