After a person is infected with hiv, the number of CD4 cells goes down. A normal count is 600 to 1500 per cubic milliliter of blood when the count drops below 200. the body's immune system cannot work well at all With a cd4 count below 200, a simple infection could cause a lot of trouble because the body cannot fight it off.After a person is infected with HIV, the number of CD4 cells goes down. A normal count is 600 to 1500 per cubic milliliter of blood. When the count drops below 200, the body’s immune system cannot work well at all. With a CD4 count below 200, a simple infection could cause a lot of trouble because the body cannot fight it off