A nonlinear model is developed for an epidemic with contact tracmg, and its dynamic is studied. A linear version of the model is presented in both deterministic and stochastic versions. We present the data for the cuban HIVIAIDS epidemic and fit the linear model to the data, we obtain estimates for the size of the Cuban HIV epidemic.

Vietnam's HIV epidemic is increasing predominantly and most rapidly among IDUs. However, prevalence rates among FSWs and STD patients are rising but are still low among pregnant women and army conscripts. Vietnam, at present, is still in the early phase of the HIV epidemic and has time to take effective and appropriate actions.