Human immunodeficiency virus (HIV)

Last Review Date: September 3, 2015

What is HIV?

HIV (human immunodeficiency virus) is the virus that causes AIDS (acquired immunodeficiency syndrome). By killing or damaging cells of the body's immune system, HIV progressively destroys the body's ability to fight infections and certain cancers. People diagnosed with AIDS may get life-threatening diseases called opportunistic infections, which are caused by microbes such as viruses or bacteria that usually do not make healthy people sick.

How is HIV transmitted?

HIV is spread most commonly in these ways:

  • By having unprotected sex with an infected partner. The virus can enter the body through the lining of the rectum, vagina, vulva, penis, or mouth during sex. Having a sexually transmitted disease such as syphilis, genital herpes, chlamydia, gonorrhoea, bacterial vaginosis or trichomoniasis makes people more susceptible to acquiring HIV infection during sex with infected partners.
  • Through contact with infected blood. Before blood was screened for HIV infection and before techniques were introduced to destroy HIV in blood products, HIV was sometimes transmitted through transfusions of contaminated blood or blood products. Today, because of blood screening and heat treatment of blood derivatives, the risk of getting HIV from blood products in Australia is extremely small.
  • By sharing needles or syringes (such as during drug use), the virus can be transmitted from the very small amount of blood remaining on the needle. Uncommonly, HIV is transmitted to health care workers or others from needle-stick injuries or other infected medical instruments.
  • To the newborn during pregnancy or birth. Approximately one-quarter to one-third of all untreated pregnant women infected with HIV will pass the infection to their babies. HIV also can be spread to babies through the breast milk of mothers infected with the virus. However, with appropriate treatment of the mother during pregnancy and the baby after birth, the risk of the newborn becoming infected is very small.
  • It is important to know HIV cannot be transmitted by mosquito or other insect bites. It cannot be spread by contact with tear, sweat or saliva (being spit on) or through physical contact such as hugging, holding hands, closed mouth kissing, using the same toilet or sharing  utensils. It is also extremely unlikely for HIV to be transmitted via open-mouth kissing although this is theoretically possible if there are open sores or blood is present. 

What tests are used to diagnose and monitor HIV?

There are several types of tests associated with HIV disease. Some test for antibodies that the body makes in response to the virus, some test for the concentration of a protein (called p24) found in the virus, some test for the actual number of copies of the virus per millilitre of blood (called viral load testing), some test for levels of immune cells called CD4 cells that are attacked by HIV, and some test for whether patients are resistant to anti-HIV drugs.

  • Antibody testing—to diagnose HIV infection. This test can miss very early HIV infection and should therefore be repeated if there is a high concern about HIV infection.
  • p24 protein testing - may be used to detect early HIV infection. It is now incorporated into most HIV screening tests as a combined antigen/antibody assay.
  • HIV Western Blot - used to confirm HIV infection when an antibody screening test is positive.
  • Multispot HIV-1/HIV-2 test - a rapid enzyme immunoassay used for the detection and differentiation of HIV-1 and HIV-2 antibodies.
  • Viral load testing - determines the amount of virus present in a patient's bloodstream. It is used to decide when to start therapy and to monitor therapy and HIV progression.
  • CD4 T-cell testing—to decide when to start therapy and to monitor therapy, HIV progression, and the status of the immune system.
  • Genotypic resistance testing—to determine if a particular strain of HIV is resistant to the therapy you are on and if the therapy should be switched.

When are these tests requested?

One or more of these tests are ordered after a person is exposed to HIV and decides to be tested, either at the doctor's surgery or a local clinic. Several of the tests listed above are then requested at intervals by a doctor to monitor the course of therapy.

What are the early symptoms of HIV?

Many people do not develop any symptoms when they first become infected with HIV. Some people, however, have a flu-like illness within two weeks of exposure to the virus. This illness may include fever, headache, rash, and enlarged lymph nodes (tender glands usually felt in the neck and groin). These symptoms usually disappear within a week to a month and are often mistaken for those of another viral infection. During this period people are very infectious and HIV is present in large quantities in genital fluids.

More persistent or severe symptoms may not surface for a decade or more after HIV first enters the body in adults, or within two years in children born with HIV infection. This period of "asymptomatic" infection is highly individual. Some people may have symptoms in a few months, while others may be symptom-free for more than 10 years. During the asymptomatic period, however, the virus is actively multiplying, infecting, and killing immune system cells.

The effect of HIV is most obvious in the decline in the blood levels of your CD4 T cells (also called T4 cells), the immune system's key infection fighters. At the beginning of its life in the human body, the virus disables or destroys these cells without causing symptoms.

As the immune system deteriorates, a variety of complications occur. For many people, their first sign of infection is large lymph nodes or “swollen glands” that may be enlarged for more than three months. Other symptoms often experienced months to years before the onset of AIDS include:

  • lack of energy
  • weight loss
  • frequent fevers and sweats
  • More frequent infections, such as recurrent yeast (thrush) infections, more frequent outbreaks of herpes sores or shingles, or episodes of pneumonia
  • persistent skin rashes or flaky skin
  • pelvic inflammatory disease (PID) in women that does not respond to treatment

When does AIDS develop?

The term AIDS applies to the most advanced stages of HIV infection. Generally speaking AIDS develops in those people who are not taking HIV medication, usually because they are unaware of their infection. But AIDS can develop on treatment, because the virus has developed drug resistance. 

The Centers for Disease Control (CDC) in Atlanta, USA, develops official criteria for the definition of AIDS. Their definition includes all HIV-infected people who have fewer than 200 CD4 T cells per microlitre of blood (i.e. less than 0.2 x 109/L). (Healthy adults usually have CD4 T-cell counts of 1,000 or more.) In addition, the definition includes 26 opportunistic infections that affect people who have advanced HIV disease.

Most of these conditions are called opportunistic infections because they rarely cause medical problems in healthy people. In people with AIDS, these infections are often severe and sometimes fatal because the immune system is so damaged by HIV that the body cannot fight off certain bacteria, viruses, fungi, parasites, and other microbes.

Opportunistic infections common in people with AIDS cause symptoms such as:

  • coughing and shortness of breath
  • seizures and lack of coordination
  • difficult or painful swallowing
  • mental symptoms such as confusion and forgetfulness
  • severe and persistent diarrhoea
  • fever
  • vision loss
  • feeling sick, abdominal cramps, and vomiting
  • weight loss and extreme fatigue
  • severe headaches, and
  • coma.

Common Questions

1. How do I know whether I should get tested for HIV?

It only takes one sexual encounter with an infected person to become infected. If you are concerned about HIV infection it is appropriate to be tested even if you are at low risk. Pregnant women are routinely tested for HIV infection. This is very important because HIV transmission to the baby can be prevented if the mother is treated.

You should especially consider getting tested if:

  • you have had sex with three or more partners
  • you are a man who has sex with men
  • you have paid for sex or had anonymous sex
  • you have had sex while travelling overseas
  • you have shared needles for injecting drugs
  • you have had a needle stick injury or are a health care worker with an occupational exposure to a patient's blood
2. How confidential are HIV test results?

Certain testing centres provide either anonymous (your name is never given) or confidential (your name is given but kept private) HIV testing and counselling.

3. Should I tell anyone else of my results?

Yes. If you test positive for HIV, it is important that you tell your health care providers as well as all current and future sex partners and/or anyone with whom you have shared needles. Counselling services are available that will help you to inform the people who need to know. For more information, visit AFAO: Recently diagnosed?.

4. Are there treatments for HIV/AIDS?

The good news is that the drug therapies for HIV are improving all the time. Now most patients with HIV on medication live a normal life free of illness. These medications work extremely well but they need to be taken very regularly or else drug-resistance and treatment failure may occur. Even those with advanced disease (AIDS) can return to near-normal health with medication. Current evidence suggests therapy should start as early as possible before the CD4 cells are depleted, because the immune system may not be able to completely recover from the damage HIV causes.

5. Can HIV transmission be prevented after exposure?

Yes. HIV transmission can be prevented by taking HIV medication soon after exposure to the virus. This treatment is available in most Australian hospital emergency departments. The treatment should be started as early as possible, by 72 hours it is too late to intervene. However as these medications need to be monitored closely and can cause side-effects it is important to consider the risks and benefits of such treatment carefully before starting. 

6. Does everyone who has HIV get AIDS?

With modern treatments HIV has become a chronic disease that can be kept under control for decades. For people who are infected with HIV now, as long as treatment is started early and not interrupted, they are unlikely to ever develop AIDS. Without treatment, almost all HIV positive people will eventually develop AIDS. The exception is a very small number of people who have been infected with HIV for over twenty years and have not developed AIDS, they are known as long-term non-progressors.

7. Can HIV infection be cured?

There has been one case of a potential cure reported in the scientific literature. The case was of a patient with lymphoma (a type of blood cancer) and HIV. In an attempt to cure this cancer the patient received a stem cell transplant (a transplant of precursor blood cells). The  donor CD4 cells had a rare mutation that can prevent HIV transmission. Prior to the transplantation the patient’s own immune cells, including those infected with HIV, were eradicated using powerful drugs and radiation. The patient has remained free of HIV since this treatment occurred in 2009. This type of treatment will never be an option for the vast majority of people infected with HIV.  

8. Can you get HIV/AIDS from donating blood?

No. It is very safe to donate blood because sterile needles are used.

Related pages

On this site
Tests: HIV antigen/antibody test, p24 antigen
Conditions: Sexually transmitted diseases

Elsewhere on the web
Better Health Channel: Sexually transmitted infections
Healthdirect Australia: Sexually transmitted infections
Australian Federation of AIDS Organisations (AFAO)
National Association of People Living With HIV/AIDS (napwa)
Centers for Disease Control and Prevention (CDC, USA)


1. CDC - HIV basics
2. HIV in Pregnancy. Glenda E Gray and James A McIntyre BMJ 2007;334;950-953 doi:10.1136/bmj.39176.674977.AD
3. National Guidelines for Post-Exposure Prophylaxis after Non-Occupational Exposure to HIV
4. Kitahata, M. N Engl J Med 2009;360:1815-26.
5. Hutter, G. N Engl J Med 2009;360:692-8.