In a primary study, Blanchard et al. (2006) sought to determine the prevalence of unexplained illnesses in Gulf War veterans 10 years after the Gulf War. The study applied CDC’s definition of chronic multisymptom illness (Fukuda et al. 1998).Data were collected from 1035 deployed veterans and 1116 nondeployed veterans. Participants were asked about symptoms in face-to-face interviews, and those who reported at least one symptom in each of three clusters—fatigability, mood and cognition, and musculoskeletal—were considered to meet the case definition. Cases were classified as severe if at least one symptom in each cluster was rated as severe. The investigators found that overall 29% of deployed participants and 16% of nondeployed participants met the criteria for chronic mutisymptom illness (OR 2.16, 95% CI 1.61-2.90); deployed veterans were more likely than nondeployed veterans to have severe chronic mutisymptom illness (OR 4.65, 95% CI 2.27-9.52), and among deployed veterans it was associated with a higher score on the Combat Exposure Scale (p < 0.001). Both deployed and nondeployed veterans who met the case definition had lower mean scores on the SF-36 for physical and mental health, more nonroutine clinic visits, more prescriptions, and were more likely to be using psychotropic medications, than deployed or nondeployed veterans without chronic mutisymptom illness. Veterans with chronic mutisymptom illness were also more likely than veterans without it to also have fibromyalgia, CFS, symptomatic arthralgia, dyspepsia, metabolic syndrome, PTSD, anxiety disorders, major depression, nicotine dependence, alcohol dependence (deployed veterans only), and more than one psychiatric diagnosis during the year preceding the examination. The study was limited by low participation rates and the self-reporting of symptoms, but it provided evidence that the cluster of symptoms used to define chronic mutisymptom illness persisted in Gulf War veterans 10 years after the war.

Ozakinci et al. (2006), in a secondary study, also investigated widespread symptomatic illness in Gulf War veterans. Participants were identified from the VA Gulf War Health Registry, contacted twice (in 1995 and 2000), and asked to respond to symptom survey questionnaires. Statistical analyses were conducted to assess changes in symptoms over time. No significant changes were found in the cohort in symptom number or severity. Thus, Gulf War Health Registry veterans 10 years after deployment continued to experience significant symptoms. Limitations of the study include the problem of generalizability to all Gulf War veterans—the study included only veterans in a registry, and there was no nondeployed comparison group—and the possibility of reporting bias because of the self-reporting nature of the questionnaire.

Self-reports of health status in Australian Vietnam veterans 20-25 years after the war, and the impact of combat exposure, were investigated. O’Toole et al. (1996b) used the Australian Bureau of Statistics Health Interview Survey questionnaire to interview in-person a random sample of Army veterans posted to Vietnam during 1964-1972 and compared the veterans with the general Australian population. A 21-item combat exposure index was also used to measure the relationship between combat and physical health. Combat exposure was related to recent but not chronic symptoms, signs, and ill-defined conditions. Comparison of Australian Vietnam Veterans with the Australian population for prevalence of self-reported symptoms, signs, and ill-defined conditions, adjusted for response bias, yielded an RR of 2.77 (99% CI 1.88-3.66).

In the first of three primary hospitalization studies, Gray et al. (1996) used a retrospective cohort and data from DoD hospitals for the period 1991-1993. The study examined hospitalizations of 547,076 Army, Navy, Marine Corps, and Air Force Gulf War veterans and 618,335 nondeployed era veterans. Multivariate logistic-regression analyses yielded ORs of less than 1 for ill-defined conditions for all 3 years. The authors noted that in an attempt to reduce the



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