How HIV and AIDS Are Transmitted: Routes of Infection and Risk

HIV (human immunodeficiency virus) weakens the immune system and increases the risk of severe illnesses. AIDS is the late stage of HIV infection, a set of serious diseases caused by the virus. There is no cure, but with therapy most people with HIV live long and full lives.

HIV and AIDS: what is the difference

HIV infects immune system cells with CD4 receptors — T helper cells, macrophages, dendritic cells. Without treatment, the number of CD4+ T lymphocytes falls below 200 cells per microliter (normal 500–1200), and cellular immunity stops protecting the body. AIDS, or the late stage of HIV, is when tuberculosis, pneumonia, and tumors develop against the background of a destroyed immune system. Not everyone with HIV develops AIDS: with antiretroviral therapy the viral load becomes undetectable, and the person does not transmit the virus to others, including during unprotected sex.

How HIV is transmitted: the main routes of infection

The virus enters the bloodstream with infected biological fluids: blood, semen, vaginal secretions, and mucus from inside the anus. The most common route is vaginal, anal, or oral sex without a condom with a person who has the virus. HIV is also transmitted through sharing needles, syringes, and other equipment for injecting drugs, through shared sex toys, and from mother to child during pregnancy, childbirth, or breastfeeding when the viral load is detectable. Since 1985, blood transfusions have been screened for HIV, so the risk from donated blood is extremely low.

How HIV is not transmitted

You cannot become infected through kissing, hugging, handshakes, toilet seats, shared food, drinks, dishes, and ordinary household items. If a person is on effective therapy and has an undetectable viral load, they do not transmit the virus to a partner. For a healthcare worker who accidentally pricks themselves with an infected needle, the risk is also very low.

The likelihood of HIV infection through different contacts

The risk depends on the type of contact and the partner's viral load. It is higher with unprotected anal or vaginal sex, in the presence of other sexually transmitted infections, and with injecting drug use. We do not provide exact percentages for different contacts here: they depend on the partner's viral load and the type of contact.

• Unprotected vaginal or anal sex — the most common route of transmission.
• Shared needles and syringes for injections.
• Shared sex toys with a person with a detectable viral load.
• Transmission from mother to child during pregnancy, childbirth, or breastfeeding.

Condoms and withdrawal: what about the risk

A condom is the most effective protection against HIV and other sexually transmitted infections. It must be used before and during any contact between the penis, vagina, mouth, or anus. Water-based lubricants are used with condoms: oil-based ones (petroleum jelly, baby oil) destroy latex, and the condom breaks. Withdrawal is not a proven method of protection; a condom is considered reliable protection during sex.

HIV prevention and when to see a doctor

If you think you may have been exposed to HIV in the last 72 hours, urgently see an infectious disease doctor or go to an AIDS center / testing site — they may offer emergency prophylaxis (PEP), which can prevent infection. People at increased risk have access to PrEP — a preventive medication taken continuously or on demand. HIV testing, avoiding injecting drugs and shared needles, treating other sexually transmitted infections, and limiting the number of partners also reduce the risk. If the possible contact was more than 72 hours ago, see an infectious disease doctor or go to an AIDS center / testing site — you will be offered an HIV test. The test is done using saliva or a finger-prick blood sample; at a clinic the result is usually ready within a few days, and a home rapid test — within minutes. The first signs of HIV may appear after 2–6 weeks as a flu-like condition: fever, sore throat, enlarged lymph nodes, rash, aches, and fatigue. These symptoms are nonspecific, and years after infection may pass without complaints, so the only way to know your status is a test.

Suspicion of HIV alone is not a reason to call an ambulance; 103/112 — for a life-threatening condition (for example, severe chest pain or loss of consciousness).

This material is for reference: it explains the routes of transmission and protective measures, but does not replace a doctor's consultation — discuss the decision about testing and prevention with a specialist.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer