This article describes and assesses the epidemiology of AIDS and HIV infection in Costa Rica. A total of 283 AIDS cases were reported in the country between 1983, when the first cases were diagnosed, and the end of August 1991. This placed Costa Rica third among the seven Central American countries--both in terms of cumulative AIDS incidence and the cumulative number of cases. Despite a continued small number of hemophilia and transfusion-associated AIDS cases, screening of blood and blood products has provided a high degree of safety for the blood supply. The high male:female ratios of reported AIDS cases (11:1) and HIV infections (14:1) and the high proportion of AIDS cases (72%) transmitted by male-to-male sexual contact give grounds for considering Costa Rica to be a Pattern I country--one where the disease is transmitted, primarily among homosexual/bisexual males. However, increasing numbers of heterosexual and perinatal cases, high rates of HIV infection among pregnant women, and existing patterns of bisexuality are consistent with a possible shift toward a Pattern I/II epidemic.
