HIV and AIDS: Risks, Diagnosis, Treatment, and Prevention

What are HIV and AIDS?

HIV (Human Immunodeficiency Virus) is a virus that damages the immune system by progressively destroying white blood cells, specifically CD4+ T lymphocytes. This process leaves the body increasingly vulnerable to serious infections and certain types of cancer.

AIDS (Acquired Immune Deficiency Syndrome) is the condition of acquired immune deficiency that represents the final stage of HIV infection. It is characterized by a severely impaired immune system that can no longer adequately protect the body. Crucially, thanks to modern antiretroviral therapies, not all patients with HIV will progress to AIDS. In fact, for the vast majority of those diagnosed early and treated consistently, this progression is entirely preventable.

HIV is transmitted primarily through:

• Unprotected sexual intercourse
• Sharing contaminated needles or other injection equipment
• Contact with infected blood (including through transfusions in settings without adequate blood screening)
• Mother to child during pregnancy, childbirth, or breastfeeding if the mother is not on effective treatment

The first symptoms of HIV infection can be quite subtle, such as swollen lymph nodes and mild flu-like symptoms. In fact, many patients develop no noticeable symptoms for years. This makes the virus particularly difficult to detect without specific testing.

While there is no definitive cure that eliminates the virus from the body, medicine now has many effective drugs that suppress HIV replication, protect the immune system, and dramatically reduce the risk of transmission to others. People who receive early diagnosis and prompt treatment can live long, healthy lives comparable to the general population.

This article is the second part of our in-depth series on HIV. For information on causes, symptoms, transmission routes, and common myths, see the companion article: HIV Symptoms, Transmission, and Misconceptions.

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Dangers and Complications

The ultimate effect of HIV on the human body is the progressive weakening of the immune system. If left untreated, this weakening leads to the development of AIDS. It is therefore unsurprising that the most serious complications of HIV infection take the form of opportunistic infections and certain cancers. These are diseases that a healthy immune system would normally suppress or eliminate without difficulty.

It is important to emphasize, however, that patients who adhere rigorously to antiretroviral therapy maintain an active and functional immune system. As a result, the likelihood of developing these complications is dramatically reduced, often to near zero.

Opportunistic Infections

Opportunistic infections are infections caused by pathogens that are normally harmless (or kept under control) in people with intact immune systems, but which can cause severe, life-threatening disease when immunity is compromised. These represent the most common and serious complications of HIV/AIDS.

The following are the principal opportunistic infections and AIDS-defining conditions recognized by major health authorities:

• Candidiasis: Caused by the fungus Candida, a microorganism ordinarily present in the body without causing harm. In immunocompromised individuals, it can cause infections of the skin, nails, and mucous membranes, including the vagina, penis, and mouth (oral thrush). In people with HIV, candidiasis is especially dangerous and considered an AIDS-defining condition when it infects the esophagus or the lower respiratory tract. Infection of the esophagus leads to painful swallowing and difficulty eating. Meanwhile, infection of the lower respiratory tract, which includes the trachea, bronchi, or lung tissue, can cause severe complications.

• Invasive cervical carcinoma: This cancer initially affects the cervix, which is the lower part of the uterus that opens into the vagina. In immunocompromised individuals, it can spread aggressively to other parts of the body. Regular cervical cancer screening (Pap smear and HPV testing) is particularly important for women living with HIV.

• Coccidioidomycosis: Caused by the fungus Coccidioides immitis, spread by inhaling fungal spores from contaminated soil. It can cause pneumonia and, in people with advanced HIV, can disseminate beyond the lungs to other organs. More common in parts of the Americas, particularly in arid regions.

• Cryptococcosis: Caused by Cryptococcus neoformans, a fungus found in soil and bird droppings. It typically enters through the lungs and can cause severe pneumonia. However, it is particularly feared for its ability to spread to the central nervous system, where it may lead to cryptococcal meningitis: a potentially fatal inflammation of the membranes surrounding the brain.

• Cryptosporidiosis: A parasitic diarrheal disease caused by the protozoan Cryptosporidium. Symptoms include severe, profuse watery diarrhea and abdominal cramps, which can be debilitating and lead to serious malnutrition and dehydration in immunocompromised patients.

• Cytomegalovirus (CMV): A very common herpesvirus that causes few or no symptoms in healthy individuals. In people with severely compromised immunity, CMV can cause life-threatening diseases such as pneumonia, gastroenteritis, and encephalitis. It may also lead to CMV retinitis, a progressive viral infection of the retina that can cause blindness if left untreated.

• HIV-associated encephalopathy (HIV-associated neurocognitive disorder, HAND): A spectrum of neurological complications caused directly by HIV’s effects on the central nervous system. In its most severe form, it presents as progressive cognitive decline, motor dysfunction, and behavioral changes. The exact mechanisms are multifactorial and incompletely understood.

• Herpes simplex virus (HSV) disease: HSV is extremely common in the general population, where it typically causes recurrent cold sores or genital herpes. In people with severely damaged immune systems, HSV can cause severe, chronic ulcers, as well as bronchitis, pneumonia, and esophagitis.

• Histoplasmosis: Caused by Histoplasma capsulatum, a fungus found in soil enriched with bird or bat droppings, particularly in river valleys. Inhalation of spores can cause flu-like symptoms or pneumonia. In immunocompromised patients, the infection can disseminate widely to involve the liver, spleen, bone marrow, and other organs.

• Isosporiasis (Cystoisosporiasis): A parasitic intestinal infection caused by Cystoisospora belli. It causes chronic, severe diarrhea in immunocompromised patients and has become more prevalent in the context of HIV/AIDS.

• Kaposi’s sarcoma: A cancer caused by Human Herpesvirus 8 (HHV-8). It causes the abnormal growth of small blood vessels, producing characteristic pink or purple skin lesions (patches, plaques, or nodules) that can appear anywhere on the body. Kaposi’s sarcoma becomes life-threatening when it involves internal organs such as the lungs, lymph nodes, or gastrointestinal tract. It was one of the first recognized AIDS-defining conditions and was historically a common presentation of advanced AIDS.

• Lymphomas: HIV-associated lymphomas include both Non-Hodgkin lymphoma and Hodgkin lymphoma, as well as primary central nervous system lymphoma. People with HIV have a significantly elevated risk of developing these blood cancers. Non-Hodgkin lymphoma in particular is an AIDS-defining malignancy.

• Tuberculosis (TB): Caused by Mycobacterium tuberculosis, tuberculosis is the leading cause of death among people living with HIV worldwide, responsible for approximately one-third of all AIDS-related deaths globally. TB spreads through the air when a person with active pulmonary TB coughs, sneezes, or speaks. Symptoms include persistent cough, fatigue, weight loss, fever, and night sweats. While TB primarily affects the lungs, it can spread to virtually any organ, including the lymph nodes, brain, kidneys, and bones. HIV infection dramatically increases the risk of both developing active TB from latent infection and of rapid disease progression.

• Mycobacterium avium complex (MAC): A serious infection caused by environmental mycobacteria (Mycobacterium avium and M. intracellulare) that are ubiquitous in water, soil, dust, and food. In healthy individuals, these organisms cause no harm. In people with severely immunocompromised systems (CD4 count below 50 cells/mm³), MAC can cause disseminated disease involving the lungs, intestines, bone marrow, liver, and spleen, resulting in high fevers, severe weight loss, night sweats, and anemia.

• Pneumocystis jirovecii pneumonia (PCP): Also known historically as Pneumocystis carinii pneumonia, PCP was one of the most feared AIDS-defining illnesses before effective treatment became available. Caused by a fungus (Pneumocystis jirovecii), it presents as progressive breathlessness, dry cough, and low-grade fever. Without treatment, it can be rapidly fatal. PCP prophylaxis (with trimethoprim-sulfamethoxazole) is still recommended for patients with CD4 counts below 200 cells/mm³.

• Progressive multifocal leukoencephalopathy (PML): A rare but devastating viral disease of the central nervous system caused by reactivation of JC virus (John Cunningham virus) in severely immunocompromised patients. It causes progressive destruction of the myelin sheath (the protective covering of nerve fibers) at multiple sites in the brain, leading to cognitive decline, motor weakness, visual disturbances, and speech problems. It carries a poor prognosis.

• Salmonellosis: Salmonella bacteria enter the body through contaminated food or water. While salmonellosis usually leads to a self-limiting gastrointestinal illness in healthy individuals, with symptoms such as nausea, vomiting, and diarrhea, it can result in recurrent, severe bacteremia (blood poisoning) in immunocompromised patients. In these cases, recurrence of the condition is considered an AIDS-defining illness.

• Cerebral toxoplasmosis: Caused by the parasite Toxoplasma gondii (commonly acquired from cat feces or undercooked meat), toxoplasmosis is generally benign in immunocompetent adults. In severely immunocompromised individuals, particularly those with CD4 counts below 100 cells/mm³, the parasite can reactivate and cause cerebral toxoplasmosis. This condition leads to brain abscesses, which present with headaches, confusion, fever, seizures, and focal neurological deficits. It is a medical emergency.

• AIDS wasting syndrome: Defined as involuntary loss of more than 10% of body weight accompanied by chronic diarrhea (lasting more than 30 days), persistent weakness, or fever for more than 30 days in the absence of another explanatory illness. Wasting reflects profound metabolic disruption and is associated with significant loss of lean muscle mass.

Emergency Post-Exposure Treatment (PEP)

If you believe you may have been exposed to HIV within the last 72 hours (3 days), for instance through unprotected sex with a partner who may be HIV-positive, a needlestick injury with a contaminated needle, or sexual assault, you could qualify for a treatment called PEP (Post-Exposure Prophylaxis). This treatment can greatly reduce your risk of acquiring the infection.

Time is critical: PEP must be started as soon as possible after the exposure. Ideally, this should be within a few hours, and no later than 72 hours. After 72 hours, PEP is no longer considered effective and will not be prescribed.

PEP is recommended following:

• Unprotected sexual intercourse with an HIV-positive partner not on effective suppressive therapy
• Sexual contact with a partner of unknown HIV status in a high-risk context
• Sharing of needles or injection equipment with a person of known or unknown HIV status
• Occupational exposures (e.g., needlestick injuries in healthcare settings)

How PEP works: PEP consists of a 28-day course of antiretroviral drugs, typically a combination of two or three medications taken daily. Modern PEP regimens have an excellent tolerability profile, although some individuals experience initial side effects such as nausea or mild sleep disturbances, which typically resolve within the first few weeks.

PEP is not a “morning after” pill for HIV. It does not guarantee 100% protection against infection, and its effectiveness relies entirely on strict adherence to the full 28-day course. Missing doses reduces its efficacy significantly.

After starting PEP:

• Maintain regular medical follow-up to monitor for side effects and assess treatment response.
• Undergo HIV testing at baseline (when starting PEP), at 6 weeks, 3 months, and 6 months after the exposure.
• Talk to your doctor about long-term prevention strategies. If you face ongoing and sustained risk of HIV exposure, consider PrEP (Pre-Exposure Prophylaxis) in particular.

Where to access PEP: PEP is available at hospital emergency departments, sexual health clinics, and infectious disease units in many countries. Availability and access may vary depending on the local healthcare system. If you think you need PEP, do not wait; seek medical attention immediately.

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Diagnosis

HIV diagnosis today is a rapid, highly accurate, and strictly confidential process. Getting tested is the only way to know your HIV status. The virus can remain completely silent for many years, causing no detectable symptoms, while still damaging the immune system and remaining transmissible to others.

Who Should Get Tested

Major health guidelines recommend HIV testing for anyone who has been in a situation involving potential risk, including:

• Unprotected sexual intercourse (even a single instance).
• Sharing injection equipment (needles, syringes, or other drug paraphernalia).
• A sexual partner with confirmed or suspected HIV infection.
• A diagnosis of another sexually transmitted infection (STI).
• Pregnancy, as part of routine antenatal screening (see Screening During Pregnancy).
• Any symptoms potentially compatible with opportunistic infections.
• As part of routine periodic health screening for sexually active individuals, many guidelines recommend HIV testing at least once in a lifetime for all adults. They also advise regular testing for those at higher risk.

There is no shame and no risk in getting tested. Knowing your status is an act of responsibility toward yourself and your partners.

Available Tests and the Window Period

The single most important concept in HIV diagnosis is the window period. This refers to the interval of time between the moment of infection and when a test can reliably detect the infection. Different test types have different window periods.

• Fourth-generation combination tests (Combo/Duo tests): These are the current standard used in hospitals and specialized centers. They simultaneously detect two markers:
  • Anti-HIV-1 and anti-HIV-2 antibodies: produced by the immune system in response to HIV.
  • p24 antigen: a viral protein that appears in the blood very early, typically 2–4 weeks after infection. It shows up before antibodies are detectable, dramatically shortening the window period.

With fourth-generation HIV tests, infection can often be detected within a few weeks after a potential exposure. The time required for a test to reliably rule out infection depends on the specific test, the timing of testing, and applicable clinical guidelines. A negative result obtained after the recommended window period for the test is considered conclusive according to the relevant testing guidance.

• Rapid tests and self-tests: Available at pharmacies, community health centers, and NGO-run “checkpoint” sites, or for home use. They can be performed on fingertip capillary blood (finger prick) or oral fluid (saliva). Most rapid and self-tests detect antibodies only (not p24 antigen), which means they have a longer window period of approximately 90 days. A negative result from these tests is only definitively conclusive if the test is performed at least 3 months after the potential exposure. Any positive (reactive) result from a rapid or self-test always requires official laboratory confirmation.

• Molecular tests (NAT/PCR): These tests detect HIV RNA (the virus’s genetic material) directly in the blood, without waiting for the immune system to produce antibodies. They have the shortest window period (approximately 10–12 days) and the highest sensitivity. NAT tests are used primarily for: screening donated blood and organs, diagnosing HIV in newborns of HIV-positive mothers (where maternal antibodies make antibody tests unreliable for up to 18 months), and resolving indeterminate results in standard testing.

What to Do if You Test Positive

A reactive (positive) result on an initial screening test is not a confirmed diagnosis, so it must always be verified. The standard protocol is:

1. Confirmatory testing: A second blood sample is analyzed using a more specific confirmatory test. Traditionally, this has been the Western Blot or a modern supplemental immunoassay, both of which identify antibodies against specific individual HIV proteins. Only when the confirmatory test is also positive is the diagnosis considered definitive.

2. Specialist referral: Following confirmed diagnosis, the patient is immediately referred to a specialized infectious disease center. Current protocols ensure rapid, seamless care coordination.

3. Baseline assessment: A comprehensive evaluation is performed, including:

   • Viral load (HIV-RNA) measurement.
   • CD4+ T lymphocyte count.
   • Resistance genotyping (to identify drug-resistant mutations and select the most effective treatment).
   • Complete metabolic panel, liver and kidney function tests, STI screening, hepatitis B and C serology, cardiovascular risk assessment, and tuberculosis screening.

4. Immediate treatment initiation: In line with current Test and Treat guidelines, antiretroviral therapy is started as soon as possible after diagnosis. This approach applies regardless of CD4 count and aims to protect immune function while preventing transmission.

Confidentiality: In most high-income countries, HIV test results are protected by medical confidentiality and privacy laws. Your results generally cannot be disclosed to employers, family members, or other third parties without your consent, subject to applicable local laws and regulations.

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Treatment and Cure

While a definitive cure that eliminates HIV from the body does not yet exist, HIV infection is today considered a fully manageable chronic condition. The goals of modern therapy are clear:

1. Achieve and maintain undetectable viral load (complete suppression of viral replication)
2. Allow immune system recovery (rising CD4+ T cell counts)
3. Prevent the development of AIDS and its associated complications
4. Eliminate the risk of sexual transmission to others (U=U principle)
5. Ensure the patient lives a long, healthy, high-quality life

Antiretroviral Therapy (ART)

The cornerstone of HIV treatment is Highly Active Antiretroviral Therapy (HAART). This approach involves a combination of drugs from different classes, with each one blocking a distinct step in HIV’s replication cycle. Using multiple drugs simultaneously prevents the emergence of drug-resistant viral strains.

Efficacy and simplicity of modern regimens

In the early years of HIV treatment, patients were required to take upwards of 20 pills per day on complex schedules with significant food restrictions. Today, the vast majority of patients are treated with a Single Tablet Regimen (STR), which is a single pill taken once a day. This pill contains a fixed-dose combination of two or three antiretroviral agents. This has dramatically simplified adherence and transformed quality of life for people living with HIV.

Common drug classes used in modern regimens include:

• Integrase strand transfer inhibitors (INSTIs): For example, dolutegravir, bictegravir, and cabotegravir. This class is currently preferred because of its high efficacy, excellent tolerability, and high barrier to resistance.
• Nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs): For example, tenofovir alafenamide (TAF) and emtricitabine, which form the backbone of most regimens.
• Non-nucleoside reverse transcriptase inhibitors (NNRTIs): e.g., rilpivirine, doravirine.
• Boosted protease inhibitors (PIs): For example, darunavir, which is used in specific clinical situations.

Long-acting injectable therapies

The most innovative advance in HIV treatment in recent years is the availability of long-acting injectable formulations that eliminate the need for a daily pill.

• Cabotegravir + rilpivirine (Cabenuva): Administered as two intramuscular injections given by a healthcare professional every two months. Approved for patients who are already virologically stable on oral ART, this represents a major quality-of-life benefit and may improve adherence for some patients.
• Research in progress: Clinical trials are advancing toward every-six-month injection schedules using lenacapavir (a novel capsid inhibitor), and other even longer-acting formulations are in development.

Tolerability

New-generation antiretroviral drugs are extremely well tolerated by the vast majority of patients. Any initial side effects, like mild nausea or sleep disturbances, typically resolve within the first few weeks of treatment. Long-term toxicities that were associated with older drug classes (such as peripheral neuropathy or lactic acidosis) are now rare with modern regimens.

The U=U Principle: Undetectable = Untransmittable

One of the most transformative scientific discoveries in HIV medicine, and one of the most important messages for public health and reducing stigma, is this.

A person living with HIV who is on effective antiretroviral therapy, with a viral load that has been undetectable (below 50 copies/mL) for at least six months, cannot sexually transmit HIV to their partners.

This is the U=U (Undetectable = Untransmittable) principle. The findings are supported by three landmark prospective clinical studies: HPTN 052, PARTNER, and Opposites Attract. Together, these studies observed zero linked HIV transmissions. This finding comes from thousands of serodiscordant couples (one partner HIV-positive, the other HIV-negative) who engaged in condomless sex while the HIV-positive partner maintained a sustained undetectable viral load.

U=U has been formally endorsed by the CDC, NIH, NHS, WHO, and virtually all major infectious disease societies worldwide.

This principle has revolutionized the lives of people living with HIV, enabling them to maintain intimate relationships, plan families naturally, and live free from fear of transmission to loved ones. It is also one of the most powerful arguments against HIV-related stigma and discrimination.

Important caveat: U=U applies only when the HIV-positive partner has a confirmed, sustained undetectable viral load achieved through consistent ART adherence. It does not apply to individuals who do not know their status, are not on treatment, or who have intermittent viral suppression. Condoms remain the best protection against all STIs and are essential outside established, mutually tested relationships.

Lifestyle and Adherence

Adherence is the single most critical factor determining the success of HIV treatment. Taking antiretroviral medications at the same time every day, without missing doses, is essential to:

• Maintain undetectable viral load
• Prevent the development of drug-resistant viral strains (which can severely limit future treatment options)
• Protect the immune system from further damage
• Maintain the non-infectious state (U=U)

Beyond medication, a comprehensive healthy lifestyle plays a crucial role in long-term outcomes for people living with HIV:

• Nutrition and physical activity: A balanced diet and regular exercise are fundamental to preventing the long-term complications associated with HIV-related chronic inflammation and some antiretroviral drugs. These complications include cardiovascular disease, dyslipidemia, insulin resistance, and osteoporosis. Weight-bearing exercise in particular helps maintain bone density.

• Smoking cessation: People living with HIV who smoke have a significantly higher risk of cardiovascular disease, lung disease, and certain cancers than HIV-negative smokers or non-smoking people with HIV. Smoking cessation is arguably the most impactful lifestyle change a person with HIV can make. Support programs and pharmacotherapy (nicotine replacement, varenicline) should be actively offered.

• Alcohol and substance use: Excessive alcohol consumption can impair adherence, interact with medications, and contribute to liver disease (particularly in patients with hepatitis C coinfection). People who inject drugs should be supported with harm reduction programs and addiction treatment services.

• Psychological support: Receiving an HIV diagnosis can be profoundly challenging emotionally. Anxiety, depression, and social isolation are more common in people living with HIV than in the general population, partly as a consequence of persistent stigma. Psychological support from trained mental health professionals, as well as peer support groups and community organizations, are an integral part of comprehensive HIV care and should be proactively offered to all patients.

• Regular specialist follow-up: Scheduled visits every 3–6 months with an HIV specialist are essential to monitor viral load, CD4 count, medication tolerability, metabolic parameters, and overall health. Staying engaged with care is the foundation of long-term well-being.

Managing HIV in Children and Vaccinations

In the rare cases of pediatric HIV infection, which are now extremely uncommon in countries with universal antenatal screening and effective treatment, therapy is individualized. It depends on the child’s age, weight, and clinical status, and uses formulations specifically designed for pediatric use.

Children living with HIV can and should follow the standard vaccination schedule, including vaccines for measles, mumps, and rubella. Live attenuated vaccines may be contraindicated, however, in children with severe immunosuppression (very low CD4+ cell counts), and vaccine decisions should be made in consultation with a pediatric infectious disease specialist.

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Pregnancy

The possibility of a healthy pregnancy and a healthy baby is a reality for women living with HIV today. Antiretroviral therapy during pregnancy is the cornerstone of preventing mother-to-child transmission (vertical transmission) of HIV.

Without treatment, the risk of transmitting HIV to the baby is estimated at 15–45% (depending on mode of delivery and breastfeeding practices). With appropriate antiretroviral treatment initiated during pregnancy and maintained throughout, this risk falls to less than 1%. In some studies, it even approaches near zero.

Key principles of HIV management in pregnancy:

• Antiretroviral therapy: All pregnant women with HIV should receive effective ART regardless of their CD4 count or viral load. The goal is to achieve and maintain an undetectable viral load before and throughout delivery.

• Mode of delivery: For women with undetectable viral load (<50 copies/mL) at the time of delivery, vaginal birth is considered safe and is offered as a standard option. The choice between vaginal delivery and planned cesarean section is evaluated on a case-by-case basis by the medical team, taking into account viral load, gestational age, obstetric factors, and patient preference.

• Neonatal prophylaxis: Newborns of HIV-positive mothers receive a short course of antiretroviral drugs after birth as an additional protective measure, regardless of the mother’s viral load.

• Breastfeeding: In many high-income countries, mothers living with HIV may be advised not to breastfeed, as breast milk can transmit HIV. Safe infant formula may be recommended as a substitute. In low- and middle-income settings, where safe formula is not consistently available or affordable, the WHO recommends exclusive breastfeeding for the first 6 months. This recommendation applies if the mother is on effective ART with a suppressed viral load, as the benefits of breastfeeding may outweigh the small remaining risk of transmission.

• Conception planning: If one or both partners are living with HIV, it is strongly recommended to consult with an HIV specialist before attempting to conceive, to optimize treatment and explore conception strategies that minimize any risk of transmission to the uninfected partner.

For a comprehensive guide to HIV and pregnancy, including conception strategies for serodiscordant couples, see: HIV and Pregnancy.

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Prevention

Preventing HIV transmission remains a global public health priority. Despite decades of intensive research, no vaccine against HIV has yet been approved for clinical use. However, several candidates are now in advanced clinical trials, utilizing innovative mRNA and viral vector platforms.

In the absence of a vaccine, HIV can only be prevented by avoiding risky behaviors and using the pharmacological and barrier tools available.

The most effective HIV prevention strategy combines multiple approaches:

1. Using condoms consistently during all penetrative sexual activity
2. Never sharing injection equipment (needles, syringes, cotton filters, spoons)
3. PrEP (Pre-Exposure Prophylaxis) for high-risk HIV-negative individuals
4. PEP (Post-Exposure Prophylaxis) following accidental exposures
5. HIV testing and treatment (Treatment as Prevention / U=U)
6. Regular STI testing and treatment, as STIs significantly increase HIV transmission risk

Behaviors and situations that carry no risk of HIV transmission include:

• Hugging, handshaking, or other casual physical contact
• Sharing glasses, cups, plates, or cutlery
• Sneezing or coughing
• Mosquitoes or other insects
• Sharing towels, toilet seats, or door handles

While everyday household items are safe to share, it is advisable not to share toothbrushes or razors, as these can carry traces of blood.

The role of alcohol and drug use in HIV prevention: Avoiding or limiting alcohol and recreational drug use is important. These substances don’t directly transmit HIV, but intoxication impairs judgment and decision-making. As a result, individuals may be more likely to engage in unprotected sex or share injection equipment. Substance use disorders should be treated as health conditions, with access to counseling, harm reduction programs, and addiction treatment services.

Sexual Intercourse

HIV can be transmitted through vaginal, anal, or oral sex in the absence of adequate protection. The risk varies significantly by type of activity (as detailed in our companion transmission guide):

• Anal intercourse carries the highest risk, particularly for the receptive partner
• Vaginal intercourse carries significant risk for both partners, higher for the receptive partner
• Oral sex carries a low but non-negligible risk, especially with ejaculation or in the presence of oral wounds or STIs

HIV can also be transmitted through shared sex toys if they have been used by an infected person without being cleaned or covered with a new condom between uses.

The condom is the most effective barrier protection against HIV and other STIs and must be used for:

• Anal intercourse
• Vaginal intercourse
• Oral sex on a penis (male condom) or a vulva/anus (dental dam)

Critical points about correct condom use:

• HIV can be transmitted before ejaculation, through pre-seminal fluid and vaginal secretions. The condom must therefore be put on before any genital contact, not just before ejaculation.
• Only water-based lubricants should be used with latex condoms. Oil-based lubricants (such as petroleum jelly, baby oil, or coconut oil) degrade latex and increase the risk of condom breakage. Water-based lubricants also reduce vaginal and anal friction, decreasing the risk of micro-tears (which increase HIV transmission risk) and reducing condom failure.
• Female condoms (internal condoms) are also effective and provide an alternative for those who prefer them or whose partners refuse male condoms.

The role of STIs in HIV risk: Having an active sexually transmitted infection, particularly those that cause genital ulcers or sores like herpes, syphilis, or chancroid, significantly increases the risk of both acquiring and transmitting HIV. STIs cause mucosal inflammation and disrupt the skin barrier, creating entry points for the virus. Regular STI screening and prompt treatment are therefore an important component of HIV prevention.

Comprehensive sexual health education is essential for preventing HIV and other STIs, including chlamydia, gonorrhea, hepatitis B, syphilis, and genital warts.

Sharing Injection Equipment

For people who use injectable drugs, never sharing needles, syringes, cotton filters, spoons, or any other injection equipment is the most important step in preventing blood-borne HIV transmission. Sharing equipment can also transmit hepatitis C and hepatitis B.

Harm reduction resources:

• Needle and syringe programs (NSPs): Many public health authorities, pharmacies, and community organizations offer needle exchange programs where used needles can be exchanged for new, sterile ones free of charge and without judgment. These programs are evidence-based public health interventions that reduce HIV transmission without increasing drug use.

• Opioid substitution therapy: For individuals with opioid use disorder (including heroin dependency), methadone maintenance treatment or buprenorphine therapy provides a medically supervised, orally administered alternative that eliminates the risks associated with injection drug use. These programs are available through specialized addiction medicine services in many countries.

• Safer use supplies: Single-use sterile equipment should always be used for tattooing and body piercing. Reputable tattoo and piercing studios use disposable needles and sterilized equipment as standard practice.

HIV Screening During Pregnancy

HIV testing is offered to all pregnant women as part of routine prenatal (antenatal) screening. Ideally, this should occur in the first trimester of pregnancy. If a woman presents later in pregnancy, testing should take place at the first prenatal visit.

This recommendation exists because untreated HIV infection in pregnancy can be transmitted to the baby during pregnancy, labor, delivery, or breastfeeding. Without intervention, the transmission risk can reach up to 45%. With prompt diagnosis and effective antiretroviral treatment, this risk is reduced to less than 1%.

HIV testing in pregnancy is offered as a standard component of antenatal care in many countries. Women who test negative early in pregnancy but have ongoing risk factors may be offered repeat testing in the third trimester.

For a full guide to HIV in the context of pregnancy and family planning, see: HIV and Pregnancy.

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Sources and Bibliography

• CDC: Living with HIV: Opportunistic Infections
• NHS: HIV and AIDS
• World Health Organization (WHO) HIV/AIDS Fact Sheet
• UNAIDS: Global HIV & AIDS Statistics
• European AIDS Clinical Society (EACS): Guidelines for the Treatment of People Living with HIV
• CDC: HIV Treatment: The Basics
• NIH NIAID: 10 Things to Know About HIV Suppression
• NHH: HIV Prevention
• Cohen MS, et al. Antiretroviral therapy for the prevention of HIV-1 transmission (HPTN 052). N Engl J Med. 2016. DOI: 10.1056/NEJMoa1600693
• Rodger AJ, et al. Risk of HIV transmission through condomless sex in serodifferent gay couples with the HIV-positive partner taking suppressive antiretroviral therapy (PARTNER2). Lancet. 2019. DOI: 10.1016/S0140-6736(19)30418-0
• Bavinton BR, et al. Viral suppression and HIV transmission in serodiscordant male couples (Opposites Attract). Lancet HIV. 2018. DOI: 10.1016/S2352-3018(18)30132-2
• Survival of HIV-positive patients starting antiretroviral therapy between 1996 and 2013: a collaborative analysis of cohort studies. The Lancet HIV. 2017.
• Panel on Antiretroviral Guidelines for Adults and Adolescents. Guidelines for the Use of Antiretroviral Agents in Adults and Adolescents with HIV. NIH AIDSinfo. 2024.
• WHO. Consolidated Guidelines on HIV Prevention, Testing, Treatment, Service Delivery and Monitoring. Geneva: World Health Organization; 2021.