Updated September 2019


Human Immunodeficiency Virus (HIV) is a virus that attacks the immune system by destroying white blood cells (CD4 and T lymphocytes), which protect the body from infections. HIV is the causative agent of acquired immunodeficiency syndrome (AIDS).


HIV is transmitted through specific exposure to blood and/or body fluids from a person infected with HIV. The most common types of exposure include:

  • Sexual exposure by having unprotected vaginal, anal or oral sex with a person who is infected, especially when there is an untreated infection like syphilis.
  • Blood exposure through intravenous drug use by sharing infected needles, works or other drug use equipment.
  • Mother-to-child transmission from an infected mother to the fetus while in the uterus, from an infected mother to the baby during delivery (more common) or from an infected mother to the baby during breastfeeding.
  • Receiving infected blood or blood products (now rare in Canada).

Signs and Symptoms

A person with HIV may experience several stages.

Primary or acute HIV infection

This is the period from initial infection to the development of antibodies. Although some people have no symptoms in this stage, up to 90 per cent of people have symptoms, including flu-like symptoms, a rash, fever or swollen glands. Symptoms generally appear two to four weeks after the initial infection and are often mild, usually lasting one to two weeks, but may last several months.

Chronic asymptomatic HIV infection

This is the stage where there is a balance between the HIV infection and the immune system response, represented by the levels of CD4 and T lymphocyte cells. Many people fall into this category. Swollen or enlarged lymph nodes are commonly present, along with a low number of red blood cells called platelets.

Chronic symptomatic HIV infection

This is the stage where the HIV virus reproduces and depletes the CD4 and T lymphocyte cells, leaving the immune system compromised. Symptoms may include, fatigue, unexplained weight loss (more than 10 per cent of body weight, chronic diarrhea (more than three weeks), unexplained fever (more than two weeks), or recurrent or chronic yeast infections (oral, esophageal or vaginal).

Diagnosis and Tests

Diagnosis is based on a blood test which checks for antibodies to HIV. This test is most accurate three months after infection. Any doctor or qualified health care provider can order an HIV test. There are three options for testing:

  • Nominal testing: the HIV test is ordered using the name of the person being tested.
  • Non-nominal testing: the HIV test is ordered using a code or the initials of the person being tested. Only the person ordering the test knows the identity of the person being tested and is able to link the result to that person’s health care record.
  • Anonymous testing: the HIV test is ordered using a unique non-identifying code. The person ordering the test and providing the result do not know the identity of the person being tested. Only the person being tested knows the code, so the test result is not linked to that person’s health care record.

It usually takes two weeks to get the results from testing. However, a number of clinics also offer a point-of-care rapid test, which is a finger prick test that gives the results in a few minutes.

Testing is recommended when an individual has high-risk behaviours (multiple sexual partners, unprotected sexual activity, sex with an HIV-infected partner, receptive anal/vaginal intercourse, sharing of intravenous drug equipment or has another sexually transmitted infection, such as syphilis or hepatitis B).


HIV infected persons are at increased risk of opportunistic infections, depending on their CD4 count. Infections can include a number of AIDS-defining conditions, including bacterial, viral, parasitic and fungal infections. The median time from acquiring HIV to the diagnosis of AIDS is well over 10 years.


While there is no cure for HIV, anti-retroviral treatment can help protect the immune system. Current evidence shows that people living with HIV who are taking treatment as prescribed by their health care provider can now live longer and healthier lives. Additionally, those who are able to achieve an undetectable viral load through consistent and effective treatment cannot pass the virus on to their sexual partners.

Treatment of HIV is an increasingly complex area, with changes in optimal therapy occurring as new research becomes available. Guiding principles of treatment include:

  • Treatment is recommended for everyone no matter how long someone has been infected with the virus or how healthy they are.
  • Adherence to treatment is very important. Stick to your pill taking schedule every day.
  • Routine monitoring of CD4 count and HIV viral load are key in assessing the effectiveness of anti-retroviral therapy.

Therapy should be individualized and based on factors such as efficacy, tolerability, potential adverse effects, convenience, and drug interactions.

Prevention/Self-care Tips

Persons with risk behaviours for HIV should complete testing for other sexually transmitted infections (STIs), including chlamydia, gonorrhea, syphilis, Hepatitis A, Hepatitis B and Hepatitis C, as sexual transmission of HIV is enhanced by the presence of other STIs. If an individual does not have immunity to Hepatitis A or B, vaccination should be discussed.

It is important to remember to use condoms correctly every time you have sex to lower your chance of getting HIV and other sexually transmitted infections.

Oral pre-exposure prophylaxis (PrEP)

Oral PrEP is a way for an HIV-negative person who is at risk of HIV infection to reduce their risk of getting HIV by taking antiretroviral drugs. When taken as prescribed, PrEP medication reduces the risk of acquiring sexually transmitted HIV by more than 90 per cent. For more information on PrEP and where to access it please visit PrEP (Ontario HIV Treatment Network).

Post-exposure prophylaxis (PEP)

PEP is used to help prevent the acquisition of HIV infection by individuals who may have been recently exposed to HIV. PEP is effective when taken within 72 hours of suspected high-risk exposure to HIV. It involves antiretroviral medications taken once daily for four weeks (28 days). In Toronto, PEP is usually accessed through the Emergency Department of the hospital. For more information on PEP please visit Post-exposure prophylaxis (PEP) (CATIE).

Information for Sexual Partners

All of your sexual partners within the past 90 days prior to your last negative HIV test should be notified so that they can be tested. If you have never been tested for HIV, all of your sexual partners will need to be notified to get tested.

If you do not want to tell your partner(s), a public health nurse can notify them for you. Your name will be kept confidential.

More Information

Call the Sexual Health Infoline Ontario at 416-392-2437 or 1-800-668-2437.

Safer sex: To reduce your risk of getting a sexually transmitted infection (STI), use a condom every time you have vaginal, anal or oral sex.