Areas of the body (other than blood) where HIV may establish itself such as in lymph nodes, gut-associated lymphoid tissue (in the intestines), cerebral spinal fluid (CSF) and the brain. HIV drugs cannot reach these areas well, although some penetration does occur, but it is limited compared to drug concentration in blood. HIV antiretroviral treatment is best reducing the (circulating) blood viral load where many of the HIV target immune cells also circulate. This is another reason early HIV antiretroviral treatment is recommended (especially during acute and primary infection) before HIV has much chance at entering the viral reservoirs. It is also why early diagnosis (through HIV testing) is important so that treatment can commence before HIV has progressed throughout the body’s viral reservoirs where treatment can less penetrate.