Abstract
Background: Posttraumatic stress disorder (PTSD) and depression frequently co-occur in adolescents following trauma, but the symptom-level mechanisms underlying this comorbidity remain unclear. The arousal symptoms of PTSD, including sleep problems and other symptoms, are a potential bridging symptom group. This study aimed to investigate the dynamic bridge symptoms linking PTSD and depression among adolescents exposed to a natural disaster, and to examine how these connections evolve over time.Methods: A longitudinal study was conducted with 1,444 adolescents affected by the Zhouqu debris flow. Participants were assessed at 3, 15, and 27 months post-disaster. The University of California at Los Angeles Posttraumatic Stress Reaction Index for Children, revision 1 and the Child Depression Inventory were used to assess PTSD and depression symptoms, respectively. Two cross-lagged panel network (CLPN) models were used to estimate temporal symptom associations and to identify bridge symptoms based on bridge expected influence (BEI).Results: Symptoms in the arousal and reactivity cluster (e.g. sleep disturbance, startle response, concentration problems) exhibited high and stable BEI across two years. However, specific bridge symptoms shifted across phases: startle and irritability were more influential between 3 and 15 months, while concentration problems and anhedonia became more prominent between 15 and 27 months. Network comparison revealed limited structural overlap across time, highlighting stage-specific changes in comorbidity patterns.Conclusions: These findings support a dual-phase mechanism of comorbidity between PTSD and depression. Arousal-related symptoms primarily drive cross-disorder associations in the early stage (3-15 months). In the later stage (15-27 months), depressive symptoms, especially anhedonia, become central, with attentional problems from hyperarousal also contributing. Tailored interventions targeting distinct symptom profiles at different recovery stages (hyperarousal in 3-15 month and anhedonia in 15-27 months) may enhance the effectiveness of post-disaster mental health care.