examination (after exclusion of established diagnoses) were defined as constituting cases. Controls were those who at the time of clinical examination had no history of case-defining symptoms during or after their service in the Gulf War. In an analysis of the 241 cases vs 113 controls, investigators found, at medical evaluation, small but statistically significant deficits in cases on some neurobehavioral tests of memory, attention, and response speed. Cases also were significantly more likely to report increased distress and psychiatric symptoms (Storzbach et al. 2000). Finally, more than half the veterans with unexplained musculoskeletal pain met symptom-based criteria for fibromyalgia, and a large proportion met symptom-based criteria for CFS (Bourdette et al. 2001). Bourdette and colleagues also undertook a factor analysis, which yielded three symptom-based factors: cognitive-psychologic, mixed somatic, and musculoskeletal. These case-control studies and others from this cohort are reviewed further in Chapter 5.
Another nested case-control analysis of the population-based cohort examined exposures that might account for cases of unexplained illness (Spencer et al. 2001). The sample consisted of 241 veterans with unexplained illness and 113 healthy controls. In multivariate analysis, exposures most highly associated with unexplained illness were combat conditions, heat stress, and having sought medical attention during the Gulf War. Exposure to PB, insecticides and repellents, and stress was not statistically significantly associated with unexplained illness when multiple simultaneous exposures were controlled for. Those findings led investigators to conclude that unexplained illnesses were not associated with cholinesterase-inhibiting neurotoxic chemicals. One strength of this study was its elimination of numerous self-reported exposures (such as anthrax and botulinum toxoid vaccines) with questionable validity as determined by lack of test-retest reliability or time-dependent information (for example, chemical weapon exposure reported by precombat veterans or postcombat veterans who could not have been so exposed) (McCauley et al. 1999a).
The state of Kansas established the Kansas Persian Gulf War Veterans Health Initiative to determine the patterns of veterans’ health problems in the state. Using lists of eligible veterans from DOD, Steele and colleagues (2000) conducted a population-based survey of veterans who listed Kansas as their home state of record. A stratified random sample of 3,138 was selected, from which 2,396 were located with instate contact information. The survey, mailed out in 1998, asked about 16 specific medical or psychiatric conditions, 37 symptoms, service branch, locations during the Gulf War (including whether the veterans were notified about the Khamisiyah demolitions), and vaccinations. Kansas Gulf War veterans, in comparison with Kansas nondeployed veterans, reported greater prevalence of 10 physician-diagnosed conditions: skin conditions, stomach or intestinal conditions, depression, arthritis, migraine headaches, CFS, bronchitis, PTSD, asthma, and thyroid condition. Using their own definition of Gulf War illness, which was similar to that used by the Centers for Disease Control and Prevention (CDC) (Fukuda et al. 1998), the investigators found that its prevalence was most associated with the period and location in the gulf in which veterans served. It was least prevalent in the period before the war, for example. Overall, the multisymptom illness was found in 34% of deployed, 12% of nondeployed who had received vaccines, and 4% of nondeployed who did not receive vaccines. The study concluded that excess morbidity is tied to characteristics of Gulf War service and that vaccine exposure might contribute to onset of multisymptom illness.