Table 1.

Definitions used in the model to classify individuals according to risk behaviour

Risk group	Definition
High risk populations	Individuals who are IDUs, MSM or FSWs
Most at risk network	Individuals who engage in a risk network of IDUs, MSM or FSWs and their clients
Individuals engaging in casual heterosexual sex (intermediate risk group)	Individuals who have had more than one sexual partner in the last year
Partners of IDUs, partners of clients of FSWs, female partners of MSM, partners of individuals engaging in casual heterosexual sex	Individuals who have had one sexual partner in the last year and whose partners are allocated to the IDUs, clients of FSWs, MSM or casual heterosexual sex risk groups
Individuals engaging in low-risk heterosexual sex	Individuals who have had one heterosexual sex partner in the last year and their partners have also had only one heterosexual sex partner in the last year. This group consists of individuals in monogamous partnerships who are faithful to their partners and their partners are faithful to them, and their partners are neither IDUs nor men MSM
Individuals at no risk	Individuals who have had no sexual partners in the last year. This may be a result of primary abstinence (never had sexual intercourse) or secondary abstinence (had sexual intercourse in the past but not currently sexually active)

IDU, injecting drug user; MSM, men who have sex with men; FSW, female sex worker