With increasing numbers of previous traumatic experiences, a rising risk of psychiatric morbidity and in particular post-traumatic stress disorder following an acute trauma has been reported. This dose-effect relationship was called the building block effect. Most results are derived from studies on riot and prosecution victims. We investigated victims of a natural disaster with respect to the building block effect due to prior traumatization.

We assessed tourists who had been affected by the Indian Ocean Tsunami 2004 using the Post-traumatic Diagnostic Scale, the Hospital Anxiety and Depression Scale, and the Post-traumatic Growth Inventory. Outcome variables were related to the numbers or prior civil trauma according to the trauma history scale of the PDS.

We found a building block effect for the development of anxiety (P = 0.018) and by trend with PTSD symptoms (P = 0.06), but not with depressive symptoms (P = 0.436). Prior traumatization and the actual Tsunami exposure significantly explained variance of personal posttraumatic growth (P = 0.013). Prior interpersonal traumata emerged as a strong risk factor for the development of posttraumatic psychiatric morbidity.

We suggest that an increasing number of trauma is closely associated with anxiety but not with depressive disorders in the aftermath of natural disasters. For clinical practice, it is necessary to ask victims of natural disasters about prior traumatization, in particular about prior interpersonal trauma.

The authors have not supplied their declaration of competing interest.