Psychological First Aid (PFA) is currently the most recommended early intervention for people affected by recent traumatic events, especially in the aftermath of natural disasters. Unfortunately, there is no evidence that PFA neither prevents Post-Traumatic Stress Disorder (PTSD) nor other post-traumatic disorders or symptoms of distress. This project aims to evaluate the efficacy and safety of Psychological First Aid for the prevention of PTSD and other post-traumatic disorders or symptoms.

Background: Psychological First Aid (PFA) is currently the most recommended early intervention for people affected by recent traumatic events, especially in the aftermath of natural disasters. Unfortunately, there is no evidence that PFA neither prevents Post-Traumatic Stress Disorder (PTSD) nor other post-traumatic disorders or symptoms of distress.

Objective: This project aims to evaluate the efficacy and safety of Psychological First Aid for the prevention of PTSD and other post-traumatic disorders and/or symptoms.

Population: Investigators will perform a 1:1 randomized-controlled trial of 200 adults recently affected (<=72 hours) by a non-intentional trauma who consult to the emergency room of a public hospital. Investigators estimated a sample size of 200 individuals in order to detect a 50% Relative Risk Reduction (RRR), with a power of 80%, a statistical significance (alpha) of 5% and 34,4% of PTSD prevalence in the control group, what is consistent with prevalences observed in a similar sample by Fullerton, Ursano, Epstein, Crowley, Vance et al. (2001).

Intervention: In the emergency room, undergraduate psychology students, previously trained and certified in PFA, will search and randomize suitable patients to either PFA or treatment as usual (TAU). They will provide PFA according to a protocol based on the WHO PFA Operation Guide to those patients included in the active group. Everyone correctly randomized will be followed and clinically evaluated one month after the intervention (endpoint).

Inclusion Criteria:

• Adults (≥ 18 years old) concurring to the emergency room, either as a patient himself or companion, who have been victims of a recent unintentional trauma (less than 72 hours ago), and meet one of the following criteria:
• Direct victim, as a family or as a witness, of a situation that was or is currently life threatening.
• Direct victim, as a family or as a witness, of a situation that affected or currently seriously endangers the physical integrity.

For example, such situations include serious accidents, catastrophic illness, highly painful medical procedures, bad medical news, natural disasters, fires, witnessing another person violent death, explosions, among others.

Exclusion Criteria:

• Does not understand Spanish
• Child and adolescent (< 18 years old)
• Can not remember traumatic experience recently experienced
• Psychosis (loss of reality testing)
• People in life-threatening or health instability situation, requiring equipment for life support incompatible with this application protocol (serious fractures, severe bleeding wounds with uncontrolled excruciating pain, unstable myocardial infarction, etc.). Will be the attending physician whom inform the patient if this exclusion criterion is met.
• Relatives of people in imminent life-threatening or recently died in the emergency room where the offer to participate in the research can cause even greater discomfort.
• Impairment of consciousness (Glasgow < 15)
• Intoxication
• Loss of consciousness for more than 5 minutes.
• Direct and indirect victims of intentional trauma (eg. assault, kidnapping, sexual abuse, terrorist attack, etc).
• Patients being treated for a psychiatric disorder diagnosed by a doctor (personality disorder is excluded) (eg. schizophrenia, mental retardation, autism, obsessive compulsive disorder, bipolar disorder, depression, Alzheimer's disease, panic disorder, etc.).