OR of 2.32 (95% CI 1.02-5.27, p = 0.04) adjusted for age, sex, race, cigarette-smoking, duty type, service branch, and rank. Deployed veterans were slightly younger, less educated, less likely to be married, and of lower income, but the analysis adjusted for most of those factors. Strengths of the study include the population-based sampling strategy, blinding of evaluating physicians, and use of validated diagnostic criteria based on physical examination. Limitations include the potential for substantial selection bias due to modest participation rates—53% of deployed veterans and 39% of nondeployed veterans—and lack of information on potential exposures.

Using a different approach, Smith et al. (2000) examined all hospital records in DoD medical facilities from 1991 to 1997 to assess whether 551,841 Gulf War-deployed and 1,478,704 nondeployed active-duty military personnel were at increased risk for hospitalization with a diagnosis of fibromyalgia. During the 6-year period, 239 Gulf War veterans and 621 nondeployed veterans were hospitalized for fibromyalgia. Cox proportional-hazards models showed a slightly higher hospitalization rate for fibromyalgia among the deployed than among the nondeployed veterans (RR 1.23, 95% CI 1.05-1.43). The risk of hospitalization was 3 times greater for female veterans than for male veterans, twice as likely if the person had been hospitalized for any cause before the war, and more than twice as likely for Army veterans than veterans in other service branches. The authors attributed the increase to the DoD Comprehensive Clinical Evaluation Program (CCEP)—which began in June 1994 and ended in mid-1995—during which many veterans were admitted to the hospital only for purposes of evaluation. Before the inception of the CCEP, there was no difference in hospitalization for fibromyalgia between deployed and nondeployed veterans (RR 0.92, 95% CI 0.74-1.13); after CCEP in 1994, there was almost twice the rate of hospitalization for fibromyalgia (RR 1.76, 95% CI 1.39-2.22). CCEP participants were 26 times more likely to be hospitalized for fibromyalgia than were nonparticipants, and adding a CCEP covariate to the analysis resulted in a reduction in the risk for deployed veterans (RR 0.56, 95% CI 0.41-0.78). The Smith et al. study has the advantage of being a large population-based sample and having good statistical power for detection of an effect. Its major limitations are the inclusion of only active-duty personnel, changes in hospitalization rates for fibromyalgia in association with the practices of the CCEP, use of hospitalization data only from DoD medical facilities, lack of assessment of combat exposure or deployment stress, and the fact that fibromyalgia is rarely severe enough to warrant hospitalization.

The committee identified only one primary paper that looked specifically at CWP in deployed and nondeployed Gulf War veterans. A random sample of a population-based cohort of regular military and National Guard and reserve veterans (Iowa Persian Gulf Study Group 1997), 1896 deployed and 1799 nondeployed, who listed Iowa as their home state at the time of enlistment were surveyed in 1995-1996. Veterans were identified through the DMDC. The study was conducted through structured telephone interviews to determine the prevalence of CWP on the basis of responses to the SF-36. Gulf War veterans reported significantly more bodily pain than did nondeployed veterans (p < 0.01). In a followup study of a subset of this cohort 5 years after the baseline survey, Ang et al. (2006) conducted in-person followup examinations of 370 Gulf War veterans who had not met the case definition of CWP at baseline. The goal of the followup study was to identify predictors of delayed-onset CWP. Of the 370 veterans, 69 (18.6%) had met the classification criteria for CWP at the followup evaluation: 51 in the deployed group and 18 in the nondeployed group. According to a logistic multiple-regression model, CWP was significantly associated with perceived life stress (based on responses to the

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