Gonorrhea Transmission Dynamics and Control

It is obvious that the characteristics of a specific disease must be understood thoroughly in order to model that disease. Gonorrhea incidence, transmission, symptoms, complications and treatments are described in sections 1.1 and 1.2. Various current and potential control procedures for gonorrhea are described in section 1.3. Among the several basic types of models for infectious diseases described in section 1.4, it is apparent that one type is suitable for gonorrhea. A brief description of previous work on the mathematical modeling of gonorrhea is given. The concepts of the contact number and the infectee number are described in section 1.5.

The population which needs to be described by a model for the transmission of gonorrhea consists of those sexually active people who could be infected by their contacts. The model in Chapter 2 assumes that this population is homogeneous and uniform; however, that model is too simple since the population is really quite heterogeneous. A suitable model should allow for heterogeneity by incorporating many groups. The division into groups could be done according to differences in sex, sexual contact rates, sexual behavior, age, geographic location, socioeconomic status, etc. For example, some individuals are more active sexually than others in the sense that they have more frequent changes of sex partners. Some infected people, especially women, are essentially asymptomatic and do not seek treatment while others have symptoms which cause them to seek treatment.

In the early 1970s, the prevalent idea was that “gonorrhea is everybody’s problem”. It was recognized that everyone who was sexually active could get gonorrhea and, consequently, the screening program in the United States started in 1972 was designed to identify asymptomatic women by doing culture testing of as many women as possible. This screening program has been described in section 1.3.

Although sexually transmitted diseases are a major health problem among homosexuals, there is little transmission between the homosexual population and the heterosexual population (WHO, 1978; Wiesner and Thompson, 1980). Here we concentrate on a heterosexual population subdivided into women and men since the characteristics of gonorrhea are different for the two sexes. Although the groups of women and men considered here are highly active sexually, the results are more general since it was shown in Chapter 4 that changes in prevalence in the noncore group are directly related to changes in prevalence in the core group.

In Chapters 4 and 5, the population was divided into two groups. Here the population is divided according to sex, the level of sexual activity and whether the infections are symptomatic or asymptomatic. There are eight groups representing the eight combinations, such as the male-highly active-asymptomatic group. This population dynamics model is used to compare the effectiveness of six control methods for gonorrhea involving population screening and contact tracing of selected groups. A condensed version of the results in this chapter appeared in a paper (Hethcote, Yorke and Nold, 1982).