BackgroundThe Pneumonia Severity Index (PSI) and the CURB-65 score assess disease severity in patients with community acquired pneumonia (CAP). We compared the clinical performance of both prognostic scores according to clinical outcomes and admission rates.MethodsA nationwide retrospective cohort study was conducted using claims data from adult CAP patients presenting to the emergency department (ED) in 2018 and 2019. Dutch hospitals were divided into three categories: “CURB-65 hospitals” (n=25), “PSI hospitals” (n=19) and hospitals using both (“no-consensus hospitals”, n=15). Main outcomes were hospital admission rates, intensive care unit admissions, length of hospital stay, delayed admissions, readmissions and all-cause 30-day mortality. Multilevel logistic and Poisson regression analysis were used to adjust for potential confounders.FindingsOf 50.984 included CAP patients, 21.157 were treated in CURB-65 hospitals, 17.279 in PSI hospitals and 12.548 in no-consensus hospitals. The 30-day mortality was significantly lower in CURB-65 hospitalsversusPSI hospitals (8·6% and 9·7%, adjusted odds ratio (aOR) 0·89, 95% CI: 0·83–0·96, p=0·003). Other clinical outcomes were similar between CURB-65 hospitals and PSI hospitals. No-consensus hospitals had higher admission rates compared to the CURB-65 and PSI hospitals combined (78·4% and 81·5%, aOR 0·78, 95% CI: 0·62–0·99).InterpretationIn this study, using the CURB-65 in CAP patients at the ED is associated with similar and possibly even better clinical outcomes compared to using the PSI. After confirmation in prospective studies, the CURB-65 may be recommended over the use of the PSI since it is associated with lower 30-day mortality and more user-friendly.