Acquired immunodeficiency syndrome, called AIDS, is the advanced stage of infection caused by the human immunodeficiency virus or HIV, which over time destroys the immune system.


As soon as HIV enters the body, it begins to disable or destroy these cells, often without causing symptoms. Even if you don’t experience HIV symptoms, the virus is actively multiplying, infecting and killing cells of the immune system — CD4+T cells, which are the immune system’s key infection fighters.

HIV can be spread by:

  • Blood transfusions with HIV-infected blood. This is rare since all donated blood is tested for HIV.
  • HIV-contaminated needles.
  • Sexual contact, especially intercourse or anal sex.
  • A mother to child during pregnancy, childbirth or breastfeeding.

Sexually transmitted diseases such as syphilis, genital herpes, chlamydia or gonorrhea appear to increase the susceptibility of getting HIV during sex with infected partners.

In rare instances, HIV can be spread by:

  • A bite by someone infected with HIV.
  • Blood from an HIV-infected person entering an open wound.
  • Sharing personal hygiene items, such as razors and toothbrushes, with a person infected with HIV.

HIV is not spread through casual contact such as sharing food, utensils, towels, bedding, swimming pools, telephones or toilet seats. HIV also is not spread by insects, such as mosquitoes or bedbugs.

Many people don’t have any symptoms when they first become infected with HIV. Some have a flu-like illness, called HIV sero-conversion syndrome, a month or two after exposure to the virus. This illness may cause a variety of symptoms including:

  • Diarrhea
  • Enlarged liver or spleen
  • Fever
  • Enlarged or swollen lymph nodes
  • Headache
  • Muscle pain
  • Nausea and vomiting
  • Neurologic symptoms
  • Rash on the abdomen, arms and legs and face
  • Sore throat
  • Thrush, a common fungal infection of the mouth caused by Candida, a yeast-like fungus

These symptoms usually disappear in a week to a month and may be mistaken for other viral infections. During this period, people are very infectious and HIV is present in large quantities in genital fluids.

An infected person may not experience severe symptoms for eight to 10 years or more. This period — called the asymptomatic period — varies in length for each person. Some people may have symptoms within a few months and others may be symptom-free for years.

Children born with HIV usually have symptoms within two years of birth. Children may grow slowly or become sick frequently.

As the immune system weakens, other complications may occur. For many people, the first signs of infection are large lymph nodes or swollen glands that may be enlarged for more than three months. Other symptoms before the onset of AIDS include:

  • Fevers and sweats
  • Herpes infections that cause severe mouth, genital or anal sores
  • Lack of energy
  • Pelvic inflammatory disease in women that does not respond to treatment
  • Persistent skin rashes or flaky skin
  • Shingles, a painful nerve disease often accompanied by a rash or blisters
  • Short-term memory loss
  • Weight loss


AIDS is the advanced stage of HIV infection, when the immune system is damaged. Without treatment, about half of those with HIV develop AIDS within 10 years, although the period between infection and development varies widely from one to 20 years.

Symptoms are caused by the deterioration of the immune system and the decline of CD4+ T cells that are the immune system’s key infection fighters. As soon as HIV enters the body, it begins to destroy these cells.

Some common symptoms include:

  • Diarrhea that lasts for more than a week
  • Dry cough
  • Memory loss, depression and neurological disorders
  • Pneumonia
  • Profound, unexplained fatigue
  • Rapid weight loss
  • Recurring fever or profuse night sweats
  • Red, brown, pink or purplish blotches on or under the skin or inside the mouth, nose or eyelids
  • Swollen lymph glands in the armpits, groin or neck
  • White spots or unusual blemishes on the tongue, in the mouth, or in the throat

People with AIDS have difficulty fighting infections caused by viruses, bacteria, fungi and parasites and often die from opportunistic infections, rather than from AIDS itself. Symptoms of opportunistic infections common with AIDS include:

  • Coma
  • Coughing and shortness of breath
  • Difficult or painful swallowing
  • Extreme fatigue
  • Fever
  • Mental symptoms such as confusion and forgetfulness
  • Nausea, abdominal cramps and vomiting
  • Seizures and lack of coordination
  • Severe, persistent diarrhea
  • Severe headaches
  • Vision loss
  • Weight loss

AIDS is now a pandemic. In 2007, it was estimated that 33.2 million people lived with the disease worldwide, and that AIDS killed an estimated 2.1 million people, including 330,000 children.

Although treatments for AIDS and HIV can slow the course of the disease, there is no known cure or vaccine. Antiretroviral treatment reduces both the mortality and the morbidity of HIV infection, but these drugs are expensive and require routine access to them.

Due to the difficulty in treating HIV infection, preventing infection is a key aim in controlling the AIDS pandemic. Health organizations promote safe sex and needle-exchange programs in attempts to slow the spread of the virus.