Antimicrobial Optimization After Positive Pneumococcal Urinary Antigen Testing in Hospitslized Community-Acquired Peneumonia a Retrospective Cohort Study

Background: Pneumococcal urinary antigen testing (PUAT) rapidly supports pneumococcal etiology in community-acquired pneumonia (CAP), but its impact on antimicrobial optimization in routine care remains uncertain. Objectives: To evaluate antimicrobial spectrum narrowing after positive PUAT in hospitalized adults with CAP and to describe other antimicrobial optimization actions. Methods: We conducted a retrospective observational cohort study at a Portuguese tertiary hospital including adults hospitalized with CAP and positive PUAT between January 2020 and December 2024. The primary endpoint was antimicrobial spectrum narrowing. Absence or early discontinuation of atypical coverage and intravenous-to-oral switch were analyzed separately. Results: Among 332 episodes, antimicrobial spectrum narrowing occurred in 30 (9.0%), after a median of 3 days (Q1-Q3, 2-4). De-escalation to ampicillin or amoxicillin occurred in 7 episodes (2.1%). Narrowing was less frequent among patients initially treated with amoxicillin/clavulanate (10.0% vs 43.7%; p<0.001) and more frequent among those receiving broader-spectrum beta-lactams other than ceftriaxone or amoxicillin/clavulanate (20.0% vs 6.3%; p=0.007). Absence or early discontinuation of atypical coverage occurred in 158 episodes (47.6%) and intravenous-to-oral switch in 71 (21.4%). Narrowing and intravenous-to-oral switch were associated with shorter length of stay, but these associations were considered exploratory because of potential confounding by clinical stability. Conclusions: In hospitalized PUAT-positive CAP, antimicrobial spectrum narrowing was uncommon, whereas atypical coverage optimization was the most frequent prescribing change. Structured reassessment pathways may be needed to translate PUAT results into safe, microbiology-guided antimicrobial optimization.