1.1. Prevalence and Risk Factors
Post-traumatic stress disorder is an outcome that is commonly explored throughout research on terrorism. In the general American and European population, 1-year prevalence is between 0.9–3.5% [
84]. The articles featured in this review identify a higher prevalence of PTSD in individuals both directly and indirectly exposed to terrorist attacks. Given the increase in terrorism research that occurred post 9/11, the majority of the articles featured in this review assessed those populations. In direct survivors, the prevalence of PTSD has been found to be around 30% [
74]. It reaches approximately 39% in the first 6 months, and slowly decreases to about 22% after 1 year [
74]. The prevalence of PTSD without any comorbidities in survivors was found to be about 4.1%, even 14–15 years after the attack [
54]. In traditional relief workers, such as first responders and rescue workers, prevalence for PTSD is lower in the first 3 years, and slowly climbs up to 10%, peaking approximately 5–6 years post-attack [
10,
73]. In non-traditional relief workers, such as volunteer workers, rates of PTSD are much higher, climbing to 21.9% [
10]. The prevalence is about 23% in relatives or close friends of victims who were injured or killed in terrorist attacks [
74].
Though there is not an abundance of articles examining the mental health effects of terrorism set in countries other than the U.S.A., some of these have been reviewed for this article. Certain communities showed higher proportions of PTSD, others lower. However, it can be challenging to compare the prevalence rates given that the level of exposure of the populations studied is heterogenous. In Nairobi, the prevalence of PTSD in survivors and rescue workers following the 1998 U.S. Embassy bombing was 22% which was found to be 2–4 times the rates following the Oklahoma City bombings [
26]. In the 4–6 weeks following the Bardo museum attack in Tunis in 2015, one study found that 68.6% of museum works displayed posttraumatic stress symptoms [
13]. Similarly, 5 months following the Qissa Khwani Bazaar bombing in Pakistan, 77% of direct survivors suffered moderate to severe PTSD [
6]. Following the 2015 Ankara bombings in Turkey, one study found that PTSD prevalence in direct survivors was 24.7% [
12]. In contrast, following the 2011 Oslo bombing, only 2% of trained professionals and 15% of unaffiliated volunteers developed PTSD [
24]. In the first 10 to 34 months, individuals who were directly exposed showed a prevalence of PTSD evolving from 24% to 17%, while for those who were indirectly exposed it went from 4% to 2% [
71]. In France, following the November 2015 Paris terrorist attacks, prevalence amongst resident physicians was 12.4% [
16] and between 3.4–9.5% in other first responders [
44].
Pre-attack risk factors to developing PTSD include being a woman, being of Asian or Hispanic decent (in the American context), having been exposed to a previous terror attack, experiencing a traumatic event in childhood or adulthood, having low social and educational status and having pre-existing psychiatric comorbidities [
8,
13,
15,
22,
28,
33,
40]. One study found that a genetic polymorphism of the serotonin transporter (5-HTT (5-hydroxy tryptamine)] gene) may have led to higher rates of PTSD post 9/11 [
45]. Personality characteristics associated with PTSD include negative affectivity, detachment and psychoticism, as well as less perceived self-efficacy [
51,
54]. In first responders, having only basic life-saving training versus more intermediate or advanced training, was found to be a risk factor for PTSD [
31]. During the terrorist attack, the main predictors for developing PTSD are level of exposure [
48,
73], including experiencing high perceived threat and having witnessed a life-threatening injury [
12,
36]. Higher perceived threat is a predictor for developing PTSD even in individuals who did not directly witness the attacks [
36]. Following the terrorist attack, having low social supports, comorbid depression, anxiety and alcohol use have been shown to be risk factors for developing PTSD [
8,
13]. Suffering a physical injury secondary to the terrorist attack, regardless of the severity of the injury, is one of the biggest predictors of developing severe PTSD [
22].
Regarding first responders, having had only basic life-saving training, as opposed to intermediate or advanced training, as well as having to intervene on unsecured crime scenes, likely leading to higher fear of death, were found to be risk factors for developing PTSD [
31,
44]. Certain studies also commented on risk factors associated with increased severity of PTSD. These include low social integration into the community, higher level of exposure to the attack, job loss following the event, marital status, unmet mental health needs, low education and socio-economic status, being a female and being of Hispanic descent [
27,
42,
52,
60]. In regard to symptomatology and comorbidities, risk factors for more severe PTSD include having severe hyperarousal symptoms, experiencing bereavement, being injured by the attack, having a history of PTSD, depression or anxiety pre-attack, having other medical conditions diagnosed post-attack, higher levels of exposure to the attack and a lifetime trauma burden, especially post attack [
27,
42,
60]. Finally, from a temperament perspective, using coping strategies such as substance use and avoidance, as well as callousness and perceptual dysregulation personality traits, can worsen the trajectory of the illness [
51,
60].
1.2. Protective Factors
When individuals and communities are exposed to terrorism, certain factors have been shown to protect against the development of mental illness. With regard to other forms of trauma, the general understanding is that adaptive coping strategies, greater social support and a sense of purpose are linked to lower PTSD symptoms [
84]. These have similarly been shown to be protective factors in the context of terrorism exposure [
60]. For first-line workers, feeling well prepared prior to the event, higher levels of training, feeling supported by leadership, lower role conflict, higher role clarity and predictability have shown to lead to lower rates of PTSD and less psychological distress [
56,
59,
60]. More optimistic personality styles, benign styles of humour, perceived self-efficacy and the belief of having a life purpose all were traits that were associated with lower rates of psychological distress and post-traumatic symptomatology [
54,
55,
57,
60]. Individuals who employ problem solving and cognitive restructuring coping strategies were associated with fewer post-traumatic reactions and active coping skills distinguished between improving and chronic trajectories [
60,
62]. Finally, less severe emotional numbing symptoms was associated with higher rates of symptom recovery [
27].
1.3. Symptom Clusters and Course of Illnesses
PTSD is often a chronic and highly disabling illness with an 18–50% recovery rate within the first 3–7 years. The four symptom clusters of PTSD include continuously reliving the traumatic event, persistent avoidance of stimuli related to the event, symptoms of emotional numbing and increased arousal response [
84,
85]. In first-line workers who intervened during terrorist attacks, especially volunteers, studies have shown that rates of PTSD continue to increase until a peak at 5–6 years post event. With regard to PTSD related to terrorism, even 6–7 years after the attack, 15–26% of direct victims continue to report PTSD symptoms [
74]. Compared to other sources of PTSD, terrorism leads to a longer duration of illness (202 versus 92 months), with non-traditional workers showing the highest rates of chronic symptoms [
67,
75]. In one study, there was no statistically significant difference in the severity of symptoms between PTSD related to terrorism versus other forms of PTSD; however, higher avoidance symptoms were found, which is generally a severity marker [
67]. However, one study out of Italy showed higher severity scores on the CAPS scale in terrorism than other forms of trauma [
75]. When examining symptoms related to reliving the trauma, auditory reminders were the most frequently encountered and the most distressing [
68,
69]. One study found that the most central symptom seen in PTSD in the context of terrorism is feeling emotionally numb [
66].