Dear Dr, If a person exposed to HIV and does not have any medical treatment, how long his CD+ will decease to 300? I read a article and said CD+ will decrease average 70~100 each year. Is it right?

The rate of CD4+ decline for people living with HIV is quite variable. If you read about an "average decline" it would have to be based on data for a group of people. An average is a statistical number that takes into account the range for the people in the group and where the majority of people fall within the statistical curve. The problem is you can't then apply that to a given individual. Some people have little or no decline in their CD4+ cells for 20 years or more (without therapy) and others can show a rapid decline (e.g. several hundred) within a year. Most people are somewhere in between.

The most important thing is for a person living with HIV to see a doctor regularly and for them to follow the patterns of change in their own immune functioning. This includes CD4+ cells and several other markers of immune functioning. Knowing one's own pattern and rate of change is key to making treatment decisions.