Vaccine-preventable adenoviral respiratory illness in US military recruits, 1999-2004

Abstract

Background and methods: The high burden of respiratory infections in military populations is well documented throughout history. The primary pathogen responsible for morbidity among US recruits in training was shown to be adenovirus. Highly efficacious oral vaccines were used for 25 years, but vaccine production ceased in 1996, and available stores were depleted by early 1999. Surveillance for acute febrile respiratory illness was performed at eight military recruit training sites throughout the United States from July 1999 through June 2004 to document rates after loss of the vaccines. Laboratory diagnoses complimented the surveillance efforts.

Results: Over the 5 years, nearly 12 million person-weeks were followed and an estimated 110,172 febrile respiratory illness cases and 73,748 adenovirus cases were identified. Rates of illness were highest at the Navy and Air Force training centers, with average annual rates of 1.20 and 1.35 cases per 100 recruit-weeks, respectively. Adenoviral-associated illness rates peaked in weeks 3-5 of training, depending upon service.

Conclusions: The burden of adenoviral illness among US recruit populations has returned to high levels since loss of the vaccines. Restoration of an effective adenovirus vaccine effort within the military is anticipated by 2008, potentially reducing the adenovirus morbidity suffered in this vulnerable population. Efforts to determine the burden of adenovirus and potential benefits of vaccination in civilian populations are being renewed.

Figure 1. Estimated adenovirus infection rates by service, 1999-2004

Adenovirus infection rates by service (July 1999 to June 2004), as estimated by projecting the percentage of adenovirus positive among tested samples to the total counted febrile respiratory illness cases. Rates are expressed as number of cases per 100 recruit-weeks.

Figure 2. Proportion of adenovirus cases by week of training

Note that Marines have 12 weeks of training; therefore, week 9+ for the Marine Corps represents 4 weeks of person-time. During week 5, Air Force recruits are in the field, and capture difficult.

Figure 3. Army total febrile respiratory illness (FRI) and adenovirus (ADV)-specific FRI rates by total population onboard, 1999-2004

Graphic representation of the relationship between total recruit population onboard (blue line) with cases of FRI (yellow) and cases of adenoviral illness (red). As can be seen, when numbers of recruits being trained increase (crowding), rates of illness increase. The correlation coefficient between FRI rates and size of the populations in training was 0.263. Correlation between Ft. Jackson FRI rates and mean ambient temperature (not shown) at that site was 0.559.