clinic-based and community-based services. In another holistic approach to prevention, Stryker and colleagues (1994) identified several fundamental precedents that need to exist before effective HIV prevention is possible. These factors are: (a) sound policies that promote HIV risk reduction; (b) access to health and social services, including condoms, needles, syringes, and information; (c) interventions shown to motivate behavior change; (d) community-based organizations capable of reaching persons at risk; and (e) development and diffusion of technologies to interrupt HIV transmission. Similar conditions are probably necessary for the prevention of other STDs.

In terms of the mathematical model previously described, current technology can reduce , the mean probability of transmission per exposure, and D, the mean duration of infectiousness, to zero. This means that we have the technology and resources to interrupt transmission and greatly reduce many STDs in the United States. In this chapter, the committee describes the complex behavioral problems involved in reducing and c ("the effective mean rate of partner change") and in ensuring that individuals have access to, and make use of, the technologies that can reduce the efficiency of transmission and duration of infectiousness. The committee also evaluates the ability to effectively and efficiently screen for and treat STDs and describes available effective methods for preventing STDs. It should be noted that most of the behavioral interventions discussed in this chapter focus more on reducing efficiency of transmission than on reducing the rate of partner change. This is because many studies of behavioral interventions use consistent condom use as the primary behavioral outcome. In actuality, many behavioral interventions have multiple objectives that include reducing the rate of partner change. Examples of this are school-based interventions that seek to delay the onset of sexual intercourse and also promote condom use. Nevertheless, research on behavioral interventions to reduce the rate of partner change have been underemphasized. It should be noted that reducing the rate of partner change or the patterns of partner selection may affect the dynamics of how groups at differing risk for STDs subsequently interact in populations (Morris, 1996).

The question implicit in the subsequent sections is a perplexing and disturbing one: Why has the United States been unsuccessful in significantly reducing or eliminating a group of diseases that costs thousands of lives and billions of dollars annually in health care costs, despite the fact that effective tools are available?

Figure 4-2 depicts the levels of potential breakdown in steps required to prevent STDs. In regard to the third level (from the top of Figure 4-2), there is currently no way to influence the development of symptoms of STDs. All the other levels, however, represent a point for preventive interventions. Individual and population-level interventions are needed to (a) reduce individual risk behaviors and high population prevalence of STDs, both of which increase exposure to STDs; (b) promote safe practices and protective methods, such as condom use, necessary to reduce acquisition of an STD by those exposed; (c) educate the

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