Diagnostic turnaround time and antimicrobial use in suspected central nervous system infection: a regional Australian cohort study

Background: Timely microbiological diagnosis is central to antimicrobial stewardship in suspected central nervous system (CNS) infection. In regional settings, access to rapid diagnostics may be limited by off-site testing and reporting delays. We evaluated the association between multiplex polymerase chain reaction (PCR) turnaround time and antimicrobial use and hospital length of stay (LOS). Methods: We conducted a retrospective cohort study of adult patients (≥18 years) undergoing lumbar puncture for suspected meningitis or encephalitis at two regional Australian hospitals in 2022. Data included time from lumbar puncture to PCR result, antibacterial and antiviral duration and days of therapy (DOT) and LOS. Associations were assessed using Spearman correlation and non-parametric tests. Results: Longer PCR turnaround time was associated with increased antibacterial (rho = 0.22, P = 0.012) and antiviral duration (rho = 0.38, P < 0.001). Median antibacterial duration was 2.2 days (range 0.16–10.49) and antiviral duration 2.52 days (range 0.22–21.35). Median LOS was 4.98 days (range 0.38–92.92). Median turnaround time was 44.8 hours (range 15.1–117.22). Overall, 117 patients received antibacterial therapy (median DOT 3 days, range 1–28) and 84 received antiviral therapy (median DOT 3 days, range 1–22). LOS correlated with antimicrobial duration (rho = 0.22, P = 0.012). Conclusions: Delayed PCR reporting was associated with longer antimicrobial exposure and hospital stay, highlighting diagnostic turnaround time as a potential target for antimicrobial stewardship in regional settings.