In this study of retired WTC-exposed firefighters, we found high rates of PTSD and depression risk and high comorbidity. While we cannot rule out potential confounding factors from other traumatic events, 80% of those with elevated PTSD risk reported the WTC collapse was the most emotionally terrible event of their lifetime. Other studies have shown WTC exposure to be associated with increased rates of depression or PTSD,22–26
but this is the first report of such high prevalence rates occurring comorbidly in 9/11 first responders. In fact, four to six years after 9/11, these rates were as high as those reported in Vietnam veterans,27
clearly supporting continued monitoring and treatment for trauma-induced mental health consequences in this population.
Screening instruments validated separately for depression and PTSD share some similar symptom questions and, therefore, it has been suggested that the presence of one condition raises the risk for the other due to symptom question overlap rather than true comorbidity between these conditions.9
Yet, the investigator is faced with the fact that these validated questionnaires are widely used, cannot easily be changed, and that distinct differences in overall symptom profile are widely acknowledged and used by clinicians to identify each disease separately or comorbidly. Shared vulnerabilities were noticed in earlier WTC studies2,7,12,13
and in other non-WTC studies,28
but those analyses did not evaluate risk factors that might have mediated comorbidity in an effort to identify unique correlates for each condition.
To further understand the relationship between 9/11 trauma and mental health risk in retired FDNY firefighters, we analyzed correlations between selected characteristics and elevated depression and PTSD risk. As shown in previous studies,12,13
multivariable logistic regression models not controlling for comorbidity () identified WTC exposure, retirement with a disability pension, and alcohol use disorder as associated with current elevated depression and PTSD risk. We then explored mediation analyses using these variables as characteristics of interest using two methods: (1
) a series of logistic regressions controlling for the variable suspected of having a confounder role and (2
) logistic regressions on the population stratified by mental health status.
Regression analyses in this study demonstrated increased elevated depression and PTSD risk with earlier WTC arrival time, but elevated PTSD risk mediated the relationship between elevated depression risk and WTC-exposure group when either of the aforementioned methods was applied. Although we did not find a dose-response gradient between WTC exposure and elevated depression risk, we noted that the prevalence of elevated depression risk (22.7%) was much higher in WTC-exposed retired FDNY firefighters than in other WTC-exposed populations (range: 9.7%–16.1%),2,22,29
a sample of older white Brooklyn residents (10%),30
and in the 12-month prevalence of a national sample of men (4%) and men ≥60 years of age (2.1%).31
Alcohol abuse has been previously identified as associated with increased risk of depression.32
The association between alcohol abuse and PTSD, however, is not as well understood, with studies presenting different interpretations.33,34
Our study found alcohol abuse to be associated with both elevated depression and PTSD risk. The association between alcohol abuse and elevated PTSD risk, however, was no longer statistically significant after adjusting for elevated depression risk. This finding is consistent with the hypothesis that the association between alcohol use and elevated PTSD risk was mediated by elevated depression risk.
Elevated risk for PTSD and depression was also associated with disability retirement for physical injuries or illnesses in multivariable models, supporting previous research finding associations among PTSD, depression, and a range of physical ailments.35
With a large proportion of our sample having retired with disability, this may also explain, in part, the higher rates of elevated depression risk when compared with national samples, with presumably far lower rates of disability. Extensive examination of the effect of disability retirement was beyond the scope of this study, but warrants future investigation.
Consistent with Blanchard et al., our models suggest that elevated depression and PTSD risk may be separate constructs.10
After controlling for comorbidity in the current study, we identified unique correlates for each condition, which support the premise that depression and PTSD are independent responses to trauma.
Our findings add to the growing understanding of traumatic events, but our study had several limitations. First, we did not specifically account for exposure to traumatic events unrelated to 9/11, occurring before 9/11, or occurring between 9/11 and the date of the health evaluation. This factor was partially addressed by modifying the PCL so that subject answers to questions were clearly in the context of 9/11. We also examined each member's most stressful lifetime event (with 78% of the cohort and 80% of those with elevated PTSD risk identifying the WTC collapse). Despite these efforts, it is possible that other lifetime events could impact PTSD development, regardless of whether these events were identified as the “most stressful.”
A second limitation was the cross-sectional study design, which prevented drawing conclusions about the direction of potential mediation and also prevented differentiation between chronic and delayed-onset morbidity.36
Third, screening questionnaires are not clinical diagnoses, which is why we used the qualifier “elevated risk” to describe depression and PTSD prevalence based on our questionnaire results. Previous studies, however, have shown the CES-D and the PCL to have good correspondence with clinical diagnoses.37–43
Finally, the generalizability of these results is limited to retired WTC-exposed male firefighters until further studies can be performed on other trauma-exposed populations.