Human immunodeficiency virus (HIV) causes HIV infection and AIDS. The virus attacks the immune system. When a person is infected with HIV, the virus slowly destroys the immune system. How fast this happens is different for each person. Treatment with a combination of medicines, called antiretroviral therapy (ART) can help slow or stop the destruction of the immune system.
CD4 Counts and the Immune System
Once the immune system is severely damaged, the person has AIDS and can now get infections and cancers that most healthy persons would not get.
Persons with AIDS usually have regular blood tests to check their CD4 cell count. CD4 cells are a type of T cell. T cells are one kind of cell of the immune system. They are also called "helper cells."
A normal CD4 count is from 500 to 1,500 cells/mm3 of blood. A CD4 cell count that is lower than normal may be a sign that the virus is damaging the immune system.
Doctors have found that when CD4 falls below certain counts, specific types of infections and cancers can develop. These illnesses are known as complications and are listed below.
Illnesses Common with a Lowered CD4 Count
BELOW 350 CELLS/mm3 of BLOOD
- Herpes simplex virus -- causes ulcers/small blisters in the mouth or genitals, happens more often and usually much more severely in an HIV-infected person than in someone without HIV infection.
- Herpes zoster (shingles) -- ulcers/small blisters over a patch of skin, caused by reactivation of the varicella zoster virus, the same virus that causes chickenpox.
- Kaposi's sarcoma -- cancer of the skin, lungs, and bowel due to a herpes virus (HHV-8). It can happen at any CD4 count, but is more likely to happen at lower CD4 counts, and is much more common in men than in women.
- Non-Hodgkin lymphoma -- cancer of the lymph nodes.
- Vaginal or oral thrush -- yeast (typically Candida albicans) infection of the mouth or vagina.
- Tuberculosis -- infection by tuberculosis bacteria mostly affects the lungs, but can also affect other organs such as the bowel, lining of the heart or lungs, brain, or lining of the central nervous system (brain and spinal cord).
BELOW 200 CELLS/mm3 of BLOOD
- Bacillary angiomatosis -- skin sores caused by a bacteria called Bartonella, which may be caused by cat scratches.
- Candida esophagitis -- painful yeast infection of the tube through which food travels, called the esophagus.
- Pneumocystis jiroveci pneumonia (PCP pneumonia) -- caused by a fungus.
BELOW 100 CELLS/mm3 of BLOOD
- AIDS dementia -- worsening and slowing of mental function, caused by HIV.
- Cryptococcal meningitis -- fungal infection of the lining of the brain.
- Cryptosporidium enteritis -- extreme diarrhea caused by a parasite that affects the gastrointestinal tract.
- Progressive multifocal leukoencephalopathy -- a disease of the brain caused by a virus (called the JC virus) that results in a severe decline in mental and physical functions.
- Toxoplasma encephalitis -- infection of the brain by a parasite, called Toxoplasma gondii, which is often found in cat feces; causes lesions (sores) in the brain.
- Wasting syndrome -- extreme weight loss and loss of appetite, caused by HIV itself.
BELOW 50 CELLS/mm3 of BLOOD
- Cytomegalovirus infection -- a viral infection that can affect almost any organ system, especially the large bowel and the eyes.
- Mycobacterium avium -- a blood infection by a bacterium related to tuberculosis.
Quinn TC. Epidemiology of human immunodeficiency virus infection and acquired immunodeficiency syndrome. In: Goldman L, Schafer AI, eds.Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 392.
Sterling TR, Chaisson RE. General clinical manifestations of human immunodeficiency virus infection (including the acute retroviral syndrome and oral, cutaneous, renal, ocular, metabolic, and cardiac diseases). In: Mandell GL, Bennett JE, Dolin R, eds.Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 7th ed. Philadelphia, PA: Elsevier Churchill Livingstone; 2009:chap 121.
Review Date 5/19/2013
Updated by: Jatin M. Vyas, MD, PhD, Assistant Professor in Medicine, Harvard Medical School; Assistant in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital. David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial team.