Because ASD is a new diagnosis, there are few investigations available on its prevalence or natural history. Future research will examine to what extent this diagnosis predicts the later onset of Post-Traumatic Stress Disorder and other psychiatric conditions. Although only a minority of survivors of most disasters develop diagnosable cases of PTSD, some symptoms may be abundant or even universal. The natural history of PTSD is that symptoms often begin within hours, and usually within a few days, of the traumatic event. PTSD symptoms typically begin to fade within weeks of the event, although this can vary considerably.
Many studies report that roughly half of the cases in the general population resolve by six months.
Chronic PTSD with symptoms which can persist for many years, however, has also been described, including one-third of the cases persisting for at least three years. Chronicity has been predicted by the presence of pre-existing psychiatric disorders, neuroticism, a history of early separation from parents in childhood, and family history of anxiety or antisocial behavior, as well as litigation. Research indicates that other psychiatric disorders often accompany PTSD in disaster survivors. The most prevalent co-existing disorders appear to be major depression and anxiety disorders. Given the well documented potential for improvement with treatment, these disorders should not be overlooked in evaluation of disaster survivors for post-traumatic symptoms.