What’s New in Psychology

A 20-Year Study of World Trade Center Disaster Helps Shape New Insights on PTSD    

Jim Windell

            Post-traumatic stress disorder (PTSD) can develop after exposure to a traumatic event. Although about half of all U.S. adults will experience at least one traumatic event in their lives,  most do not develop PTSD. However, those who do – and that number is an estimated 3.6 % of adults – may have persistent, frightening thoughts and memories of the event(s), experience sleep problems, feel detached or numb, or may be easily startled.

            For many people who have experienced PTSD the symptoms dissipate over time, but for others the effects may go on, perhaps for years. I remember a man I met who was diagnosed with PTSD as a result of various horrific events during World War II. When I met him, some 40 years after WWII, he was still showing symptoms of PTSD. However, the fact is that we don’t know much about the long-term trajectory of PTSD. The main reason for this is the dearth of long-term studies of the disorder.

            But a new study published online recently in Nature Mental Health may shed more light on what happens to people with PTSD, the rates of recovery and potential new insights for treatment.

             In the study led by Frank D. Mann, PhD, a senior research scientist at Stony Brook University Renaissance School of Medicine, Stony Brook, New York, researchers analyzed data from the World Trade Center Health Program (WTCHP), which is administered by the CDC’s National Institute for Occupational Safety and Health (NIOSH).

           Participation in the WTCHP is voluntary, but those who enroll receive free assessments, monitoring, and treatment, including psychiatric and behavioral healthcare. It is the longest and most detailed analysis of PTSD and includes 81,298 observations from 12,822 WTC responders. The participants entered the WTCHP at different timepoints and were assessed annually. Not every enrollee was assessed every year, but the sheer number of participants and observations “just provides much greater density of data over that 20-year course than any previous study,” says Mann.

           Responders were assessed regularly using the PTSD Checklist for a Specific Stressor, a standardized tool that measures symptom severity on an 85-point scale. On average, each participant completed 6.3 assessments over the course of the study.

           A score of ≥ 44 was considered indicative of clinically elevated PTSD symptoms. Between 2002 and 2022, the crude prevalence of elevated symptoms ranged from 8% to 15%. At the same time, 16% to 34% of responders each year reported little to no symptoms, scoring at or near the minimum on the scale, thus, the researchers found that symptom trajectories varied widely. Nearly as many participants experienced worsening symptoms as those who improved. As a result, the overall population average remained relatively flat over the 20-year period.

           Among responders who met the threshold for PTSD, the median time to symptom improvement was 8.9 years — and by year 20, about 76% had shown improvement.

           Mann said the study not only reinforced existing knowledge about PTSD in responders but also uncovered new insights. Most notably, it showed that PTSD symptoms tended to peak around a decade after 9/11 — significantly later than delayed-onset patterns reported in previous trauma studies. He also noted a surprising outcome — the top 10% of responders who experienced worsening symptoms over the long term accounted for the majority of mental health costs. These individuals, Mann said, represent a critical gap in care, with current interventions proving largely ineffective for them.

           Mann suggested that ongoing trauma exposure — especially for responders still in high-risk jobs — and potential genetic susceptibility may contribute to late-emerging or persistent symptoms. “These individuals are an urgent priority for health systems, as available resources have not been effective for them,” Mann and the other authors wrote in the report.

           Mann and his colleagues also found that occupation offered the strongest protection against developing PTSD. Police officers and firefighters benefit from training designed to help them cope with trauma, and repeated exposure may build a degree of resilience. In contrast, responders without such training — like construction workers — faced a 50% to 55% higher risk of developing PTSD symptoms. Mann emphasized that occupational status was a more powerful predictor of PTSD risk than the severity of the traumatic exposures themselves.

           Commenting on the study, James West, MD, chair of the American Psychiatric Association’s Committee on the Psychiatric Dimensions of Disaster, described the finding that 10% of responders continued to experience symptoms two decades after exposure as “sobering.” However, he emphasized that it aligns with observations in the disaster recovery community, where the psychological impact “goes way beyond what most people see as the immediate aftermath and recovery.” West stressed the urgent need to develop effective treatments that enable those affected to live fuller, less impaired lives.

           “We still need to be finding the effective treatments that can help these people live fuller lives without impairment from their trauma symptoms,” said West.

           To read the original study, find it with this reference:

Mann, F. D., Waszczuk, M. A., Clouston, S. A., Feltman, S., Ruggero, C. J., Marx, B. P., ... & Kotov, R. (2025). A 20-year longitudinal cohort study of post-traumatic stress disorder in World Trade Center responders. Nature Mental Health, 1-14.