Hepatitis E Seroprevalence and Seroconversion. Part 2
Although the seroprevalence of anti‐HEV in Afghanistan is not known, hepatitis E is considered to be endemic in that country. Large numbers of hospitalizations for hepatitis and other enterically transmitted diseases during Soviet operations in Afghanistan during the 1980s and a recent HEV outbreak in Laghman Province generated concern that US service members deployed to Afghanistan may be at risk for HEV infection. In addition, outbreaks of hepatitis E have been reported in several other military environments in Chad, Djibouti, Nepal, Ethiopia, Somalia, India, and Pakistan. In most of these outbreaks, contaminated drinking water was usually implicated. High attack rates in areas where hepatitis E is endemic and lengthy convalescent periods lasting 6 or more weeks contribute significantly to the loss of soldier duty days and seriously impact military operations. Sporadic and epidemic hepatitis E (likely caused by genotype 1) in Afghanistan has the potential to render combat troops combat ineffective for weeks.
To address these concerns, we conducted a retrospective cohort serosurvey of US service members who were deployed to Afghanistan as part of Operation Enduring Freedom. The survey was designed to estimate the baseline anti‐HEV prevalence, determine the incidence of HEV infections during deployment, and determine the risk factors for HEV seroprevalence and seroconverison.
Methods
Study population and design.The Defense Medical Surveillance System (DMSS) contains medical, demographic, occupational, service, and deployment data about US service members beginning at the time they apply and continuing for the duration of their military careers [39]. DMSS deployment rosters are provided by the Defense Manpower Data Center. Using DMSS, we identified the entire cohort of service members who were deployed to Afghanistan between 1 January 2002 and 31 December 2006, which consisted of 108,218 personnel.
The Department of Defense Serum Repository maintains serum samples collected from service members for the purpose of mandatory human immunodeficiency virus (HIV) testing and operationally required predeployment and postdeployment samples. The Department of Defense Serum Repository was queried to identify which service members from the cohort had at least 2 serum samples on file at the repository. The cohort was further restricted to the 40,162 personnel whose samples were collected within the 180 d preceding and following the deployment start and end dates, respectively. From this remaining cohort, we selected a random sample of 1500 subjects for the study.
Demographic, deployment, and medical encounter data for the 1500 subjects were obtained from DMSS. Specifically, data on age, race or ethnicity, education level, birth location, home location at entry, service, deployment history, military occupational history, and responses on the Postdeployment Health Assessment Form (form DD2796, which is completed within 30 d prior to or 90 d after the end of the deployment) were extracted from DMSS. Home locations at entry were categorized into 9 US divisions based on US census division categories. In addition, home locations at entry were categorized as urban or rural on the basis of the rural‐urban continuum codes developed by the US Department of Agriculture. Data on all possible hepatitis‐related medical encounters (ICD‐9‐CM codes 070.00–070.99 [hepatitis diagnosis], 009.00–009.99 [ill‐defined intestinal infections], 787.00–787.99 [symptoms involving the digestive system], 780.6 [fever], 783.0 [anorexia], and 789.1 [hepatomegaly]) that occurred before or after the deployment were also obtained from DMSS.