Donald E. Woodhouse

Social networks and infectious disease: The Colorado Springs study

The social network paradigm provides a set of concepts and methods useful for studying the structure of a population through which infectious agents transmitted during close personal contact spread, and an opportunity to develop improved disease control programs. The research discussed was a first attempt to use a social network approach to better understand factors affecting the transmission of a variety of pathogens, including hepatitis B virus (HBV) and human immunodeficiency viruses (HIV), in a population of prostitutes, injecting drug users (IDU) and their personal associates in a moderate-sized city (Colorado Springs, CO). Some of the challenges of studying large social networks in epidemiological research are described, some initial results reported and a new view of interconnections in an at risk population provided. Overall, for the first time in epidemiologic research a large number of individuals (over 600) were found connected to each other, directly or indirectly, using a network design. The average distance (along observed social relationships) between persons infected with HIV and susceptible persons was about three steps (3.1) in the core network region. All susceptibles in the core were within seven steps of HIV infection.

Social network dynamics and HIV transmission.

Objective:To prospectively study changes in the social networks of persons at presumably high risk for HIV in a community with low prevalence and little endogenous transmission. Methods:From a cohort of 595 persons at high risk (prostitutes, injecting drug users, and sexual partners of these persons) and nearly 6000 identified contacts, we examined the social networks of a subset of 96 persons who were interviewed once per year for 3 years. We assessed their network configuration, network stability, and changes in risk configuration and risk behavior using epidemiologic and social network analysis, and visualization techniques. Results:Some significant decrease in personal risk-taking was documented during the course of the study, particularly with regard to needle-sharing. The size and number of connected components (groups that are completely connected) declined. Microstructures (small subgroups of persons that interact intensely) were either not present, or declined appreciably during the period of observation. Conclusions:In this area of low prevalence, the lack of endogenous transmission of HIV may be related in part to the lack of a network structure that fosters active propagation, despite the continued presence of risky behaviors. Although the relative contribution of network structure and personal behavior cannot be ascertained from these data, the study suggests an important role for network configuration in the transmission dynamics of HIV.

Gonorrhea as a social disease

Gonococcal infection in Colorado Springs, Colorado, is concentrated in about 1% of the population. The social groups at risk are characterized as young, nonwhite, heterosexual, and connected to the military. They exhibit residential proximity by clustering in “core” census tracts; 51% of cases were in four tracts. They domonstrate residential stability and close social association at preferred sites for nighttime leisure activity (six major site out of 300 available). Social aggregation is further domonstrated by the length of social contract prior to sexual contact (45% had known each other for over two months). the neighborhood nature of sexual choices, and the grouping of sexually connected individuals in lots (six lots contained 20% of cases). The force of infectivity, measured in person-days of potential spread of gonorrhea by infected contacts, provides a quantitative assessment of the importance of identifiable social groups in the transmission of gonorrhea.

Mapping a social network of heterosexuals at high risk for HIV infection

Objective:To determine how heterosexuals at risk for HIV infection interconnect in social networks and how such relationships affect HIV transmission. Design:Cross-sectional study with face-to-face interviews to ascertain sociosexual connections; serologic testing. Participants:Prostitute women (n=133), their paying (n=129) and non-paying (n=47) male partners; injecting drug users (n= 200) and their sex partners (n=41). Participants were recruited in sexually transmitted disease and methadone clinics, an HIV-testing site, and through street outreach in Colorado Springs, Colorado, USA. Main outcome measures:Reported behaviors, risk perceptions, sociosexual linkages, and HIV prevalence. Results:Respondents were well informed, but reported engaging in high-risk behaviors frequently. Nevertheless, over 70% of respondents perceived themselves to be at low risk for HIV infection. The 595 respondents identified a social network of 5162 people to which they belonged. Network analytic methods indicated 147 separate connected components of this network; eight of the 19 HIV-positive individuals in the network were located in smaller components remote from the largest connected component. Conclusion:The isolated position of HIV-positive individuals may serve as a barrier to HIV transmission and may account for the lack of diffusion of HIV in heterosexual populations in this region. Network analysis appears useful for understanding the dynamics of disease transmission and warrants further development as a tool for intervention and control.

Risk network structure in the early epidemic phase of HIV transmission in Colorado Springs

This study describes the risk network structure of persons with HIV infection during its early epidemic phase in Colorado Springs, USA, using analysis of community-wide HIV/AIDS contact tracing records (sexual and injecting drug partners) from 1985 to 1999. Paired partner information from other STD/HIV programme records was used to augment network connections. Analyses were conducted with and without this supplemental information. The results suggest that a combined dendritic and cyclic structural network pattern is associated with low to moderate HIV propagation in Colorado Springs, and may account for the absence of intense propagation of the virus.

Choosing a centrality measure: Epidemiologic correlates in the Colorado Springs study of social networks☆

Abstract In a continuing analysis of a large network of persons who practice risky behaviors in an area of low prevalence for HIV transmission, we compared eight measures of centrality. Although these measures differ in their theoretical formulation and their distributional forms, they demonstrated substantial concordance in ranking as noncentral all but one of the HIV-positive persons in a large connected component of 341 persons, providing further support for the role of network structure in disease transmission.

Social and geographic distance in HIV risk.

Objective: The objective of this study was to examine the relationship between social distance (measured as the geodesic, or shortest distance, between 2 people in a connected network) and geographic distance (measured as the actual distance between them in kilometers [km]). Study: We used data from a study of 595 persons at risk for HIV and their sexual and drug-using partners (total N = 8920 unique individuals) conducted in Colorado Springs, Colorado, from 1988 to 1992—a longitudinal cohort study that ascertained sociodemographic, clinical, behavioral, and network information about participants. We used place of residence as the geographic marker and calculated distance between people grouped by various characteristics of interest. Results: Fifty-two percent of all dyads were separated by a distance of 4 km or less. The closest pairs were persons who both shared needles and had sexual contact (mean = 3.2 km), and HIV-positive persons and their contacts (mean = 2.9). The most distant pairs were prostitutes and their paying partners (mean = 6.1 km). In a connected subset of 348 respondents, almost half the persons were between 3 and 6 steps from each other in the social network and were separated by a distance of 2 to 8 km. Using block group centroids, the mean distance between all persons in Colorado Springs was 12.4 km compared with a mean distance of 5.4 km between all dyads in this study (P <0.0001). The subgroup of HIV-positive people and their contacts was drawn in real space on a map of Colorado Springs and revealed tight clustering of this group in the downtown area. Conclusion: The association of social and geographic distance in an urban group of people at risk for HIV provides demonstration of the importance of geographic clustering in the potential transmission of HIV. The proximity of persons connected within a network, but not necessarily known to each other, suggests that a high probability of partner selection from within the group may be an important factor in maintenance of HIV endemicity.

Psychiatric and Characterological Factors Relevant to Excess Mortality in a Long-Term Cohort of Prostitute Women

Abstract We previously reported on the causes of death in a 30-year open cohort of 1,969 prostitute women. Excess mortality was mostly accounted for by homicide, suicide, drug and alcohol toxicity, and AIDS, with AIDS deaths occurring in prostitutes identified as injecting drug users. Presently, we examine observed mortality trends in light of the literature on personality and psychopathological characteristics reported for prostitute women, and with reports linking such personality characteristics to excess mortality. We observed consistency between the observed pattern of mortality in prostitute women and mortality that would be expected in a sample of persons at high risk for antisocial and borderline personality disorder.

Aids in Colorado Springs: is there an epidemic?

ObjectiveTo analyze trends and patterns of HIV infection in a medium-sized community in the United States. MethodsSurveillance for AIDS and HIV infection was conducted by private physicians, military and public clinics, and blood and plasma donation centers. HIV-positive individuals were contacted and asked to refer their sex and injection partners for HIV-antibody testing. Prostitutes, injecting drug users and their sex partners were studied. Selected physicians were surveyed to assess under-reporting. ResultsThe 740 HIV-infected adults (67 with documented seroconversion) included 506 with no evidence of AIDS, 58 living with AIDS, and 1 76 who had died. Of the 126 patients cared for by local physicians, 107 (85%) had been reported. No major changes in behavioral risk factors or increases in the number of HIV-infected individuals occurred between 1986 (128) and 1992 (95). ConclusionsCharacteristics of individuals at risk and incidence of HIV infection have remained stable from 1981 to 1992. Analysis of data from the comprehensive surveillance and control program established in Colorado Springs in response to the AIDS epidemic suggests that, unlike the nations epicenters, HIV incidence in this location is neither widespread nor rapidly increasing. The age distribution of reported cases is slowly increasing, and the ratio of newly reported cases to deaths is declining, implying stable or decreasing incidence; deaths may soon exceed new cases. Using data routinely available to public health officials, we conclude that the epidemiologic picture of AIDS — like the clinical one —must be heterogenous, and that rational planning for the impact of AIDS should be based on the collection and analysis of local data.

Using knowledge of social networks to prevent human immunodeficiency virus infections : The Colorado Springs study

Abstract The development of an applied social science research project with implications for the management of infectious diseases is described. The project evolved out of a multidisciplinary effort to understand how sexually transmissible agents enter into social systems, are transmitted and can be identified, prevented and controlled. Collaborators began their investigations in the 1970s by looking at the social and behavioral patterns of individuals infected with gonorrhea, then applied similar methods in the late 1980s and early 1990s to examine the ways human immunodeficiency virus (HIV), the pathogen that causes AIDS, might spread among heterosexuals in a mid-sized American community. Concepts of personal and social networks of individuals linked by social, sexual and drug-sharing exposures guided the systematic collection of information from 595 participants in a large, prospective study. Results suggest that HIV did not spread among heterosexuals who engaged in risky sexual and needle-sharing beha...