exposures, especially “bathing in or drinking contaminated water (fumes, oil, chemicals),” remained significant after adjustment for associations of exposures with one another in a multiple logistic regression model.
One reference study discussed in Volume 4 examined Gulf War veterans who listed Oregon or Washington as their residence at the time of their deployment (McCauley et al., 1999a); two derivative studies were also described in that volume (Bourdette et al., 2001; Spencer et al., 2001). The Update committee did not identify any new studies that used this data set.
Investigators from the Portland Environmental Hazards Research Center examined numerous health outcomes in Gulf War veterans who were deployed between August 1, 1990, and July 31, 1991, and listed Oregon or Washington as their home state of record at the time of deployment; data was obtained from the DMDC (McCauley et al., 1999a).
Beginning November 1995 and ending in June 1998, a mailed questionnaire aimed to assess general health through symptom self-reports was distributed to a representative and random sample (n = 2343) of the total eligible 8603 Gulf War veterans mentioned above; the response rate was 48.4%. The study did not include a nondeployed comparison group. The next phase consisted of a clinical examination of the first 225 participants who showed differences between the symptoms they reported on questionnaires and the symptoms they reported at time of clinical examination. The greatest differences were in rash or lesions (4% agreement between questionnaire and clinical examination), gastrointestinal complaints (20% agreement), and musculoskeletal pain (35% agreement). The authors interpreted those findings as suggesting the likelihood of outcome misclassification due to reliance on self-administered questionnaires (McCauley et al., 1999a).
In Volume 4, Bourdette et al. (2001) was considered a reference study although it used the same data set as McCauley et al. (1999a). Bourdette and colleagues (2001) compared 244 potential cases of unexplained illness as evaluated through clinical examination with 113 potential controls from 799 of those eligible for the clinical study, and located participants who had completed the questionnaire described above. Findings from this study are discussed in Chapter 4.
A nested case-control analysis of the cohort examined 142 items related to Gulf War self-reported exposure 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 (drawn from those who completed the 1995-1998 questionnaire above). According to multivariate analysis, exposures most highly associated with unexplained illness were combat conditions, heat stress, and having sought medical attention during the Gulf War. When controlled for multiple simultaneous exposures, PB exposure, insecticides and repellents, and stress were not statistically significantly associated with unexplained illness leading 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