fatigue, 4.9% of deployed and 1.2% of nondeployed veterans (OR 4.2, 95% CI 3.3-5.5) met the case definition. The investigators found that CFS was not related to the severity of combat stressors. The latter was assessed according to responses to questions on wearing chemical protective gear or hearing chemical alarms, being involved in direct combat duty, or witnessing any deaths. The study was limited by its reliance on solely self-reported symptoms without a physical or laboratory examination and on self-reported physician-diagnosed conditions. Those shortcomings resulted in a higher rate of CFS-like illness than was observed when the same cohorts were sampled and underwent more rigorous medical evaluations as in Eisen et al. (2005).
Proctor and colleagues (2001) conducted in-person interviews of 180 Army veterans selected from the larger Fort Devens cohort to determine the prevalence of CFS. The deployed veterans were compared with 46 members of an air ambulance company deployed to Germany during the Gulf War. The prevalence was determined only according to the symptom criteria specified by the CDC case definition (Fukuda et al. 1994). With that approach, the rate was higher in the Gulf-deployed than the Germany-deployed group (7.5% vs 0%, p = 0.02). When additional information from self-reported medical or psychiatric conditions (such as substance abuse and bipolar disorder) and clinical psychiatric interviews was considered, the prevalence in Gulf veterans decreased to 2%, which was no longer statistically significant. The study demonstrated the importance of performing psychiatric assessments, but it was limited by the relatively small sample and the lack of medical or laboratory evaluations.
Canada deployed more than 3,000 sea, land, and air troops to the gulf region; they participated in a naval blockade and were responsible for one-fourth of enemy interceptions in the gulf. A survey of the entire Canadian Gulf War forces found that deployed veterans were at least 5 times as likely as nondeployed veterans to report symptoms of CFS (OR 5.27, 95% CI 3.95-7.03) (Goss Gilroy Inc. 1998). Veterans were not interviewed or examined, and all data were obtained from self-reports. The CFS-like illness was based on responses to questions derived from the CDC criteria and a score above zero on the Chalder fatigue scale.4 With only minor modifications, the items used in this study were the same as those used by the Iowa Persian Gulf Study Group (1997). The study was limited by the lack of in-person interviews and examinations and by the nontraditional assessment of CFS.
The Iowa study (1997) surveyed 1,896 deployed and 1,799 nondeployed veterans who listed Iowa as their home state at the time of enlistment. The presence of a CFS-like condition was based on a combination of symptoms used in the CDC criteria (Fukuda et al. 1994) and scores on a fatigue scale (Chalder et al. 1993). The investigators found that the prevalence differed by 1.4% (95% CI 0.9-2.0) after adjusting for age, sex, race, branch of military, and rank. Study limitations were the use of self-reports of symptoms on a questionnaire and the lack of medical evaluations. Although rigorously conducted and analyzed, the study suffers shortcomings similar to those of the Canadian study.
Because the diagnosis of CFS depends entirely on symptoms, not on physical or laboratory findings, the prevalence is highly variable from study to study. In addition, some of the secondary studies reviewed were not limited to CFS but included fatigue or CFS-like illnesses. One primary study demonstrated a higher prevalence of CFS in deployed than in nondeployed veterans although the absolute difference in risk was very small (1.6% vs 0.1%).