The human immunodeficiency virus (HIV) targets the immune system and weakens people's defense against many infections and some types of cancer. As the virus destroys and impairs the function of immune cells, infected individuals gradually become immunodeficient. Immune function is typically measured by CD4 cell count.
Immunodeficiency results in increased susceptibility to a wide range of infections, cancers and other diseases that people with healthy immune systems can fight off.
The most advanced stage of HIV infection is acquired immunodeficiency syndrome (AIDS), which can take many years to develop if not treated, depending on the individual. AIDS is defined by the development of certain cancers, infections or other severe long term clinical manifestations.
Signs and symptoms
The symptoms of HIV vary depending on the stage of infection. Though people living with HIV tend to be most infectious in the first few months after being infected, many are unaware of their status until the later stages. In the first few weeks after initial infection people may experience no symptoms or an influenza-like illness including fever, headache, rash or sore throat.
As the infection progressively weakens the immune system, they can develop other signs and symptoms, such as swollen lymph nodes, weight loss, fever, diarrhoea and cough. Without treatment, they could also develop severe illnesses such as tuberculosis (TB), cryptococcal meningitis, severe bacterial infections, and cancers such as lymphomas and Kaposi's sarcoma.
HIV can be transmitted via the exchange of a variety of body fluids from infected people, such as blood, breast milk, semen and vaginal secretions. HIV can also be transmitted from a mother to her child during pregnancy and delivery. Individuals cannot become infected through ordinary day-to-day contact such as kissing, hugging, shaking hands, or sharing personal objects, food or water.
It is important to note that people with HIV who are taking ART and are virally suppressed do not transmit HIV to their sexual partners. Early access to ART and support to remain on treatment is therefore critical not only to improve the health of people with HIV but also to prevent HIV transmission.
Behaviours and conditions that put individuals at greater risk of contracting HIV include:
- having unprotected anal or vaginal sex;
- having another sexually transmitted infection (STI) such as syphilis, herpes, chlamydia, gonorrhoea and bacterial vaginosis;
- sharing contaminated needles, syringes and other injecting equipment and drug solutions when injecting drugs;
- receiving unsafe injections, blood transfusions and tissue transplantation, and medical procedures that involve unsterile cutting or piercing; and
- experiencing accidental needle stick injuries, including among health workers
HIV can be diagnosed through rapid diagnostic tests that provide same-day results. This greatly facilitates early diagnosis and linkage with treatment and care. People can also use HIV self-tests to test themselves. However, no single test can provide a full HIV diagnosis; confirmatory testing is required, conducted by a qualified and trained health or community worker at a community centre or clinic. HIV infection can be detected with great accuracy using WHO prequalified tests within a nationally approved testing strategy.
Most widely-used HIV diagnostic tests detect antibodies produced by the person as part of their immune response to fight HIV. In most cases, people develop antibodies to HIV within 28 days of infection. During this time, people experience the so-called “window” period – when HIV antibodies haven’t been produced in high enough levels to be detected by standard tests and when they may have had no signs of HIV infection, but also when they may transmit HIV to others. After infection, an individual may transmit HIV transmission to a sexual or drug-sharing partner or for pregnant women to their infant during pregnancy or the breastfeeding period.
Following a positive diagnosis, people should be retested before they are enrolled in treatment and care to rule out any potential testing or reporting error. Notably, once a person diagnosed with HIV and has started treatment they should not be retested.
While testing for adolescents and adults has been made simple and efficient, this is not the case for babies born to HIV-positive mothers. For children less than 18 months of age, serological testing is not sufficient to identify HIV infection – virological testing must be provided as early as birth or at 6 weeks of age). New technologies are now becoming available to perform this test at the point of care and enable same-day results, which will accelerate appropriate linkage with treatment and care.
HIV can be suppressed by treatment regimens composed by a combination of 3 or more ARV drugs. Current ART does not cure HIV infection but highly suppresses viral replication within a person's body and allows an individual's immune system recovery to strengthen and regain the capacity to fight off infections.
Since 2016, WHO recommended that all people living with HIV be provided with lifelong ART, including children, adolescents and adults, and pregnant and breastfeeding women, regardless of clinical status or CD4 cell count.
By June 2020, 185 countries had already adopted this ‘treat all’ recommendation, covering 99% of all people living with HIV globally. In addition to ‘treat all’, WHO also recommend a rapid ART initiation to all people living with HIV, including offer ART on the same day of diagnosis among those who are ready to start treatment. By mid-2020, 70 low-and middle-income countries reported that they have adopted this policy, and approximately half of them reported country-wide implementation.
The current HIV treatment guidelines include new ARV options with better tolerability, higher efficacy, and lower rates of treatment discontinuation when compared with previous recommended medicines. In 2019, WHO recommended the use of dolutegravir-based or low-dose efavirenz for first-line therapy. DTG should also be used in 2nd line therapy, if not used in 1st line and darunavir/ritonavir is recommended as the anchor drug in third- line or an alternative option second-line therapy.
By June 2020, transition to dolutegravir had been implemented in 100 low- and middle-income countries and is expected to improve the durability of the treatment and the quality of care for people living with HIV. Despite improvements, limited options remain for infants and young children. For this reason, WHO and partners are coordinating efforts to enable a faster and more effective development and introduction of age-appropriate paediatric formulations of new ARV drugs.
In addition, one third of people living with HIV present to care with advanced disease, usually with severe clinical symptoms, low CD4 cell counts, and at high risk of developing serious illness and death. To reduce this risk, WHO recommends that these individuals receive a “package of care” that includes screening tests and drug prophylaxis for the most common serious infections that can cause severe morbidity and death, such as TB and cryptococcal meningitis, in addition to rapid ART initiation.
Globally, 25.4 million people living with HIV were receiving ART in 2019. This equates to a global ART coverage rate of 67%. However, more efforts are needed to scale up treatment, particularly for children and adolescents. Only 53% of children were receiving ART at the end of 2019.