starting in the mid-1970s with the introduction of the national gonorrhea control program. A disproportionate share of the decline occurred among older white populations, with infection rates remaining relatively high among minority groups and adolescents. In 1996 the Centers for Disease Control and Prevention (CDC) reported 325,000 new cases of gonorrhea (CDC, 1999b). Because previous investigations have shown that only about half of all diagnosed gonorrhea cases are reported to public health authorities, total gonorrhea infections are estimated to be 650,000 in Table 2.

SOURCE: Kaiser Family Foundation, 1998.

HIV infection trends in the United States show that in the mid-1970s HIV was transmitted primarily among homosexual and bisexual men. The virus entered the injection-drug-using populations in the 1980s and rapidly spread during that decade. Limited heterosexual transmission occurred until the 1980s. Since 1989 the greatest proportional increase in reported AIDS cases has been among heterosexuals, with this trend expected to continue (Rosenberg, 1995). New methods of estimating HIV incidence and prevalence (Holmberg, 1996) yielded an estimate of 41,000 new HIV infections annually, with between 700,000 and 800,000 prevalent HIV infections. The introduction of protease inhibitors may increase the number of prevalent infections by extending the life of HIV-infected people. Approximately half of the incident and three-quarters of prevalent infections were estimated to have been sexually transmitted. Globally, the incidence of HIV is much higher than in the United States, with an estimated 5.8 million new infections annually and more than 30 million persons currently living with HIV (UNAIDS, 1998). More than 90 percent of the global total has been spread sexually.

An important priority for future research is to improve the accuracy of these estimates. Most STD incidence and prevalence estimates are derived