P.L. 104-146 also calls on the Institute of Medicine (IOM) to "conduct an evaluation of the extent to which State efforts have been effective in reducing the perinatal transmission of the human immunodeficiency virus, and an analysis of the existing barriers to the further reduction in such transmission." In its analysis, the committee has found it helpful to consider a chain of factors affecting perinatal transmission, as illustrated in Figure 1.

Disease screening is one of the most basic tools of modern public health and preventive medicine. As screening programs have been implemented over the years, a substantial body of experience has been gained. In practice, when screening is conducted in contexts of gender inequality, racial discrimination, sexual taboos, and poverty, these conditions shape the attitudes and beliefs of health system and public health decision makers as well as patients, including those who have lost confidence that the health care system will treat them fairly. Thus, if screening programs are poorly conceived, organized, or implemented, they may lead to interventions of questionable merit and enhance the vulnerability of groups and individuals. Through the experience with public health screening programs, a series of characteristics of well-organized public health screening programs has evolved (Wilson and Jungner, 1968).

The committee's summary of the relevant characteristics is as follows:

1. The goals of the screening program should be clearly specified and shown to be achievable.
2. The natural history of the condition should be adequately understood, and