THE SOCIAL NETWORKS APPROACH IN STD EPIDEMIOLOGY

During the past decade an important trend in STD epidemiology research has focused on the role of sexual networks in the spread of STIs in populations. Findings demonstrated that in the United States, the higher rates of sexual contact between the “core” group and the “periphery” among African Americans facilitate the spread of infection overflow into the African American general population; whereas the “sexual segregation” of African Americans from other racial-ethnic groups results in STIs remaining inside this population.^{15, 16} Other studies have shown that linkages between sexual networks are necessary for the spread of STIs across sexual networks¹⁷; that so called “core groups” appear to be important in the spread of STIs and in their prevention^18–20; and that the sexual transmission of sexually transmitted diseases (STDs) and HIV beyond core groups may depend on people who have sexual intercourse with members of core groups and with members of the general population—so called “bridge populations.”¹⁷ Studies in Thailand and other populations revealed that large proportions of men in certain occupations, such as truck drivers, the police, and the military tend to function as “bridges” between female sex workers and their wives or girlfriends.^{21, 22} However, one study conducted in Seattle found the proportion of infection attributable to bridge populations to be remarkably small; with most of the disease burden for gonococcal and chlamydial infections in both high prevalence and low prevalence subpopulations being attributable to mixing within the subpopulation or to direct mixing with members of high prevalence subpopulations.²³ It appears that bridge populations play a very important part in the introduction of infection into subpopulations, once the infection is introduced, most of the disease burden is attributable to mixing within the subpopulation.

Other studies conducted in Canada reveal that sexual network patterns involved in STD epidemics vary across phases of epidemics²⁴ and that during later phases of STD epidemics, the majority of sexual networks involved in the epidemic are not restricted to one geographic area²⁵; frequent contact between network members from a small group of northern reserves and individuals in the major southern population centre of Winnipeg have formed bridges of transmission between these communities. Similarly, a study of elimination and reintroduction of primary and secondary syphilis in Seattle showed that characteristics of persons with primary and secondary syphilis varied across epidemic spread, elimination, and reintroduction periods.²⁶ There were significant differences between cases during the various epidemic phases with respect to age, sex, ethnicity, drug use, and involvement with commercial and anonymous sex. Moreover, during all phases, imported cases differed from locally acquired cases with respect to age, sex, ethnicity, and drug use behaviours.

One network pattern that has received increasing research attention in recent years is concurrent partnerships, or sexual partnerships that overlap over time.²⁷ Concurrent partnerships accelerate the spread of an STI through a population by removing the protective factors of time and sequence inherent in serial monogamy.

Sexual networks and patterns of sexual partnership formation and dissolution constitute a major mechanism of action through which the political economy and the sociolegal system influence the rate of spread of STI in a population; availability, accessibility, and utilisation of appropriate health care, and availability and utilisation of condoms being others.

CREATION, MAINTENANCE, AND EVOLUTION OF CORE GROUPS

Sexual networks that are highly critical to the rate of spread of STI include sex work; exchange of sex for gifts, material needs or drugs; and anonymous sex. The creation, maintenance, and expansion of sex in exchange for money or other goods appears to be highly sensitive to changes in political economy and the sociolegal system. Internal conflicts, war, economic crises, and social collapse are accompanied by the establishment of major sex markets or the expansion of existing ones. For example, in Moscow, Russia, before the August 1998 economic crisis the number of female sex workers was estimated at 15 000–30 000; following the crisis this number increased to 30 000–90 000.²⁸ Similarly, in Jakarta and Surabaya, Indonesia, between 1997 and 1998—during which time the monetary crisis occurred—the percentage of female sex workers who were less than 20 years of age increased by 38% and 125% respectively; the percentage of female sex workers with less than 12 months' experience increased by 28% and 130% during the same period in these two cities.²⁹ A decade of conflict in the Balkan region and the poverty of post communist eastern Europe have created a major network of trafficking in women which reaches across eastern Europe, Balkans, the Middle East, and Western Europe.³⁰ Globalisation, characterising many social, economic, and behavioural patterns, includes sex work and expands the volume of sex workers.^{31, 32}

The political economy and the sociolegal system and any changes in them systematically impact lower socioeconomic status, minority groups to a greater extent than others. Sociolegal systems tend to reinforce existing hierarchies and protect the privileged. Thus, social parameters often create the context which facilitates the creation, maintenance, and expansion of sexual networks that cause rapid spread of STD among minority racial, ethnic, and socioeconomic groups and in less developed societies. The same context associates longer duration of infection with the less privileged groups and less privileged societies through differential access to, and differential utilisation of, good quality STD care. A detailed description of the sociopolitical context in which African Americans live in the rural southeastern United States powerfully elucidates how contextual features including racism, discrimination, limited employment opportunity, and resultant social and economic inequity may promote sexual network patterns that transmit STIs.³³

Despite the powerful effects of social context and social determinants embedded in political economy and sociolegal systems on the level and distribution of STDs, most of our research and surveillance attention focuses on the STDs themselves and to a limited extent on the individual behaviours associated with STD acquisition. It is important to develop standard techniques for summarising the extent and nature of sex work within populations and for determining the size and nature of the interactions among core groups, bridge populations, and the general population. Moreover, most research and surveillance activity tends to be conducted within local boundaries, without much attention to sexual links that relate many local sexual networks to each other. Given that prevalence of sex work seems dependent on global forces, and that sex workers seem to be highly mobile across geographic areas, it may be important to consider the establishment of surveillance systems that include monitoring of contextual parameters and social determinants at regional and global levels.³⁴ STD prevention programmes may be more effective if informed about the local, regional, and global context in which STD rates rise and fall; and which create the inequalities in STD incidence across societies and across groups defined by race-ethnicity and socioeconomic status.