Simmons et al. 2004; Simmons et al. 2004; Unwin et al. 1999; Unwin et al. 1999) Canada (Goss Gilroy Inc. 1998), Australia (Kelsall et al. 2004), or Denmark (Ishoy et al. 1999)—have found that several years after deployment those deployed report higher rates of respiratory symptoms and respiratory illnesses than nondeployed troops. Of particular interest is the UK cohort study reported in Nisenbaum et al. (2004) and Unwin et al. (1999), which found substantially higher prevalences of respiratory symptoms and self-reported respiratory disease among those deployed in the Gulf War than among those deployed in another war theater, Bosnia.
Several studies examined respiratory outcomes specifically associated with chemical exposures experienced by Gulf War veterans, whereas the studies discussed above examined respiratory outcomes associated with deployment. The study of Cowan et al. (2002), which used objective exposure measures and methods2, found associations between oil-well fire smoke and doctor-assigned diagnosis of asthma in veterans. A limitation of the study is that the participants were self-selected. The other key Gulf War study of oil-well fire smoke, which was based on the Iowa cohort (Lange et al. 2002), found no relationship between the same objective exposures and respiratory health outcomes; it had the advantage of avoiding the potential selection biases of the Cowan et al. study. However, its definitions of respiratory diseases were based entirely on self-reports of symptoms and cannot be viewed as adequate. The study by Smith et al. (2002) found no statistically significant associations between the same objective measures of exposure to smoke from oil-well fires and later hospitalization for asthma, acute bronchitis, chronic bronchitis, or emphysema. However, the participants were all active-duty veterans; most young adults are seldom hospitalized for those diagnoses, so most cases would not be expected to be captured.
The study by Gray and collaborators (1999) found a small increase in postwar hospitalization for respiratory system disease associated with modeled exposure to nerve agents at Khamisiyah. Limitations of that study probably include substantial exposure misclassification based on DOD exposure estimates that were later revised, lack of control for tobacco-smoking, lack of a clear dose-response pattern, and limited biologic plausibility of effects on the respiratory system in a setting in which no effect on nervous system diseases was seen. Karlinsky et al. (2004) found no statistically significant associations between pulmonary-function measures and exposure to nerve agents at Khamisiyah on the basis of the revised DOD exposure estimates.
In conclusion, as is the case for a number of other organ systems, respiratory symptoms and self-reported health outcomes are strongly associated with Gulf War deployment in most studies addressing this question that use comparison groups of nondeployed veterans. However, studies with objective pulmonary-function measures find no statistically significant association between respiratory illness and disease and Gulf War deployment in the four cohorts in which this has been investigated; thus, the studies leave an uncertain clinical interpretation of the increased symptoms and self-reported diseases.
Exposure to smoke from oil-well fires was estimated by linking troop locations with modeled oil-fire smoke exposure. National Oceanic and Atmospheric Administration researchers modeled exposure on the basis of meteorologic and ground-station air-monitoring data (Draxler et al. 1994; McQueen and Draxler 1994) with a spatial resolution of 15 km and a temporal resolution of 24 hours. DOD personnel records were used to ascertain each study subject's unit and dates of service. Only Army personnel were included in the study because their location data were more precise. Two exposure measures were used: cumulative smoke exposure (the sum of the estimated concentration on all days when each subject was in the Gulf War Theater) in milligram-days per cubic meter (mg-day/m3), with referent exposure < 0.1 mg-day/m3 per day; and number of days when the subject was exposed at 65 μg/m3 or greater.