Background:
The Internet has emerged as a venue that facilitates sexual partnering. In Autumn 2005, community physicians reported the first cases of HIV and syphilis occurring among residents of a North Side Chicago apartment building.

Objective:
To determine the extent of the outbreak, and to identify public health interventions to limit further disease transmission in the community.

Method:
Data were obtained from reported syphilis and HIV case records, patient interviews, and medical chart reviews. Cases, contacts, and associates were linked to identify the sexual network. Epidemiologic Visual Case Analysis and cluster analysis were performed.

Result:
Investigation revealed a dense sexual network of 47 persons and documented syphilis and HIV infections associated with an Internet pornography business operated out of a residential apartment building. Exposure histories and incubation periods were consistent with transmission of syphilis and HIV within the sexual network. Of the 19 individuals who were identified as employees of the business, the median age was 23 years (age range 19-35) and all were African-American males. Of the 19 men involved with the business, nine (47%) were infected with HIV, and nine (47%) were with syphilis. Six (32%) men were co-infected with syphilis and HIV. In total, 10 cases of syphilis and 13 cases of HIV infection were identified in this large sexual network.

Conclusion:
A large cluster of syphilis and HIV infections was identified among a sexual network associated with an Internet pornography website.

Implications:
Public Health Departments need to develop effective program and policy responses to the changing role of the Internet in STD/HIV disease transmission.