What is HIV?

Reviewed by: HU Medical Review Board | Last reviewed: September 2019

HIV (human immunodeficiency virus) is a virus that lives in the blood and infects CD4 cells in the body. CD4 cells are also referred to as T cells and are important cells in the immune system that help our bodies fight off infection.1 As HIV progresses, the number of CD4 cells within the body decreases. The lower the number of CD4 cells (also called a CD4 count), the more susceptible an individual is to serious and life-threatening illnesses, including infections and certain cancers.

If HIV is not treated and continues to progress, it may lead to AIDS (acquired immunodeficiency syndrome) in anywhere from two to twenty years. AIDS is defined as having a CD4 count of less than 200 or one of the many AIDS-defining illness, like invasive cervical cancer, or Pneumocystis Pneumonia (PCP), among others.2

How common is HIV?

It has been estimated that roughly 1.1 million Americans are living with HIV, and about 15 percent are unaware of their status (have not yet been diagnosed).3,4 This number is even higher for specific age groups. For example, 51 percent of Americans with HIV between the ages of 13 and 24 are unaware they have the condition.3 Of the new diagnoses made each year in America, the majority are from the South. For example, in 2017, nearly 20,000 of the 38,000 new diagnoses came from the South alone, with this region making up over half of all new diagnoses.3

New diagnoses are most common in gay and bisexual men, or other men who have sex with men. This group made up 66 percent of all new diagnoses in 2017, and 82 percent of all male diagnoses. Of this group, African American men were the most commonly diagnosed, followed by Hispanic and Latino men, and white men.3,4

Global impact of HIV

Beyond the United States, HIV is a global concern. The World Health Organization (WHO) estimates that nearly 37 million people are living with HIV across the world, with nearly 26 million of these individuals residing in Africa. Beyond Africa, the WHO estimates that Southeast Asia has about 3.5 million individuals living with HIV, the Americas have 3.4 million, and Europe has 2.3 million living with the virus.5 Of the nearly 37 million with HIV worldwide, about 21.7 million are thought to be taking antiretroviral therapy (ART) to suppress their HIV, and only 75 percent are thought to be aware of their HIV status.5,6 Roughly 1.8 million children are living with HIV across the globe, with the highest concentration of these cases being in sub-Saharan Africa.7

How is HIV transmitted?

HIV is transmitted via infected bodily fluids. These fluids must come into contact with a non-infected individual’s mucous membranes or through a break in the skin (such as contact with an open wound) to have a chance of transmission. Mucous membranes include the inside lining of the vagina, anus, penis, mouth, eyes, and nose.1

Not all bodily fluids contain HIV. Contact with saliva, sweat, and tears cannot lead to HIV transmission. The bodily fluids that can contain HIV include:

  • Blood
  • Semen
  • Pre-seminal fluid (also called precum)
  • Rectal fluids
  • Vaginal fluids
  • Breast milk1

The highest risk behaviors for transmitting HIV are having unprotected anal or vaginal sex with someone with the virus and sharing needles or other injection drug equipment with someone with HIV. HIV can also be transmitted to the child of an HIV-positive woman during pregnancy, childbirth, or through breastfeeding. This is called mother-to-child transmission or vertical transmission. Other, less common methods of transmitting HIV include having oral sex with an HIV-positive partner, or, rarely, being accidentally stuck with a sharp object or needle that is contaminated with the virus.1

Reducing HIV risk

There are ways to reduce HIV transmission, including antiretroviral therapy (ART), using condoms and lubrication during sex, practicing safer drug injection or preparation techniques, and taking preventative medications either before being exposed to the virus (pre-exposure prophylaxis, PrEP) or immediately after (post-exposure prophylaxis, PEP). ART does not cure HIV, but it does involve using several different medications together to prevent the multiplication of HIV within the body. These medications are intended to be used daily, and if used as directed, can help reduce an individual’s viral load. A viral load is a measure of how much HIV is in the body.8,9

What does the term "undetectable" mean?

Eventually, a person’s viral load can become “undetectable” meaning that the amount of HIV in the blood is so low, that the virus is not detected when tested. Controlling viral load is essential for those with HIV to lead a longer life with fewer HIV-related complications.

Recent research has suggested that those who achieve and maintain, an undetectable viral load have virtually no risk of transmitting the virus to an HIV-negative partner. This idea has been referred to as “undetectable = untransmittable”” or “U=U. Therefore, the risk of HIV transmission to an HIV-negative partner can be reduced when an HIV-positive partner is on ART and taking their medications as prescribed.10,11

How long can people live with HIV?

Our understanding of HIV and its treatment has come a long way since the first cases of the virus were reported in the population. Although HIV can be a potentially life-threatening illness, the good news is that advances in treatment have increased life expectancy dramatically and have made the condition manageable. However, in order to see the benefits of treatment, it’s important to be adherent and follow your healthcare provider’s instructions as best as possible.

Studies have suggested that for an individual with HIV who takes their ART as directed, life expectancy is approaching, or even the same as, the general population.12-14 However, if an individual with HIV is not treated, or does not take their treatment consistently, their HIV can progress to AIDS, and they will be at risk for serious, life-threatening complications.

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