A small proportion of people experiencing a sexually transmitted disease (STD), who are frequently infected or often transmit the infection, has been referred to as the "core." Though a prominent paradigm in the epidemiology of STDs, there is confusion about the meaning of the core. The term has been used to refer variously to people who are infected a large proportion of the time, infect more than one other person, are repeatedly infected, or are prostitutes or their clients and to geographic areas with large numbers of cases. Three perspectives that have contributed to the development of the concept of an STD core were identified: mathematical, clinical-epidemiologic, and sociocultural. These different perspectives share the common aim of identifying strategic points of intervention to reduce STDs. The value of the concept of an STD core will ultimately derive from its utility in lowering STD rates.
