Trauma-Related Symptomatology in Horizontal Nurse-to-Nurse Bullying: An Integrative Review of Direct and Indirect Exposure Pathways

AIMS: This integrative review synthesized empirical and conceptual literature on horizontal nurse-to-nurse bullying and trauma-related symptomatology, with particular attention to how secondary traumatic stress has been theoretically conceptualized and operationalized in relation to direct versus indirect exposure pathways. METHODS: Guided by Whittemore and Knafl, an integrative review was conducted. Searches were completed on 6 May 2026 across three databases. Empirical and theoretical studies examining horizontal bullying and trauma-related symptoms in nurses were included. Methodological quality was appraised using Joanna Briggs Institute tools. Data were analyzed using a constant-comparative approach, with reporting aligned to PRISMA 2020. RESULTS: The literature represented over 3,000 nurses across multiple countries. Four themes emerged: (1) measurement-exposure misalignment, with secondary traumatic stress instruments frequently applied to directly victimized nurses despite the construct's grounding in indirect exposure; (2) aggregation of horizontal bullying within broader workplace violence constructs, limiting relational specificity; (3) under-measurement of witnessing, despite its role as a plausible indirect trauma pathway that may intensify symptoms when combined with direct victimization; and (4) contextual vulnerabilities, particularly among novice and critical care nurses. Common limitations included cross-sectional designs, reliance on self-report, and inconsistent definitions of trauma exposure. CONCLUSIONS: Horizontal bullying is associated with trauma-consistent symptom patterns, but conceptual and measurement precision remains limited. Distinguishing direct and indirect exposure pathways, explicitly measuring witnessing, and implementing trauma-informed leadership are critical to protecting nurse well-being and supporting patient safety.