A primary study for CFS requires that it be diagnosed by a health professional. A secondary study is one in which a CFS-like condition has been documented and a comparison is made between deployed and nondeployed veteran populations. Self-reports of CFS and self-reports of a physician diagnosis of CFS were included in the secondary studies. The primary studies of CFS are summarized in Table 6-6.
The only primary study identified by the committee is that of Eisen et al. (2005), a cross-sectional prevalence study of 12 health measures in 1061 Gulf War-deployed and 1128 nondeployed veterans conducted in 2001 as part of the National Health Survey of Gulf War Era Veterans and Their Families. All randomly selected study participants had participated in the 1995 phase of the survey by completing a mail or telephone questionnaire about their health. CFS was diagnosed by clinical examination on the basis of the International Chronic Fatigue Syndrome Study Group case definition (Fukuda et al. 1994) by VA clinicians who were blind to the deployment status of the veterans. Veterans with psychiatric disorders were excluded from the sample. Eisen et al. (2005) found that only three of the 38 deployed veterans who self-reported CFS met the criteria on examination and only two of the eight nondeployed veterans who self-reported CFS received this diagnosis, so the authors concluded that self-reports of CFS in both deployed and nondeployed veterans are unreliable. Clinically diagnosed CFS, however, had the largest OR of the 12 medical illnesses or symptoms addressed. CFS was more prevalent in deployed veterans (1.6%) than in nondeployed veterans (0.1%) giving an OR of 40.6 (95% CI 10.2-161.15, p < 0.001) after adjustment for age, sex, race, cigarette-smoking, duty type, service branch, and rank. The strengths of this large study are its population-based design, stratified sampling method, analysis of participation bias, comprehensive examination, and use of computer-based algorithms by researchers who were blinded to deployment status. One limitation is the low response rates: 53% of the eligible deployed veterans and 39% of the eligible nondeployed veterans.
The committee identified six secondary studies that explored the relationship between deployment to a war zone and CFS. In all six, a diagnosis of CFS was self-reported, CFS was determined on the basis of self-reports of symptoms similar to those of CFS, or the presence of CFS was based on criteria other than those of CDC. Gray et al. (2002) found an OR of 7.60 (95% CI 4.76-12.13) for self-reports of physician-diagnosed CFS in Gulf War-deployed Seabees vs nondeployed Seabees; the OR was adjusted for age, sex, active-duty or reserve status, race or ethnicity, current smoking, and current alcohol-drinking. The prevalence of CFS was 5.17% in the Gulf War-deployed Seabees (n = 3831) who reported such a diagnosis, 0.79% in Seabees deployed elsewhere (n = 4933), and 0.68% in nondeployed Seabees (n = 3104).
In a survey of UK military personnel deployed to the Gulf War or to Bosnia or on active duty but not deployed, Reid et al. (2001) found that the prevalence of CFS was not statistically different between the Gulf War-deployed and nondeployed troops (2.1% vs 1.8%), but both groups had a greater prevalence of CFS than did the group deployed to Bosnia (0.7%). CFS was determined by the researchers on the basis of responses to a fatigue questionnaire combined with the SF-36 questionnaire for functional disability to meet the CDC criteria for CFS. The OR for CFS in the gulf vs Bosnia groups was 2.3 (95% CI 1.2-4.3) and in the gulf vs era veterans 1.2