Table 1.

Definition of men who have sex with men (MSM) at risk, or not at risk of HIV acquisition or transmission, based on the theory of the 2015 Break the Chains campaign, Switzerland, March–May 2015

MSM with specified HIV risks (MSMwr)*	MSM with no specified HIV risks (MSMnr)*
CAI with a partner of unknown or different HIV status (steady and/or casual partners) over the last 12 months	Did not report any of the criteria for MSMwr; considered to have avoided any risk of HIV transmission†
CAI with casual partners over the last 12 months
Unknown HIV status within a steady partnership over the last 12 months
HIV negative with steady partner who is HIV positive but does not receive antiretroviral therapy and/or has a detectable viral load
HIV positive with detectable viral load‡

*MSMwr and MSMnr are mutually exclusive categories.

†MSM in this category are assumed to continue to avoid any risk of HIV transmission during the campaign and follow-up period.

‡MSM with HIV infection and a detectable viral load are at risk of transmitting HIV. They were not included in the calculation of those adopting the campaign message because they would not be expected to have another HIV test.

CAI, condomless anal intercourse.