A sizable proportion (29.6%) of the study population deployed in support of the Afghanistan mission used Canadian Forces mental health services during the follow-up period. Of these, an important minority (13.5%) had a mental disorder perceived by a clinician to be related to the deployment. The most common of the disorders was PTSD. The overall probability of an Afghanistan-related mental disorder started to plateau after 6 or more years of follow-up, with a cumulative incidence that approached 20% by the end of the follow-up period. The probability was highest among personnel deployed to Kandahar.
Deployment to higher-threat locations, service in the Canadian Army and lower rank were independent risk factors associated with an Afghanistan-related mental disorder. In contrast, no independent association was seen with sex, Reserve Forces status, multiple deployments or deployment length. However, power to detect small differences was limited.
Because of methodologic differences, we were unable to directly compare our results with more widely available prevalence data from surveys. For example, in a 2002 survey, the 12-month prevalence of PTSD in the Regular Forces was 2.8 and the lifetime prevalence 7.3%.24,25
The structure of that survey prevented attribution of individual cases of PTSD or other mental disorders to a deployment, and those data predate both the Afghanistan conflict and the renewal of the Canadian Forces mental health services.
Data from postdeployment screenings showed that about 5% of personnel who returned from Afghanistan-related deployments since late 2005 had symptoms of PTSD or depression, or both, 6 months after their return; in most cases, the disorders were judged to be related to the most recent deployment.15
Anonymous survey data collected during 2008/09 from recently deployed personnel showed that about 8% screened positive for symptoms of PTSD with the use of a 4-item screening tool.26
However, not all of those who screened positive at the cut-off used would have received a diagnosis of PTSD,27
and the survey’s anonymous nature may have influenced results.28
The extensive survey data reported by other countries raise the same and other comparability issues.29
Data from historical conflicts raise even larger issues,6
including changes in the conceptualization of trauma-related disorders.30
Studies that have used administrative data on mental health care encounters are more comparable: Hoge and colleagues2
found that 9%–12% of US Army personnel returning from Iraq had a mental disorder diagnosed within about a year after their return; the proportion related to the most recent deployment was unknown.
Although methodologic differences preclude direct comparisons, the findings from current and past conflicts do cohere.29
For example, military personnel exposed to heavy combat have higher rates of PTSD or other mental disorders than personnel in lower-threat locations, prevalence estimates of symptoms are higher than those of clinical diagnoses, and less specific screening instruments result in higher rates of symptoms.
Others have noted the high proportion of personnel who sought care after returning from deployment31
and the predominance of PTSD and depression as the primary service-related mental disorders.32
Others have also noted the higher rates of mental disorders among Army personnel and those of lower rank.33
Although concerns have been raised about an increased risk of deployment-related mental health problems among women,34
personnel with multiple deployments36
and those with more prolonged deployments,37
we found no such associations. Our finding of a strong association with deployment location mirrors data on the health effects of different deployments: for example, no association between deployment and mental disorders was seen for US peacekeeping deployments to the Middle East, Bosnia or Kosovo in the 1990s,33
whereas a strong association was seen for the current conflicts in Southwest Asia.3,38
Much of the association between an Afghanistan deployment–related mental disorder and lower rank, Army service and deployment location was likely mediated by combat exposure, which is known to be a strong, consistent and independent predictor of postdeployment mental disorders.6
However, there was a meaningful incidence of mental disorders related to the Afghanistan mission among personnel who had not had any combat exposure (e.g., those stationed in the United Arab Emirates).
Strengths and limitations
The strengths of this study include its reflection of the full range of personnel deployed in support of the Afghanistan mission; the prolonged follow-up period; the use of rigorous diagnostic assessments by clinicians experienced in the assessment of trauma-related disorders; the ability to attribute diagnoses directly to the Afghanistan-related deployment; and the use of survival analysis as the analytical approach.
The most important limitation of this research is that it captured only diagnoses made by the Canadian Forces mental health services during the follow-up period. We could not identify personnel who had mental disorders that resolved without care; those who were seen only in primary care or outside of the Canadian Forces; those who had not yet fallen ill39
or had not yet sought care; and those who sought care only after release from the Canadian Forces.
Errors in diagnosis were possible. However, the lengthy, standardized and collaborative nature of the assessment and the extensive experience of Canadian Forces clinicians with service-related mental disorders argue against that as a major source of bias. The potential for errors on the part of the clinician in attributing diagnoses to Afghanistan-related deployments are harder to dismiss. The Canadian Forces does not have a standardized approach to determine the association with deployment. In addition, clinicians may have erred on the side of attributing the diagnosis to the deployment out of a desire to assist the patient in qualifying for later benefits. These same limitations are inherent in all research relying on clinical data. Other mechanisms (e.g., population-based surveys) will be required to better understand the impact of the Afghanistan mission and to situate it in the context of mental disorders writ large in the entire Canadian Forces.40
Finally, our failure to assess physical health problems in the cohort makes it impossible to place mental health into a larger health context.
An important minority of Canadian Forces personnel received a diagnosis of a mental disorder related to deployment in support of the Afghanistan mission. Deployment to higher-threat locations, service in the Canadian Army and lower rank were independent risk factors. This study provided a precise and methodologically rigorous estimate of the impact of the Afghanistan mission on the risk of mental disorders during continued military service. These findings will have implications in terms of service delivery and veterans’ benefits. Future research with this cohort will explore the process and outcomes of the mental health care delivered to personnel with mental disorders related to the Afghanistan mission.