Human Immunodeficiency Virus (HIV) is a virus that targets and weakens the body’s immune system. Without effective management, this damage can lead to acquired immunodeficiency syndrome (AIDS). Understanding HIV transmission is fundamental for prevention, reducing misunderstanding and stigma, and promoting informed health decisions.
Understanding Transmission
HIV transmission occurs when certain bodily fluids from a person with HIV enter another person’s bloodstream. Transmissible fluids include blood, semen (including pre-seminal fluid), rectal fluids, vaginal fluids, and breast milk. These fluids must contact a mucous membrane (rectum, vagina, penis, mouth), damaged tissue (open cut or sore), or be directly injected into the bloodstream (e.g., via a needle).
The amount of HIV in a person’s blood, known as their viral load, significantly influences the likelihood of transmission. Individuals living with HIV who consistently take their prescribed medication can achieve an undetectable viral load. When the viral load is undetectable, the amount of virus in the body is so low that standard tests cannot measure it. Scientific evidence confirms that people with an undetectable viral load cannot sexually transmit HIV to their partners, a concept often summarized as “Undetectable = Untransmittable” or U=U.
Specific Modes of Transmission
Sexual contact is a common route for HIV transmission, particularly through unprotected anal or vaginal sex. During anal sex, the receptive partner has a higher likelihood of transmission. In vaginal sex, HIV can enter the body through the vaginal lining, cervix, urethra, or any cuts on the penis. Oral sex carries a very low risk, with transmission possible if open sores or bleeding gums are present.
Sharing needles or syringes is another mode of HIV transmission. This occurs when drug injection equipment or other sharp instruments contaminated with blood are shared. The virus can persist in a used needle for an extended period, making this a high-risk activity. Using new, sterile equipment for each injection prevents this transmission.
HIV can also be transmitted from a pregnant person to their child during pregnancy, childbirth, or through breastfeeding. This is referred to as mother-to-child or perinatal transmission. However, with proper medical care, including antiretroviral therapy (ART) for the pregnant person, the risk of transmission can be reduced to less than one percent. This involves consistent medication use throughout pregnancy, labor, delivery, and for the infant after birth.
Historically, blood transfusions and organ transplants posed a risk of HIV transmission. However, in countries with robust screening processes, this risk is now extremely rare. Donated blood and organs undergo rigorous testing for HIV and other pathogens, significantly reducing transmission through these medical procedures.
Activities That Do Not Transmit HIV
Many common activities do not transmit HIV, dispelling misconceptions and reducing fear. Casual contact, such as hugging, shaking hands, or sharing food or drinks, does not transmit the virus. HIV cannot survive long outside the human body, so it is not spread through contact with surfaces like toilet seats or shared utensils.
Activities involving public spaces, such as using public restrooms or swimming pools, carry no risk of HIV transmission. Insects, including mosquitoes, do not transmit HIV. The virus is not spread through saliva, tears, or sweat unless blood is visibly present. Donating blood is a safe process that does not transmit HIV, as new, sterile needles are used for each donor.