The lingering effect of prior critical incidents on today's operational work among ambulance workers: A longitudinal study.

OBJECTIVE: Accumulation of multiple trauma exposure has been linked to sensitization toward developing posttraumatic stress symptoms (PTSS). However, it remains unknown whether the frequency of critical incidents in the past continues to affect ambulance personnel over time. This study investigates whether the frequency of exposure to critical incidents in the past year is associated with higher PTSS levels at baseline, whether this effect persists at 12-month follow-up, and whether the emotional intensity of the most severe incident moderates the association. METHOD: A longitudinal survey study was conducted with 451 ambulance workers. Linear mixed models were utilized to analyze the associations between exposure to critical incidents in the past year and PTSS levels at baseline and at 3-, 6-, 9-, and 12-month follow-up. RESULTS: There was a positive association between frequency of critical incidents and PTSS levels, showing a dose-response pattern. PTSS declined across all groups over time, though less markedly among those with high exposure. An interaction between frequency and emotional intensity was found; the association between frequency and PTSS persisted only in those reporting high emotional intensity during the worst incident. CONCLUSIONS: There was a significant association between frequency of exposure and PTSS over 12 months but only for those experiencing high emotional intensity. This association remained significant when adjusting for covariates and new exposures. To understand posttraumatic stress disorder development in ambulance work, it is important to acknowledge past exposure with a focus on the interaction between a high frequency of critical incidents and the emotional intensity experienced. (PsycInfo Database Record (c) 2026 APA, all rights reserved).