Age related HIV incidence among sex workers

The result of the study below shows that the HIV incidence (rate of new HIV infection) among sex workers (the community with the highest HIV prevalence in Nigeria) is still low compared to countries like South Africa (with a HIV incidence as high as 5.0%). However, when you read the data shown in the abstract below, it is clear that the HIV incidence is highest in the age group 18 to 20 years in both the SAVVY and the CS3 trial. Is this a possible pointer to our target group among FSW in Nigeria?

Full paper can be accessed at
http://jech.bmj.com/content/early/2010/06/16/jech.2009.091959.short?q=w_jech_ahead_tab