The September 11, 2001 (9/11) Al Qaeda terrorist attack was the deadliest terrorist attack in American history (Berninger et al., 2010). At the World Trade Center (WTC) itself, 2753 people perished; this number includes 403 first responders: 343 Fire Department of New York (FDNY) personnel along with 60 New York Police Department (NYPD) and Port Authority Police Department (PAPD) members (Farfel et al., 2008). The ultimate collapse of multiple massive buildings released a toxic cloud containing the pulverized remains of the buildings, dust, and byproducts of burning jet fuel that thousands of people inhaled (Farfel et al., 2008). These factors combined to give the 9/11 attacks a traumatic salience that was, for many, both psychological and physical.

In the two decades since 9/11, there has been extensive research on the long-term mental and physical health of all those exposed to 9/11-related trauma. The experiences of individual responders and civilians on that day varied greatly depending on location, time of arrival to the WTC, and degree of exposure to the disaster (Mauer et al., 2007; Lowell et al., 2018; Niles et al., 2013). Given that the group of responders who arrived at the WTC on 9/11 itself – a group we will call the “9/11 early responders” – moved in the direction of greatest danger under life-threatening conditions in a rapidly evolving disaster scenario, it is reasonable to hypothesize that this group may have higher longitudinal rates of mental and physical illness relative to other 9/11-exposed populations. It can be challenging to evaluate this hypothesis given significant heterogeneity in how 9/11-related articles gather and report data: information on 9/11 early responders is often mixed in with information from groups with much less acute exposure to the disaster for whom the severity of the psychological and physical threat were quite different (Smith et al., 2019). Articles drawing from FDNY data sets, which stratify data on responder health by responder arrival time to the WTC, have the option to comment on differential 9/11 exposure intensities and resulting relative rates of illness, but unfortunately not all do. Other articles drawing from non-FDNY data do not have access to stratified data and usually group survivors together in large analyses without comment on time of arrival to the WTC. Nevertheless despite these considerations, fortunately there is ultimately enough evidence in the literature to comfortably confirm that general rates of mental and physical illness are higher among 9/11 early responders relative to other 9/11-exposed populations; this conclusion does not necessarily extend to all individual conditions (Smith et al., 2019; Lowell et al., 2018).

More recently, an emerging body of literature has begun identifying associations and/or mediations between mental and physical illness in the general 9/11-affected population (Koraishy et al., 2021; Jordan et al., 2013; Litcher-Kelly et al., 2014). The finding of associated mental and physical health detriment in this population corresponds with separate research in individuals exposed to similarly mentally and physically salient traumas, such as veterans of the Iraq and Vietnam wars (Hoge et al., 2007; Schnurr, Jankowski 1999). Other research renders these associations quite relevant for healthcare providers by highlighting the importance of treating mental and physical illness in tandem for trauma-exposed individuals, particularly when associations have been defined between the two (Duan-Porter et al., 2021; Angleman et al., 2022; Zatzick et al., 2001). It is important to note, however, that whereas commentary on prevalence of mental and physical illness specifically among 9/11 early responders is to be found to some extent in the literature as above, we were unable to locate a single article in our preliminary search which aimed to investigate associations between mental and physical illness in this population.

We feel that the lack of formal characterization of associations between mental and physical illness specifically in the uniquely traumatized 9/11 early responder population itself is a significant gap in the 9/11 literature with important implications (Smith et al., 2019; Lowell et al., 2018). All responders suffering from mental and physical illness as a result of their contribution to the rescue and recovery effort on and after 9/11 deserve to be recognized and appreciated; at the same time, there is broad evidence in the literature demonstrating that as severity and/or chronicity of mental and/or physical illness increases, adherence to psychiatric and medical care decreases, and ultimate health outcomes worsen (Peckham et al., 2021; Khalifeh et al., 2023; DiMatteo et al., 2007; Spoont et al., 2005; Burstein 1986). This means that mental and physical illness in 9/11 early responders may associate with one another differently than they do in larger groups of 9/11-impacted individuals that are, together, at lower risk of poor long term health outcomes. Given this, and given that mental and physical illness have the potential to significantly worsen each other bidirectionally, we feel that it is critically important to characterize associations between the two specifically in a population at particularly elevated risk of poor long term health outcomes (Solmi et al., 2023; Docherty et al., 2016).

The aim of this systematic review is to serve as a first step towards filling the gap in the literature described above by beginning to formally characterize potential relationships between mental and physical illness profiles among 9/11 early responders. As a first step, we elected to explore what is known about the interplay between PTSD and lower respiratory symptoms (LRS) in this population. We chose to focus on these particular syndromes for two reasons. First, they represent, respectively, an important mental illness and an important constellation of physical symptoms, both of which are among the most salient and prevalent conditions in the population of interest: roughly 9000 FDNY personnel and an unclear number of NYPD and PAPD members (Smith et al., 2019; Lowell et al., 2018). Second, there is a hypothesized bidirectional interaction between PTSD and LRS in the literature which makes exploration of associations between the two in this population particularly relevant (Wyka et al., 2020). PTSD is thought to worsen LRS by exacerbating pulmonary inflammation through chronically increased sympathetic activity; LRS, in turn, may worsen PTSD by serving as a constant reminder of the original trauma and/or by impairing functioning to the point where engaging with PTSD treatment is difficult (Wyka et al., 2020). We discuss how the information elicited by this review can begin to help optimize treatment specifically for 9/11 early responders and can hopefully inspire further research into mental and physical health in this important group. We also comment on implications of this research for survivors of other serious non-9/11 trauma, including potential future disasters.