Direct Measurement of Human Immunodeficiency Virus Seroconversions in a Serially Tested Population of Young Adults in the United States Army, October 1985 to October 1987

Direct measurement of the incidence of infection with the human immunodeficiency virus (HIV)—the rate of new HIV infection — is vital if we are to understand better the dynamics of the current epidemic of HIV infection. Because soldiers are periodically and routinely screened for antibody to HIV, it is possible to measure the incidence of HIV infection directly in this large, demographically well-characterized population of young adults. To determine the incidence of HIV infection in this population, we examined test results reported by the U.S. Army's routine antibody-screening programs. During the first two years of the screening programs, the observed incidence of HIV infection was approximately 0.77 per 1000 persons per year. This rate was higher than expected on the basis of previously published estimates of seroprevalence in the Army (approximately 1.50 per 1000). On the basis of this annual incidence, and assuming it to be stable, we estimate that approximately 600 soldiers will become infected with HIV each year. The observed rate in the Army may be lower than the incidence of HIV infection in the corresponding demographic groups within the general U.S. population. MUCH of our knowledge about the epidemiology of infection with the human immunodeficiency virus (HIV) is based on surveillance of cases of the acquired immunodeficiency syndrome (AIDS) and on limited surveys of HIV seroprevalence and incidence in the population and among volunteers.^{1 2 3} Cases of AIDS, the clinical end stage of infection with HIV, indicate an epidemic of HIV infection that is many years old.^4,5 Surveys of the prevalence of HIV infection among volunteers have furthered our understanding of the HIV epidemic, but they are seriously biased by self-selection and exclusion factors, and they often focus on high-risk groups defined by…