Syphilis and HIV in Sexual Networks of Men who have Sex with Men (MSM) in Los Angeles County, California

Background:
MSM online sex seeking creates sexual networks that facilitate dramatically higher syphilis and HIV rates than in other populations. Traditional venues such as bars also continue to thrive. These provide different sexual networks that also contribute to higher syphilis and HIV morbidity.

Objective:
To describe two types of venue-specific sexual networks that contribute to high syphilis and HIV morbidity in MSM and discuss implications of interventions.

Method:
A representative online network of a syphilis index case was compared to a representative bar syphilis case network using UCINet software. Demographic and partner data was extracted from data routinely collected as part of syphilis case investigation.

Result:
A syphilis patient with 63 partners met online led to a centralized network of 319 partners averaging 37.4 years old and 2 recent partners (range: 1-66). 9.1% had syphilis and/or HIV. But, 93% were directly exposed, and 100% had partners directly exposed to these diseases. The bar network began with a syphilis patient with 19 partners. It led to a denser centralized network of 123 averaging 24.3 years old, and 2 recent partners (range: 1-57). 3.1% had syphilis and/or HIV, but 50.9% were directly exposed and 100% had directly exposed partners. Both networks can be isolated into small groups incapable of spreading diseases by removing only 3 key members.

Conclusion:
The two networks are similar in demography and morbidity and centralization. Centralization is particularly apparent in the internet network, which can make it easier to interrupt. In contrast, the bar network has more contact between members and is more efficient at spreading infections as a result.

Implications:
More research on varied sexual networks will further our understanding of disease transmission, differential STD morbidity among MSM, and how to break chains of infections.