The challenges and benefits of conducting linked epidemiological and neurobiological health surveillance into the impacts of military deployment in Australia

Background

There are very few areas of mental health that evoke public interest such as the impact of deployment on the mental health of military personnel. While there has been long-standing acceptance in the public mind about the negative impact of deployment, the hypothesis of the substantial causal role of combat exposure has often been resisted by medical practitioners. As a consequence, independent research has played a critical role attempting to clarify the facts in this, at times, vexed debate. This editorial highlights the context and challenges faced by current health surveillance research of Australian Defence Force (ADF) Personnel and the potential contributions this body of work can make more generally to mental health.

The current deployments to Iraq and Afghanistan have lasted three times longer than the duration of the World War 1 and 2, highlighting the importance of documenting the cost of repeated deployments. As these conflicts are likely to continue, there is an ongoing need to investigate the impact of the traumatic and toxic environmental exposures on the mental and physical health of the deployed personnel. In past conflicts, the consequence of environmental exposures has been a particular pre-occupation of veterans as a cause of post-deployment ill health, in particular Agent Orange on Vietnam veterans and multiple vaccinations on the health of Gulf War veterans. The conduct of credible, independent research has been instrumental in addressing these ongoing controversies. Following the Vietnam War, when posttraumatic stress disorder (PTSD) was first accepted in 1980, there was a significant reluctance within the US Department of Veterans’ Affairs to accept its validity. It was only the independently mandated research by the US Congress in 1983, which substantially silenced the critics and set the benchmark for documenting the long-term effects of combat exposure (Marmar et al., 2015). This cohort was recently followed up 40 years after the end of the Vietnam War further highlighting the increasing psychological morbidity and associated mortality of high levels of combat exposure with increasing age.

The need for longitudinal health surveillance

A central methodological challenge to the conduct of valid research is being able to capture the exposures and health outcomes of military personnel in close temporal proximity to their deployment. This is essential in order to minimise the risks of recall bias and enable the development of a systematic plan for long-term follow-up. This requires a substantial Government commitment and a capacity for institutional memory to sustain such research programs. An example of such a program in the United States is the Millennium Cohort Study, which plans to follow 100,000 US personnel over a 30-year period (Smith et al., 2011). The Deployment Health Surveillance Program in Australia followed a commitment by Minister Scott in 1999 and has collected Bougainville, Solomon Islands and East Timor as well as the Middle East Area of Operations deployments to Afghanistan and Iraq (e.g. Davy et al., 2012). Critically, these studies have been conducted by research teams, which are independent from the Departments of Veterans Affairs and Defence (ADF), providing veterans assurances about the impartiality of the findings.

The duration of the current conflicts in the Middle East has provided a unique research opportunity to extend deployment health surveillance studies beyond the standard psychological, behavioural and social after-effects to investigate the neurobiology underpinning these outcomes (Yehuda et al., 2013). There are now a series of studies, for example, that have examined ADF personnel prior to and following deployment to the Middle East which have highlighted dysregulation in a range of biological systems, including inflammatory mediators, neural circuitry and glucocorticoid function (McFarlane et al., 2017). The findings of this research support the notion of PTSD being a systemic disorder rather than a simple state of psychological distress (McFarlane et al., 2017).

These studies have taken on greater importance in light of the recent Mental Health Commission Report and the recently released report of the Joint Standing Committee for Defence, Foreign Affairs and Trade of the Senate into veterans’ suicide and the adequacy of mental health care provided to the veterans’ community and ADF personnel. These two reports highlight the critical need to examine both current and transitioned ADF members, as it is in these individuals that the significant morbidity arising from deployment exposures is likely to be most apparent. Although the recruitment process selects healthy personnel, the ADF has similar mental health to the general population of Australia due to the stresses of military service. However, transitioned personnel are likely to have significantly worse mental health because those who are injured or have a psychiatric disorder are more likely to be medically discharged. The release of these findings is imminent in a major report to government.

Outcomes

Studies of veterans have repeatedly demonstrated the co-occurrence of somatic symptoms and mental health symptoms, particularly following events involving actual and witnessed life-threat, loss and human suffering (Smith et al., 2011). These psychological exposures frequently occur in environments where there are a number of chemical and/or biological hazards. The repeated question, in the mind of veterans, is the extent to which the root symptoms and emerging disease are caused by toxic agents, rather than the psychological stresses and strains. The most recent controversy is the extent to which exposure to blast injury, particularly as a consequence of exposure to an improvised explosive device, accounts for symptoms that are otherwise and typically attributed to PTSD (Davy et al., 2012). The implicit claim is that treating PTSD only ignores the underlying aetiology of the associated symptoms such as sleep disturbance, cognitive difficulties and irritability. The challenge, however, is that these symptoms equally occur in PTSD. What this argument ignores is the now extensive evidence about the underlying neuropathology of PTSD at a cellular, functional and morphological level (Yehuda et al., 2013).

The conceptual challenge of understanding how there can be such a significant delay between combat exposure and the emergence of morbidity has been one of the greatest impediments to understanding and accepting the costs of going to war. Longitudinal cohort studies have demonstrated unequivocally that rates of disorder progressively increase with time. The focus of military psychiatry up until the end of the Vietnam War on the management of acute combat stress reactions has biased attention to the acute impacts of combat exposure rather than the long-term consequences. Previously there has been little anticipation of the emergence of delayed-onset PTSD (McFarlane et al., 2017). However, a central finding from longitudinal surveillance studies is that a substantial number of PTSD cases do not emerge until years after the battlefield exposures (Marmar et al., 2015). These epidemiological observations are underpinned by the demonstrated neurobiological dysregulation caused by combat exposure that is a risk factor for later sensitisation and is reinforced by increasing reactivity to threat and environmental triggers. Furthermore, these surveillance studies demonstrate that PTSD is only one disorder caused by combat with major depressive disorder, obsessive-compulsive disorder and panic attacks also a common sequelae.

Policy implications and future directions

Scientific research into the relationship between physical and mental health and deployment informs a series of domains. First, the Australian Federal Government created a statutory body, the Repatriation Medical Authority (RMA), to simplify the determination process of veterans’ entitlements for health conditions caused by deployment. Rather than having experts giving conflicting opinions based on selective review of the scientific literature, the RMA develops statements of principles informed by a systematic view of peer-reviewed literature on military populations. Studies of deployment therefore provide a valid evidence base to inform pension entitlements for the veterans’ community. This necessitates adequate funding for not only the conduct of these studies but also for the publication of the data collected from these studies, in order to ensure the knowledge is utilised by the RMA.

The second area of importance is to better understand the underlying mechanisms and causal factors in deployment-related conditions such as PTSD. The US Departments of Defence and Veterans Affairs have recognised this imperative, focussing their attention on biomarker research as a means of developing more effective treatments for PTSD (Yehuda et al., 2013). Such research has a broader social relevance, as PTSD, particularly in Australia carries the substantial burden of morbidity in the civilians, partly due to the limited effectiveness of existing evidence base treatments such as psychotherapy and drug interventions for a significant proportion of veterans. Currently, there is a marked lack of new and emerging treatments being trialled for the treatment of PTSD. Given the fact that PTSD is the most common disorder using International Classification of Diseases, 10th Edition (ICD-10) criteria in the Australian community and a major concern in veterans, it is somewhat paradoxical that no individual pharmaceutical treatment has been developed primarily for the treatment of this condition. The neurobiological research of deployed military personnel using prospective designs may lead to potential targets for drug treatment.

Studies of deployment-related mental health can also inform prevention. There is an increasing body of evidence about the role of cumulative trauma in the onset of PTSD (McFarlane et al., 2017). This is in direct contrast to the emphasis placed in the diagnostic criteria on a single event type leading to the emergence of the disorder. Studies of deployed military personnel highlight the importance of cumulative trauma exposure in combat and warlike environments, but the impact of this exposure still needs to be considered against the background of the cumulative burden of lifetime trauma exposure (Smith et al., 2011). Examples include military training accidents and motor vehicle accidents which are not uncommon during military service and contribute to the mental health burden in military personnel.

Individuals with emerging symptomatic distress following repeated trauma exposure are those at particular risk following further exposure (McFarlane et al., 2017). This emphasises that subsyndromal disorder is not a benign condition but rather a significant predictor of emerging disorder. The use of a staging approach to characterise the emerging symptoms of PTSD is an approach that can assist in the development and better targeting of interventions in order to ensure that treatment is effective at each of the different points in the progression of the disorder. Identifying early shifts in neurobiological dysregulation is likely to result in more effective targets being identified which will consequently lead to better treatment outcomes.

There are few areas of medical research where stakeholders have the same degree of commitment and interest in research excellence as the researchers themselves. The veterans’ community demand impartial research of high quality to determine the costs of going to war. Government, on the other hand, has an obligation both to provide effective care and to limit liability for claims based on spurious causal hypotheses. The broader community has a significant investment in acknowledging and honouring those who serve the nation. To meet these competing obligations, it is critical that there is an excellent standard of research governance and planning. This requires bureaucracies to have a stable cohort of personnel with the appropriate skills and knowledge to advocate for and oversight site large-scale longitudinal research programs. Unfortunately, institutional memory about why particular research programs were commenced is vulnerable to decay and this requires advocacy, oversight and long-term planning by individuals with the necessary technical knowledge.

The $30 million that has been spent to date on the Australian Deployment Health Surveillance Program is only the foundation on which the health outcomes of contemporary veterans will be researched. Forward planning, thorough data analysis and international collaboration are central to the future success of this major investment. Adequate funding is necessary to sustain a core research team who understand the structure of the research to date and its potential to answer emerging research questions. The veterans’ community needs to be actively involved and engaged in the oversight of the research program and the promulgation of research findings so their concerns and needs are met as well as knowledge is gained in the broader scientific enterprise.