**3.2. Exploring transmission models**

Since both heterosexual and homosexual behaviour is a potent factor for increased HIV transmission rate, exploring the dynamics of this mode perhaps could be a sure way of providing and discovering a lasting HIV treatment option and drug design. A number of HIV epidemic models have emerged, particularly the modes of transmission (MOT) model recommended by the Joint United Nations Programme on HIV/AIDS (UNAIDS) [36,37]. The MOT model as developed in 2002 aims to identify persons at risk of HIV infection [38] with subsequent prevention policies and programmes [39]. This model was recommended for country-wide studies in the year 2008 as part of a synthesis process supported by UNAIDS and the World Bank Global HIV/AIDS Monitoring and Evaluation Team [40], with emphasis on local content and immediate environment prevailing circumstances. The MOT model utilizes accurate information on recent prevalence of HIV infections in a given population and the assumed patterns of risk behaviour within different risk groups (MSM, prostitutes, etc.) to calculate the expected distribution of new adult HIV infections the next year in terms of the mode of exposure. Certain considerations are necessary for a comprehensive and adequate utilization of this model either at country or community level studies. These considerations as noted by WHO are the proportion of the adult male and female population that belongs to each of several risk groups identified, such as commercial sex workers and their patronizers, injection drug users, men who sex men (MSM), persons of multiple heterosexual sex partners, the low risk group such as partners of persons with higher-risk behaviour and married or cohabiting couples with one monogamous heterosexual partner in the last year [41]. The model tends to resolve issues such as complexity in risk groups, for example, a prostitute who is a drug injection user. Secondly, the prevalent rate of HIV infection and of a generic sexually transmitted disease (STI) identified in each risk group [41]. Thirdly, the average numbers of sexual or injecting partners and exposures per partner with considerations of personal level protective behaviour (such as condom use or the use of new needles), for individuals in each risk group and lastly the probability of HIV transmission per exposure act in each risk group, taking into account the effect of STIs and the prevalence of male circumcision [41].
