It is the capitol of the richest nation on earth, yet Washington, DC has one of the highest HIV infection rates in the world - 3.2 per cent higher than Rwanda, Kenya or Ethiopia. The problem is worst in Anacostia. The mostly black neighbourhood is beset by low education and high unemployment. Ex-felon, Dwayne Williams once ran these streets as a drug dealer. Now, he drives them... in a mobile testing lab. Al Jazeera's Kimberly Halkett reports