Figure 1. Arms and recruitment patterns of Transmission Reduction Intervention Project (TRIP).

Drug injectors were referred to TRIP by collaborating testing sites. Based on the results of HIV and Limiting Antigen Avidity (LAg) testing, and on their testing history, drug injectors were grouped into the arms of the study: Recent Seeds, and Control Seeds with Long-term HIV infection. Control Seeds were matched to Recent Seeds for age (±5 years) and gender. The networks of Seeds were traced for two steps. The recruited network members underwent HIV, LAg, and viral load testing. Recents in networks were newly HIV-diagnosed network members of Seeds with documented testing history of recent infection in the last 6 months (last negative – first positive test < 6 months) irrespective of their LAg standardized Optical Density (ODn) value or had only LAg ODn ≤ 1.5 if testing history was unknown. Long-term infected participants in networks were those not classified as Recents.