The Centers for Disease Control and Prevention defines a "notifiable" disease as one for which regular, frequent, and timely information on individual cases is considered necessary for the prevention and control of the disease (Centers for Disease Control and Prevention 2011). Of the more than 50 infectious diseases designated as notifiable at the national level during 2007, the newly reported incidence rates of six diseases are discussed here: acquired immunodeficiency syndrome (AIDS), chlamydia, gonorrhea, syphilis, tuberculosis, and Lyme disease.
The incidence of several sexually transmitted diseases—AIDS, gonorrhea, and syphilis—within the youth and young adult population (i.e., 15- to 24-year-olds) was lower in1995 than in 2000. However, the incidence of AIDS increased between 2000 and 2007, the incidence of gonorrhea increased between 2004 and 2007, and the incidence of syphilis increased between 2003 and 2007. There were 2,666 reported cases of AIDS among youth and young adults in 1995; a reported 1,567 cases in 2000; and 2,305 cases in 2007. The number of AIDS cases was lower in 2000 than in 1995 despite an increase in the youth and young adult population over the same time period (see table 1). The incidence rate of AIDS in the youth and young adult population was 7.5 per 100,000 in 1995, compared with 4.2 per 100,000 in 2000. Between 2000 and 2007, the rate gradually increased to 5.4 per 100,000. There were 228,698 cases of gonorrhea in 1995 in the youth and young adult population, compared with 189,629 cases in 2004 and 209,678 cases in 2007. Accordingly, the incidence rate declined between 1995 and 2004 (from 645.0 to 460.2 cases per 100,000), but subsequently increased to 494.1 cases per 100,000 in 2007. Similarly, there were 4,860 cases of syphilis in 1995 among the youth and young adult population, compared with 1,182 cases in 2003 and 2,481 cases in 2007. The incidence rate dropped from 13.7 per 100,000 in 1995 to 2.9 per 100,000 in 2003, before rising again to 5.9 per 100,000 in 2007.
The number of cases and the incidence rate of chlamydia (the most common sexually transmitted disease) have also increased in recent years. In 2000, there were 508,736 cases of chlamydia among 15- to 24-year-olds, or 1,349.4 per 100,000. By 2007, the number of cases had increased to 779,280, or 1,836.4 per 100,000.
The prevalence of common nonsexually transmitted diseases among youth and young adults also varied between 1995 and 2007. There were 994 cases of Lyme disease in this population in 1995, compared with 2,833 in 2007, an increase from 2.8 to 6.7 cases per 100,000. The number of cases and the incidence rate of tuberculosis among youth and young adults was higher in 1995 (1,703 cases or 4.8 per 100,000) than in 2007(1,581 cases or 3.7 per 100,000).