Jean Vandepitte, MD, et. al., in the June 2006 Sexually Transmitted Infections article "Estimates of the Number of Female Sex Workers in Different Regions of the World," wrote:

“In sub-Saharan Africa, the FSW [Female Sex Workers] prevalence [percent equals estimated number of FSW in an area multiplied by 100 and divided by the size of an area’s female population between the ages of 15-49] in the capitals ranged between 0.7% and 4.3% and in other urban areas between 0.4% and 4.3%. Population surveys from this same region yielded even higher proportions of women involved in transactional sex. The national FSW prevalence in Asia ranged between 0.2% and 2.6%; in the ex-Russian Federation between 0.1% and 1.5%; in East Europe between 0.4% and 1.4%; in West Europe between 0.1% and 1.4%; and in Latin America between 0.2% and 7.4%…

[M]ost countries in the world do not know the size of this population group. The estimates of the prevalence of FSW presented in this paper show how important this hard-to-reach population group is in all parts of the world.”

June 2006