November 29, 2015
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Human Immunodeficiency Virus (HIV) (cont.)

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What causes an HIV infection?

HIV is transmitted when infected material such as blood or semen or other infected fluids gains access to a new host. In the United States, surveillance statistics show there are approximately 1.1 million people living with HIV infection, but 18% are unaware that they are infected. Approximately 50,000 people get infected with HIV each year. Although the epidemic first was recognized in homosexual men, it has spread broadly throughout the U.S. New infections affect people from all subpopulations, although some groups are more likely to be affected than others. Of the 47,500 new infections in 2010, 63% were in men who had sex with men (MSN), 25% were acquired through heterosexual contact, and 8% were from injection drug use. HIV infection has hit the African-American community harder than other groups, with 44% of new infections occurring in this population, compared to 31% in whites and 21% in Hispanics. Over 600,000 Americans have died of HIV infection since the epidemic began.

Worldwide, there are approximately 34 million people living with HIV, and there are 2.5 million new cases each year. Since HIV infection was recognized, there have been 30 million deaths as a result of HIV infection.

What are the different stages of an HIV infection?

Untreated infection with HIV progresses over time and gradually impairs specific parts of the immune system, especially by destroying the white blood cells known as CD4 lymphocyte cells. This progression is described as occurring in stages. All stages require laboratory confirmation of HIV infection.

There are multiple different staging systems. For example, the Centers for Disease Control and Prevention case definition uses a staging system based on how much damage has been done to the immune system:

  • Stage 1 disease is the earliest phase. Stage 1 has no unusual infections or cancers or other conditions that would be associated with AIDS. In other words, stage 1 disease has no "AIDS-defining conditions" (see below). Although blood tests are positive for HIV, the CD4 cell count is at least 500 cells per microliter of blood (or >29% of all lymphocytes).
  • Stage 2 disease occurs when the CD4 count is between 200-499 cells per microliter (14%-28% of all lymphocytes), but again there are no AIDS-defining conditions present.
  • Stage 3 disease is synonymous with AIDS and is the most severe stage. There are two ways of diagnosing stage 3 disease: either by CD4 counts below 200 cells per microliter (<14% of lymphocytes) or through documentation of an AIDS-defining condition.

Another way to conceptualize HIV is according to the characteristics or clinical manifestations: acute infection, clinical latency, or AIDS.

  • Acute infection: Two to four weeks after infection with HIV, the patient can experience an acute illness, often described as "the worst flu ever." This is called acute retroviral syndrome (ARS) or primary HIV infection, and it is caused by the body's natural response to the HIV infection. Not all newly infected people develop ARS, however -- and it can take up to three months for it to appear. During this period of infection, large amounts of virus are being produced. The virus uses CD4 cells to replicate and destroys them in the process. Because of this, the CD4 count can fall rapidly. Eventually, the immune response will begin to bring the level of virus in the body back down to a level called a "viral set point," which is a relatively stable level of virus in the body. At this point, the CD4 count begins to increase, but it may not return to pre-infection levels. The human immune response suppresses the virus but does not eliminate it from the body.
  • Clinical latency: After the acute stage of HIV infection, the disease moves into a stage called clinical latency. This period is sometimes called asymptomatic HIV infection or chronic HIV infection. During this phase, HIV reproduces at very low levels, although it is still active. In this state, infected people may be able to maintain an undetectable viral load and a healthy CD4 cell count without the use of medication for a time. There are usually few if any symptoms. This period can last up to eight years or longer. However, some people progress through this phase faster than others. It is important to remember that people are still able to transmit HIV to others during this phase. Toward the middle and end of this period, the viral load begins to rise and the CD4 cell count begins to drop. As this happens, infected people may begin to have constitutional symptoms such as fatigue and other nonspecific symptoms.
  • AIDS: As the number of CD4 cells falls below 200 cells per cubic millimeter of blood (200 cells/cubic milliliter), people will be diagnosed as having AIDS. Normal CD4 counts are between 500 and 1,600 cells per cubic milliliter. This is the stage of infection that occurs when the immune system is badly damaged and patients become vulnerable to opportunistic infections. Without treatment, people who are diagnosed with AIDS typically survive about three years. Once someone has a dangerous opportunistic infection, life expectancy falls to about one year.

AIDS-defining conditions in an HIV-infected person include the following:

  • Candidiasis of bronchi, trachea, lungs, or esophagus
  • Cervical cancer, invasive
  • Disseminated or extrapulmonary coccidioidomycosis or Cryptococcus
  • Chronic intestinal cryptosporidiosis or isosporiasis
  • Cytomegalovirus disease of the retina or an unusual site (other than liver, spleen, or nodes)
  • HIV encephalopathy
  • Herpes simplex that does not heal or that occurs in the lungs or esophagus
  • Histoplasmosis that is disseminated or extrapulmonary
  • Kaposi's sarcoma
  • Lymphoid interstitial pneumonia and/or pulmonary lymphoid hyperplasia*
  • Selected lymphomas including Burkitt's, immunoblastic, or arising in the brain
  • Disseminated or extrapulmonary Mycobacterium avium-intracellulare complex or Mycobacterium kansasii, or other species of mycobacterium
  • Mycobacterium tuberculosis infection
  • Pneumocystis jirovecii pneumonia
  • Recurrent bacterial pneumonia
  • Progressive multifocal leukoencephalopathy
  • Recurrent or multiple bacterial infections
  • Recurrent Salmonella septicemia
  • Toxoplasmosis of brain
  • Wasting syndrome associated with HIV infection
Medically Reviewed by a Doctor on 3/3/2014


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