Hepatitis E Seroprevalence and Seroconversion. Part 6
Second, the populations under investigation in these studies, although all from the United States, may have distinct differences. The military population may have a reduced risk for HEV exposure compared with that of the general US population. Factors such as living on a military installation, having standardized food suppliers on that installation, and emphasis on personal hygiene and sanitation in the military may minimize a service member’s exposure to HEV. In addition, 65% of our subjects were <30 years of age, with 42% of subjects being <25 years of age. Since HEV seropositivity has been shown to be positively associated with age and to have a cohort effect with higher rates in the past, differences in ages and collection dates of samples between each of the studies may be an additional explanation for differences in seroprevalence. In addition to the study limitations mentioned above, we did not have access to morbidity data collected in a standardized manner during the deployment that may have identified deployed military members with symptoms consistent with HEV infection. A study targeted to service members with known illnesses with a clinical presentation for hepatitis may have yielded higher seroconversion rates. In addition, data were not available on other HEV risk factors, such as contact with animals, diet, and travel.
Our study has several strengths. First, we had nearly the entire population of US military service members deployed to Afghanistan from which to sample, which made our study population representative of the entire cohort. Second, because of Department of Defense requirements to obtain predeployment and postdeployment serum samples, we had access to paired samples. Finally, even though the WRAIR assay differed from other assays, the incidence of anti‐HEV among US forces deployed to Afghanistan should not have been affected because any of the published assays would have detected seroconverters.
This study is the first (to our knowledge) to assess the incidence of HEV exposure among US military service members deployed to Afghanistan. Our findings of low anti‐HEV seroconversion during the deployment are reassuring. In addition, an encouraging finding was that even though deployment spanned several years, with undoubtedly varying levels of military infrastructure in Afghanistan, we did not see increased numbers of seroconverters among early deploying US forces. However, these findings only provide an overall assessment of risk; there may be certain deployed populations at increased risk of HEV infection. Service members who are embedded within local populations may have increased exposure to contaminated water, contaminated food sources, and unsanitary conditions, all of which have been shown to be risk factors for HEV transmission. In addition, these findings may not be generalizable to all deployment settings. Rapid or highly mobile deployments, which may lack the infrastructure to provide sanitary food and water supplies, deployments to regions where the disease is endemic, and deployments requiring frequent, close contact with local populations may all have high risks of HEV exposure. However, continued surveillance of HEV exposures and clinical cases are essential within the military, especially during deployments to new locations or to an immature theater setting.