Table 1. Definitions (listed in alphabetical order within each category).

General Definitions
Acute infection	The initial phase of HIV infection before developing antibodies.
LAg	⦁ Limiting Antigen Avidity Assay is a blood test based on antibody maturation that helps detect people with recent HIV infection.
	⦁ If the LAg-based standardized Optical Density (ODn) score of a biological sample is ≤ 1.5, the sample has probably been collected from a person who acquired HIV in the past 6 months.
Long-term infection (Long-standing infection)	An HIV infection that occurred more than 6 months ago.
Long-term infected person	A person who acquired HIV more than 6 months ago.
Partner Notification and Counseling Services (PNCS)	A broad array of services to people diagnosed with HIV that include partner notification, prevention counseling, testing for HIV and other sexually transmitted infections, and provision of and/or linkage to medical and/or psychosocial services.
Recent infection	An HIV infection that occurred in the previous 6 months.
Recently infected person (Recent infectee)	A person who acquired HIV in the previous 6 months.
Recency	The first 6 months of HIV infection.
Social Network Contact Tracing	An extension of partner-based services that recruits network members (sexual or injecting partners, friends, acquaintances) of HIV infected people.
TRIP	⦁ Transmission Reduction Intervention Project.
	⦁ A social network contact tracing intervention that is based on recently infected HIV+ individuals.
	⦁ It is based on the concept that recruiting and testing network members of recent infectees is likely to identify more people who are recently infected or highly infectious and are thus more likely to pass the infection on to others.
	⦁ It takes actions to reduce transmission such as educating people about recent infection, distributing alerts within recents’ networks about the presence of highly-infectious individuals (targeting also the untested fraction of networks) and linking infected clients to care and antiretroviral treatment.
Operational Definitions
Borderline Recent	⦁ A person detected in networks of Recent or Long-term Control Seeds who marginally failed to meet the operational definition of Recent in network (see below) but was treated as Recent in terms of network contact tracing (a two-step recruitment process follows).
	⦁ He/she was a newly HIV-diagnosed person with documented or very reliable self-reported testing history of infection in the last 9 months (last negative – first positive test < 9 months) irrespective of his/her LAg ODn value or he/she had unknown testing history but very high viral load typical of recent infection (>100,000 or 5 log10 copies/ml) irrespective of his/her LAg ODn value.
Control Seed with Long-term HIV infection (LCS)	⦁ A newly HIV-diagnosed but probably not recently infected drug injector who was referred from collaborating testing facilities and who had LAg ODn >1.5 without any evidence of seroconversion in the last 6 months.
	⦁ LCSs and their network members comprised a control arm.
	⦁ LCSs were matched to Recent Seeds for age (±5 years) and gender.
	⦁ Many LCSs first learned about their infection at around the time of their TRIP baseline interview.
	⦁ LCSs were asked to elicit names of and help recruit and test members of their social networks.
	⦁ Network recruitment for LCS stopped at second degree network members unless a Recent or a Borderline Recent was identified; then a new two-step recruitment process began.
Recent Seed (RS)	⦁ A newly HIV-diagnosed and probably recently infected drug injector referred from collaborating testing facilities who had documented seroconversion in the previous 6 months (last negative – first positive test < 6 months) and LAg ODn ≤1.5 or had only LAg ODn ≤1.5 if testing history was unknown.
	⦁ RSs and their network members comprised the Intervention Arm.
	⦁ RSs were asked to elicit names of and help recruit and test members of their networks.
	⦁ Network recruitment for RS stopped at second degree network members unless a Recent or a Borderline Recent was identified; then a new two-step recruitment process began.
Recent	⦁ A person detected in networks of Recent or Long-term Control Seeds who is probably recently infected with HIV.
	⦁ He/She is a newly HIV-diagnosed network member with documented testing history of recent infection (last negative – first positive test < 6 months) irrespective of his/her LAg ODn value or with only LAg ODn ≤1.5 if testing history was unknown.
	⦁ The term includes acutely infected persons in TRIP i.e. network members whose samples were antibody negative but tested HIV RNA positive in pools of 10.
Seed	⦁ Primary participant (drug injector) recruited by TRIP who had been tested and found HIV positive by collaborating testing and counseling facilities.
	⦁ Seeds’s specimens underwent LAg testing in TRIP.
	⦁ Seeds were asked to elicit names of and help recruit and test members of their networks.
	⦁ Network recruitment for Seeds stopped at second degree network members unless a Recent or a Borderline Recent was identified; then a new two-step recruitment process began.
Definitions of Metrics
Network Contact Tracing Yield (NCTY)	⦁ It is calculated by dividing the number of Recents/Borderline Recents identified in Seeds’ networks by the initial number of people who were enrolled as Seeds.
	⦁ It represents the ability to detect Recents/Borderline Recents in networks of people who are used as Seeds for recruitment.
Proportion of Recents in Network (PRN)	⦁ It is calculated by dividing the number of Recents/Borderline Recents identified in Seeds’ networks by the size of these networks.
	⦁ It represents the prevalence of Recents within networks.
Proportion of Recents among Positives in Network (PRPN)	⦁ It is calculated by dividing the number of Recents/Borderline Recents identified in Seeds’ networks by the total number of HIV positives identified in these networks.
	⦁ It is the prevalence of Recents/Borderline Recents among the positives in networks of Seeds.
Recents Incidence in Network (RIN)	⦁ It is calculated by dividing the number of Recents/Borderline Recents identified in Seed’s networks by the total number of Recents and HIV negatives in these networks.
	⦁ It is a proxy for HIV incidence in networks.