100,000 persons in the United States versus 3.0 cases per 100,000 in Sweden (CDC, DSTDP, 1996; Swedish Institute for Infectious Disease Control, unpublished data, 1996). Because actual U.S. rates are estimated to be approximately twice the reported rate, the U.S. rate is 100 times the reported rate in Sweden. Similarly, the reported incidence of gonorrhea in Canada in 1995 was 18.6 cases per 100,000, or approximately 12 percent of the U.S. rate (Laboratory Centre for Disease Control, Canada, unpublished data, 1996). In addition, the rate of primary and secondary syphilis in the United States was 6.3 cases per 100,000 persons versus 0.4 cases per 100,000 persons in Canada. Therefore, rates of curable STDs, including gonorrhea, syphilis, and chancroid are many times higher in the United States than in other developed countries. The differences in rates of viral STDs between the United States and other developed countries, however, appear to be much smaller. Data for viral STDs are much more limited than for bacterial STDs, but do not suggest major differences. For example, a cohort of young Swedish women studied over a 16-year-period showed a cumulative incidence of genital herpes that was comparable to the age-specific increases in herpes simplex virus type 2 antibodies seen during the approximately the same period in U.S. women (Christenson et al., 1992; Johnson et al., 1993). Potential explanations for the observed differences between the United States and other developed countries in rates of curable STDs are presented in Chapter 3.

Further, many new STDs have been discovered or have newly arisen during the antibiotic era. Of these "modern" STDs, some, including HIV infection, human papillomavirus infection, and hepatitis B virus infection, are viral infections that are incurable and are now recognized as major preventable causes of death and disability. The bacterial STDs, such as gonorrhea and syphilis, can be easily diagnosed and successfully treated; others, such as chlamydial infection, are curable but will require a much stronger, coordinated national effort to be brought under control.

Broad Scope and Impact of STDs

STDs affect persons of all racial, cultural, socioeconomic, and religious groups in the United States. Persons in all states, communities, and social networks are at risk for STDs. The estimated incidence and prevalence of major STDs are summarized in Table 2-1.

The term "STD" is not specific for any one disease but denotes the more than 25 infectious organisms that are transmitted through sexual activity and the dozens of clinical syndromes that they cause (Appendix A). With STDs, one infectious organism does not cause one syndrome; rather, there is a matrix of infectious organisms and associated syndromes. For example, some syndromes, such as pelvic inflammatory disease, can be caused by a number of organisms, including Neisseria gonorrhoeae, Chlamydia trachomatis, and other bacteria. Urethritis (inflammation of the canal leading from the urinary bladder) in men is frequently



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