Background:: Theoretical studies have highlighted the importance of patterns of choice of sex partner in the transmission and persistence of sexually transmitted diseases (STDs).
Goal:: To describe reported patterns of sexual mixing according to numbers of sex partners in STD clinics.
Study Design:: Patients attending public health clinics in Seattle, Washington were interviewed about their own and their partners' behaviors.
Results:: Throughout, patterns of sexual mixing were weakly assortative. Across activity groups, many respondents believed their partners had no other sexual contacts. Those with three or more partners frequently perceived their partners to have three or more partners as well.
Conclusions:: Assortatively mixing persons of high sexual activity makes the persistence of STDs within a population likely (i.e., they act as a “core group”). Additionally, because mixing is not highly assortative (like with like), a steady trickle of infection from members of the core group will pass to other segments of the population.