Molecular epidemiology of adenovirus type 4 infections in US military recruits in the postvaccination era (1997-2003).

Background: Military recruits are at a higher risk of respiratory infection than their civilian counterparts. Continuous outbreaks of adenovirus (Ad)-associated acute respiratory disease were documented among US trainees before the implementation of serotype 4 (Ad4) and serotype 7 vaccines in 1971. The discontinuation of Ad vaccination programs in 1999 precipitated the reemergence of Ad in training sites, with Ad4 accounting for 98% of all diagnosed cases.
Methods: A total of 724 Ad4 strains isolated from recruits presenting with febrile respiratory illness at 8 training sites nationwide between 1997 and 2003 were genome typed by restriction enzyme analysis.
Results: Seven genome types were identified, all of which were distinct from the prototype Ad4p and the vaccine type 4p1. Results showed very different, and often stable, genome type distributions at different geographic sites, despite the homogeneity of the recruit source population.
Conclusions: The data support the hypothesis that reservoirs for Ad outbreaks are within recruit training sites or in their immediate environments, not in the incoming recruit population. Molecular characterization beyond serotype is critical to understanding the transmission dynamics of Ad infection in these unique susceptible populations and to the implementation of effective prevention approaches.