This section concentrates on all-cause hospitalization to determine whether there is an excess risk of hospitalization among Gulf War veterans. Hospitalizations for specific causes, although noted here, are discussed in more detail throughout the report. The primary studies are summarized in Table 5.21.
Studies of differences in rates of hospitalization between deployed and nondeployed populations can indicate excess morbidity associated with Gulf War service. Although they are less able to detect subtle differences than studies that measure morbidity directly or examine outpatient morbidity, they are less crude than studies of differential mortality. Overall hospitalization (that is, for all causes) and cause-specific hospitalization were the subject of several large studies, mostly of active-duty personnel discharged from DOD hospitals.
The first study (1991-1993) compared the hospitalizations of almost 550,000 Gulf War veterans and almost 620,000 nondeployed veterans and found no consistent differences over time in all-cause hospitalizations after the war (Gray et al. 1996). There were increased rates of hospitalization of Gulf War veterans in some diagnostic categories in some years (for example, neoplasms in 1991 and diseases of the blood in 1992), but the rates were not consistently increased, except rates of hospitalization for mental illness in 1992 and 1993. The study also found increased hospitalization, in 1991 only, for the broad category “genitourinary system diseases”. The authors found, more specifically, that the increase was due to female veterans being hospitalized for inflammatory diseases of the ovary, fallopian tube, pelvic cellular tissue, and peritoneum. Those increases could be explained by deferral of care, postwar pregnancies, and some psychiatric disorders (alcohol dependence, nondependent drug abuse, and adjustment reactions). The study also examined reasons for separation from the armed services in 1991-1993. Contrary to expectations, the study found that deployed veterans were less likely than nondeployed veterans to have separated for reasons of medical disqualification, dependence or hardship, entry into officer programs, retirement, or behavior or performance failure.
A second hospitalization study extended the study period (1991-1996) and re-examined the dataset to search for excess hospital admissions for unexplained illnesses (Knoke and Gray 1998). The authors reasoned that the first study might have missed hospitalizations for a new or poorly recognized syndrome.
In the third study, Gray et al. (2000) examined hospitalizations (1991-1994) of active-duty, reserve, and former military personnel who had been deployed to the Gulf War. The study examined hospitalizations at DOD, VA, and nonfederal California hospitals to eliminate potential bias related to veterans’ seeking care outside DOD and VA facilities. Because of the unreliability of state-of-residence data in DOD and VA datasets, the authors could not directly compare rates of hospitalization among the three sources. Rather, they compared PMRs of hospitalization-discharge diagnoses (14 diagnostic categories from ICD-9) in Gulf War-deployed and nondeployed veterans. PMRs of most disease categories were not increased. However, four categories were increased in VA patients (but not in active-duty military or California veterans): respiratory (PMR 1.19, 95% CI 1.10-1.29), digestive (PMR 1.12, 95% CI 1.05-1.18), skin (PMR 1.14, 95% CI 1.00-1.27), and ill-defined diseases (PMR 1.24, 95% CI 1.16-1.33). Among