Biomechanisms and Modeling Branch Air Force Research Laboratory Brooks Air Force Base, TX 78235-5250
In a seroepidemiologic study of the incidence and prevalence of hepatitis C virus (HCV) infection in 21,000 troops, Hyams et al. stated that the "relatively low prevalence of anti-HCV among troops who had served in the Vietnam War era is not representative of all populations of Vietnam veterans" (1, p. 769). The Air Force Health Study provides data from another population of Vietnam veterans.
The Air Force Health Study is a 20-year prospective cohort study initiated to address concerns among Vietnam War veterans about the consequences of exposure to Agent Orange and its contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin) (2). Because of the wide range of health, survival, and reproductive effects possible and the numerous associated covariates, our database includes information on many factors of interest, including the presence of antibodies to HCV. The Air Force Health Study population was not chosen by retirement status but is made up of pilots and members of air and ground crews who served in Southeast Asia during the Vietnam War. The average age in our cohort (58.5 years in 1997) is more than 11 years higher than that in the Hyams et al. cohort. Participants are all male and are predominantly enlisted personnel.
In 1997, the Air Force Health Study cohort, comprising 2,121 individuals (835 officers and 1,286 enlisted men), contained 27 men (five officers and 22 enlisted men) who were positive for HCV--a prevalence rate of 1.3 percent. The rate among enlisted men (1.7 percent) was nearly three times that among officers (0.6 percent). The 1.3 percent prevalence rate is lower than the 1.7 percent reported by Hyams et al. (1) for a cohort of 2,000 retirees with a mean age of 44 years. The rate among enlisted men in the Air Force Health Study was also lower than the 2.2 percent reported for enlisted retirees by Hyams et al. (1
). In addition, our rate is lower than the overall US prevalence of 1.8 percent (3
) and is equal to or less than that of all the individual demographic groups described by Alter et al. (4
). Interestingly, our prevalence almost matches that for the 50- to 59-year age group (1.3 percent vs. 1.4 percent) in the Third National Health and Nutrition Examination Survey (4
); in the latter data, prevalence peaks at age 3039 years and then decreases with age.
The Air Force Health Study data reinforce the idea that risk factors other than military duty are responsible for HCV infection (1, 4
), and they support the Hyams et al. data suggesting that Vietnam veterans do not have an increased risk of infection. However, they show not "a consistently higher prevalence of HCV infection in older service members" (1
, p. 769), as suggested by Hyams et al., but a prevalence that was lower in the distant past than in the recent past, as reported by Alter et al. (4
).
NOTES
Editor's note: In accordance with Journal policy, Hyams and colleagues were asked whether they wished to respond to this letter, but they chose not to do so.
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