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Spatial Bridges and the Spread of Chlamydia: The Case of a County in Sweden

Nordvik, Monica K. BA*; Liljeros, Fredrik PhD*; Österlund, Anders MD, PhD, MPH†‡; Herrmann, BjÖrn PhD§

Sexually Transmitted Diseases: January 2007 - Volume 34 - Issue 1 - p 47-53
doi: 10.1097/01.olq.0000222722.79996.4b

Objectives: The so-called small-world effect can have a great impact on efforts to control the incidence and prevalence of sexually transmitted infections. This is because a small number of so-called spatial bridgers (individuals who, through sexual contacts, interconnect geographically distant areas) can drastically lower the average path length in the sexual network and, as a result, make locally based intervention programs much less effective. The objectives of this study were to analyze the sociodemographic characteristics of these bridgers and to compare the result with the remaining study population. The purpose was to determine whether it is possible to identify them for targeted intervention programs.

Study Design: During 2001, contact tracing was performed in approximately 98% of all cases with positive test results in Värmland County. The sexual networks obtained constituted a study population of 851 individuals. Statistical analysis was used to characterize individuals engaged in spatial bridging behavior.

Results: Approximately 8% of the study population was characterized as spatial bridgers. Using multivariate analysis, we found almost no significant differences between these individuals and the rest of the study population when it came to sociodemographic variables, including education, economy, and ethnicity.

Conclusion: The number of spatial bridgers is high enough to create a small-world network with links that can fuel the endemic chlamydia in Värmland County. Sociodemographic information could not be used to characterize spatial bridgers. In interventions against chlamydia, spatial bridgers shall be considered as potentially important for sustaining the disease.

An analysis of contact tracing data from a Swedish county found no significant differences in sociodemographic characteristics between sexual spatial bridgers and nonbridgers.

From the *Department of Sociology, Stockholm University, Stockholm, Sweden; the †Department of Communicable Disease Control and Prevention, Central Hospital, Karlstad, Sweden; presently the ‡Department of Communicable Disease Control and Prevention, Landstingshuset, Luleå, Sweden; and the §Section of Clinical Microbiology, Uppsala University Hospital, Uppsala, Sweden

The authors thank Ingrid Persson and Tina Persson, Department of Communicable Disease Control and Prevention, Central Hospital, Karlstad for the data search and Torsten Berglund, Devon Brewer, and Alden Klovdahl for comments.

This work has been supported by the National Institute of Public Health (NIPH) in Sweden and the European research NEST project DYSONET 012911.

Correspondence: Monica K. Nordvik, Department of Sociology, Stockholm University, S-106 91, Stockholm, Sweden. E-mail:

Received for publication January 19, 2006, and accepted April 6, 2006.

© Copyright 2007 American Sexually Transmitted Diseases Association