**3.1. Routes of transmission, geographical and racial distribution**

In sub-Saharan Africa, the major route of transmission is through heterosexual contact rather than homosexual interaction. In an endemic country like Cameroon, for example, whereas at 2012, the HIV prevalent rate amongst adults was 4.3% (4.0%–4.6%), the infection is concen‐ trated within the 15–49 age bracket in which over 50% of the infected population are women [11]. The major mode of transmission identified by UNAIDS is largely heterosexual, with high occurrence amongst groups such as commercial sex workers, long distance truck drivers, injection drug users, and gay partners [12] with more than half of new HIV infection occurring through heterosexual activity [13]. The transmission of HIV infection is geographic as well as racial (as exemplified by cultural and social values) dependent (Figure 2). Differing factors has been adduced for infection rates in Africans, Asians, Americans, and Europeans which includes social values [14], economic stability/poverty [15, 16], level of awareness [17], and host genetic factors [18].

The three main established routes of transmission of the infection are sexual contact [19], blood transmission [20], needle sharing [21], and vertical (mother-to-child) [22] transmission. Heterosexual transmission seems to be the most common means of infection in Africa with over 60% of the global HIV infections [23] in contrast to other regions of the world, such as in USA which has homosexual transmission and needle sharing as the dominant means [19] (Figure 3). Sharing needles and injection instruments is thought to be three times more likely to transmit HIV than sexual intercourse.

The increased burden of HIV prevalence amongst women in endemic regions have been opined to be due to certain reproductive tract/biological susceptibility [24], social, physical, economical, and even psychological factors which women especially in sub-Saharan Africa are subjected to [25,26].

**Figure 2.** Estimated number of people (all ages) living with HIV based on 2013 WHO data

Available data shows that men who have sex with men (MSM) remain the group with the highest prevalence of HIV infection in the USA, accounting for up to 78% of total infection, as observed amongst men [27] (Figure 3). The prevalent rates amongst MSM are also recorded to increase in the order, Hispanic MSM (6,700), black MSM (10,600), and white MSC being the highest (11,200) [27]. Up to 16% of total HIV reported cases are due to intravenous drug users (IDUs) in which they represent 8% of new cases [28]. Similarly, Europe has a high number of HIV occurrences from MSM [29]. It could be observed that in high income countries HIV epidemics is highly associated with MEM sexual networks [30, 31,32] while heterosexual contacts prevail in low income regions [33,34,35] (Figure 3).

The data shows the prevalence based on 2013 United Nations Office on Drugs and Crime data from the annual report questionnaire and national Government reports, 2013 UNAIDS report and CDC publications. Note: IDUs stands for injecting drug users.

**Figure 3.** Regional distribution of HIV routes of transmission in HIV positive population
