**5.2. Global prevalence**

The prevalence of HIV serodiscordant infection in seronegative population has not been well documented. About 0.5 % (one in 200) people are reported in America [47]. Scott-Algara et al. [48] in 2003 reported that between 5 and 15 % of individuals of different populations at risk of HIV infection (regular partners of seropositive subjects, prostitutes and intravenous drug addicts) show no signs of apparent infection by HIV in spite of many years of exposure. However, some studies have indicated an estimate of about 5 % in Africa. Fowke et al. [49] in a cohort study showed that 4.3 % of HIV-1-exposed seronegative prostitutes in Kenya were persistently HIV negative after 12 years of follow-up study. Other reports have shown an increasing number of persistent serodiscordant-seronegatives and the risk of HIV transmission within stable serodiscordant partners across 23 countries of sub-Saharan Africa [50].

## **5.3. Classification of HIV natural resistance**

Those individuals who are serodiscordant-seronegative may possess natural resistance to HIV infection. They can be grouped into two: *highly exposed persistently seronegatives (HEPSs) and long-term nonprogressors (LTNPs)*
