Sex, drugs, and race: how behaviors differentially contribute to the sexually transmitted infection risk network structure

Abstract

Objectives: We examined how risk behaviors differentially connect a population at high risk for sexually transmitted infections.

Methods: Starting from observed networks representing the full risk network and the risk network among respondents only, we constructed a series of edge-deleted counterfactual networks that selectively remove sex ties, drug ties, and ties involving both sex and drugs and a comparison random set. With these edge-deleted networks, we have demonstrated how each tie type differentially contributes to the connectivity of the observed networks on a series of standard network connectivity measures (component and bicomponent size, distance, and transitivity ratio) and the observed network racial segregation.

Results: Sex ties are unique from the other tie types in the network, providing wider reach in the network in relatively nonredundant ways. In this population, sex ties are more likely to bridge races than are other tie types.

Conclusions: Interventions derived from only 1 mode of transmission at a time (e.g., condom promotion or needle exchange) would have different potential for curtailing sexually transmitted infection spread through the population than would attempts that simultaneously address all risk-relevant behaviors.

FIGURE 1—

Ties among (a) the giant connected component for the full network, and (b) the observed respondent-only network: Colorado Springs Project 90, Colorado Springs, CO, 1988–1992. Note. The full network includes 4319 people (of 6019 total named) and the 13 901 ties between them. The respondent-only network consists of 595 respondents and the 1296 reported connections between them.

FIGURE 2—

Changes for the simulated counterfactual full network with the indicated percentage of all edges removed as sex ties, drug ties, ties involving sex and drugs, or random ties for (a) largest component size, (b) relative size of largest bicomponent, (c) relative average distance, and (d) transitivity ratio: Colorado Springs Project 90, Colorado Springs, CO, 1988–1992. Note. All differences are significantly different (P<.01).

FIGURE 3—

Changes for the simulated counterfactual participant-only network with the indicated percentage of all edges removed as sex ties, drug ties, ties involving sex and drugs, or random ties for (a) largest component size, (b) relative size of largest bicomponent, (c) relative average distance, and (d) transitivity ratio: Colorado Springs Project 90, Colorado Springs, CO, 1988–1992. Note. All differences are significantly different (P<.01).

FIGURE 4—

Racial/ethnic segregation for respective levels of edge deletion in the full network, and the network consisting only of P90 respondents: Colorado Springs Project 90, Colorado Springs, CO, 1988–1992.