Human Immunodeficiency (HIV)

There are two major types of HIV, type 1 (HIV-1) and type 2 (HIV-2). HIV-1 viruses are further divided into groups M, N, O, P. Group M viruses are the most common group and are predominately responsible for the AIDS pandemic. Group M is further subdivided into clades based on their genetic sequences, which tend to concentrate within specific geographic regions. The clade that an individual becomes infected with can be a major factor in the rate of progression to AIDS; specifically clades C, D and G are 8 times more likely to develop AIDS.

HIV-2 is mostly found in West Africa and it is also divided into groups (A to H). It is less easily transmitted than HIV-1 and the time between infection and symptoms tends to be longer. Despite its relative geographic confinement, HIV-2 should be considered in all patients exhibiting symptoms of HIV.

HIV is divided into three main stages:

Acute Retroviral Syndrome: Early symptoms of HIV are defined as acute retroviral syndrome and they appear 3-6 weeks after infection and can easily be confused with the symptoms of the flu or other milder diseases. As a result, most infections remain undiagnosed until they progress to more advanced stages.

Clinical Latency (inactivity or dormancy): This period is sometimes called asymptomatic HIV infection or chronic HIV infection. During this phase HIV is active but reproduces at very low levels. People who are on antiretroviral therapy may live with clinical latency for several decades. Toward the middle and end of this period, the viral load begins to rise and the CD4+ cell count begins to drop. The World Health Organization (WHO) sub-classifies this period into three stages based on the CD4+ cell count of the individual:

STAGE 1: the CD4+ cell count is at least 500 cells per microliter

STAGE 2: the CD4+ cell count is 350 to 499

STAGE 3 (advanced HIV disease, or AHD): The CD4+ cell count is 200 to 349

AIDS (Acquired Immunodeficiency Syndrome): This is the stage of infection that occurs when the immune system is badly damaged and an infected individual become vulnerable to opportunistic illnesses. The CD4+ cell count is less than 200 or the percent of CD4+ cells is less than 15% of all lymphocytes. Without treatment, people who are diagnosed with AIDS typically survive about 3 years. Once a dangerous opportunistic illness is acquired, life expectancy without treatment falls to about 1 year.