Table 1 Group information

Standard of care arm

1. Information card: the risk of acquiring syphilis, the importance of screening for syphilis, resources of three local syphilis test and linkage to care service sites, and a link of national syphilis VCT sites.

2. Peer notification card: social network distribution of notification card and encouragement of syphilis testing.

3. Result report card

1. Each index will receive 3 information packages at enrollment, and distribute packages to 3 alters. Maximum ONE package per alter.

2. Each alter who returns his testing result and completes a survey can receive 3 USD and his matched index will also receive an extra 3 USD.

3. Each index can apply for additional 3 packages when all his 3 alters return testing results.

4. Each eligible “secondary index” can apply for 3 information packages to distribute to his alters.

Standard SST delivery arm

1. Information card: the risk of acquiring syphilis, the importance of screening for syphilis, resources of three local syphilis test and linkage to care service sites, and a link of national syphilis VCT sites.

2. SST kit package: social network distribution of SST kit package and encouragement of SST.

3. Result report card

1. Each index will receive 3 SST packages at enrollment, and distribute packages to 3 alters. Maximum ONE package per alter.

2. Each alter who returns his testing result and completes a survey can receive 3 USD and his matched index will also receive an extra 3 USD.

3. Each index can apply for additional 3 packages (refundable deposit 3 USD/package) when all his 3 alters return testing results.

4. Each eligible “secondary index” can apply for 3 SST packages (refundable deposit 3 USD/package) to distribute to his alters.

Referral link SST delivery arm

1. Information card: the risk of acquiring syphilis, the importance of screening for syphilis, resources of three local syphilis test and linkage to care service sites, and a link of national syphilis VCT sites.

2. SST referral link: social network distribution of SST referral links and encouragement of SST.

3. Result report card

1. Each index will receive 3 SST referral links at enrollment, and distribute links to 3 alters. Maximum ONE link per alter.

2. Each alter can apply for ONE SST package through the referral link, and SST package will be posted to him free of charge.

3. Each alter who returns his testing result and completes a survey can receive 3 USD and his matched index will also receive an extra 3 USD.

4. Each index can apply for additional 3 referral links when all his 3 alters return testing results.

5. Each eligible “secondary index” can apply for 3 SST referral links to distribute to his alters.