External validation of the PACTO risk score for infective endocarditis in patients with coagulase-negative staphylococcal bacteremia: a multicenter cohort study

Abstract Background Coagulase-negative staphylococci (CoNS) are a leading cause of prosthetic-valve infective endocarditis (IE) and an emerging cause of native-valve IE. Identifying patients with CoNS bacteremia at high risk of IE remains a significant clinical challenge. The PACTO score, derived from a single-center cohort, integrates four early-available predictors of IE. Methods We conducted a multicenter retrospective cohort study of 302 adults with true CoNS bacteremia who underwent echocardiography at several Spanish hospitals between October 2016 and September 2025. IE was diagnosed according to the 2023 Duke-ISCVID criteria. The PACTO score assigns points for prosthetic valve or pacemaker (4), all blood culture bottles positive (2), community-acquired bacteremia (2), and continuous bacteremia (positive cultures 12–72 hours apart; 1). Results Definite IE was diagnosed in 60 patients (19.9%). The PACTO score showed excellent discrimination (AUC 0.828; 95% CI 0.773–0.883) and good calibration (Hosmer-Lemeshow p=0.360). IE prevalence increased progressively across risk categories, from 1.6% (0–1 points) to 84.6% (>7 points). A score <2 points yielded a negative predictive value of 98.4% (sensitivity 98.3%). Conclusions This multicenter external validation demonstrates that the PACTO score provides robust risk stratification for IE in patients with CoNS bacteremia, supporting safe deferral of echocardiography in low-risk patients and prompt imaging in high-risk individuals. Prospective validation is warranted.