Date of Award


Degree Type


Degree Name

Master of Science in Pharmaceutical Sciences


Biomedical and Pharmaceutical Sciences

First Advisor

Ashley Buchanan


Background: People who inject drugs (PWID) are a well-identified risk population for HIV infection. The risk networks of PWID have been implicated as possible modulators of both HIV risk and educational interventions among this population. In order to further understand the nature of risk networks, we examined how individual characteristics were associated with influential network position based on high closeness, betweenness, or eigenvector network centrality. These centrality measures assess an individual’s importance or potential to influence others based on their connections, closeness is based on proximity to others, betweenness on acting as an intermediary between others, and eigenvector on connection to highly connected peers.

Methods: Using data from Athens, Greece collected as part of the Transmission Reduction Intervention Project (TRIP), we constructed a risk network and identified individuals in the top quartile of the distribution for each centrality measure. Using logistic regression, we identified associations between being in the top quartile of each centrality measure and individual characteristics such as demographics, risk behaviors, and altruistic behaviors. We also performed a series of sensitivity analyses to evaluate robustness of the results to the definition of high centrality (e.g., the top 50%, 20%, and 10% of the distribution of the centrality measure).

Results: The TRIP study contained a total 356 individuals after restriction to the largest connected component and censoring of individuals with missing covariate information a sample of 231 PWID was extracted from the TRIP study population. Individuals who injected at least once per day were more likely to have high closeness (odds ratio (OR) = 3.36; 95% confidence interval (CI) = 1.57, 8.42), betweenness (OR = 2.22 95% CI = 1.06, 4.67), or eigenvector centrality (OR = 4.50 95% CI = 1.89, 10.68). Individuals who engaged in sex without a condom were less likely to have high closeness centrality (OR = 0.18 95% CI =0.07, 0.45) or high eigenvector centrality (OR = 0.19 95% CI =0.07, 0.49). Individuals who reported higher numbers of sex partners were more likely to have high betweenness centrality (OR = 1.04 95% CI =1.00, 1.08). Years living in the project recruitment area was also associated with high eigenvector centrality (OR = 1.04 95% CI = 1.00, 1.09).

Conclusions: Injection frequency was consistently related with network position and likely indicates that individuals who inject more frequently have more interactions with other PWID. Unprotected sex was also related to network centrality and may reflect that less central individuals may have less exposure to public health outreach about risk reduction, including condom use. Work to identify how individual characteristics relate to the underlying structure of PWID risk networks may provide insight into how to improve public health responses to future HIV outbreaks by identifying people of interest, who make be integral to possible transmission routes or who may be missed by standard outreach approaches.

Available for download on Saturday, August 14, 2021