Large variations exist between individual countries. In some African countries, the epidemic is still growing despite its severity. Others face a growing danger of explosive growth. The sharp rise in HIV prevalence among pregnant women in Cameroon (more than doubling to over 11% among those aged 20-24 between 1998 and 2000) shows how suddenly the epidemic can surge.
National HIV prevalence rates vary greatly between countries. In Somalia and Gambia the prevalence is under 2% of the adult population, whereas in South Africa and Zambia around 20% of the adult population is infected.
In four southern African countries, the national adult HIV prevalence rate has risen higher than was thought possible and now exceeds 24%. These countries are Botswana (37.3%), Lesotho (28.9%), Swaziland (38.8%) and Zimbabwe (24.6%).
West Africa is relatively less affected by HIV infection, but the prevalence rates in some countries are creeping up. In west and central Africa HIV prevalence is estimated to exceed 5% in several countries including Cameroon (6.9%), Central African Republic (13.5%), Côte d'Ivoire (7.0%) and Nigeria (5.4%).
Until recently the national prevalence rate has remained relatively low in Nigeria, the most populous country in sub-Saharan Africa. The rate has grown slowly from 1.9% in 1993 to 5.4% in 2003. But some states in Nigeria are already experiencing HIV prevalence rates as high as those now found in Cameroon. Already around 3.6 million Nigerians are estimated to be living with HIV.
HIV infection in Eastern Africa varies between adult prevalence rates of 2.7% in Eritrea to 8.8% in Tanzania. In Uganda the countrywide prevalence among the adult population is 4.1%.