If your immune system ever got to the point where it was severely damaged by HIV and you developed one or more specific opportunistic infections or tumours, you would be diagnosed with AIDS. For this reason, the specific opportunistic infections or tumours that result in an AIDS diagnosis are known as AIDS defining illnesses.

There’s more information about how HIV can cause opportunistic infections or tumours in the section on How HIV Works.

When you’re reading through this page, remember that HIV treatment these days is very effective in stopping HIV from damaging your immune system to the point where any of these AIDS defining illnesses would be likely to occur. As such, many of these illnesses are now extremely rare in the UK, and so the chances that you’ll get one of them are small. This isn’t to say that they don’t happen; some men don’t discover that they have HIV until they develop symptoms of one or more of these illnesses.

Below are some of the more common AIDS-defining illnesses and information about how to recognise their symptoms. If you think you may be developing symptoms of one or more of these illnesses, especially if you have a CD4 count below 250, it’s important that you go to see your HIV doctor or the on-call doctor at your HIV clinic straight away. Click on the "Read More" button to expand each article.

PCP (pneumocystis carinii pneumonia)
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A fungal form of pneumonia. Common symptoms are fever, shortness of breath, a dry cough and tightness in the lungs. You may also feel generally unwell and experience weight loss and diarrhoea. PCP is a serious and potentially fatal condition so if you have a low CD4 count and symptoms like these develop it’s vital that you see your HIV doctor or an on-call doctor at your clinic as soon as possible.
TB (tuberculosis)
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A bacterial infection of the lungs. Symptoms are shortness of breath, fever, coughing, chest pain and weight loss. TB is a very serious and potentially fatal condition. It is also highly contagious and, as with PCP, if you develop symptoms like these you need to see your HIV doctor or an on-call doctor at your clinic as soon as possible.
KS (Kaposi's sarcoma)
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A type of cancer most commonly seen as bruise-like lesions or patches on the skin, but can also affect internal organs such as your lungs especially if you have a low CD4 count. If you develop dark patches or lesions on your skin you should get your HIV doctor to check them out.
Candidiasis (thrush)
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A fungus that can affect the mouth, throat and penis. Depending on the severity and location of the infection, symptoms of candidiasis can include white blobs in the mouth and throat, red patches in the mouth, white or red cracks at the corners of the mouth, chest pain and difficulty swallowing. If it affects the penis you may experience pain under the foreskin. If you develop any of these symptoms get your HIV doctor to check them out.
CMV (cytomegalovirus)
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A virus that can affect different parts of the body in different ways, such as the eyes, gut, lungs and nervous system. It can cause CMV retinitis with symptoms including seeing floating spots, blurred vision and blind spots leading to permanent damage and even loss of vision. Symptoms of gastrointestinal CMV infection include diarrhoea, fever, abdominal pain and weight loss. CMV can also affect the lungs causing pneumonia like symptoms, and also the nervous system causing pain, numbness and weakness in the peripheral nerves. It can also affect the brain and spinal cord causing swelling of the brain, loss of feeling in the limbs. CMV is a very serious condition and so you should see your HIV doctor as soon as possible if any of these symptoms develop.
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A parasite causing cysts to form on the brain. Symptoms at first include headache, fever, tiredness and confusion. This can progress to fits, strokes, difficulty speaking and personality changes. You should see your HIV doctor as soon as possible if you develop any of these symptoms as left untreated toxoplasmosis can lead to coma and death.
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A low platelet count (the clotting cells in your blood) causing bruising and internal bleeding. Symptoms include skin that bruises easily, coughing up blood or blood in your shit. If you notice these symptoms developing get your HIV doctor to check them out.
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A cancer of the lymphatic system (lymph glands and white blood cells) that can spread around the body. The most common form in people with HIV is Non-Hodgkin’s Lymphoma (NHL). Symptoms include fever, severe night sweats, swollen lymph glands and weight loss. If it affects the nervous system it can cause headaches, confusion, memory loss and partial paralysis of one side of the body. As with all cancers, the earlier a lymphoma is diagnosed the more chance there is of survival, so seeing your HIV doctor as soon as possible if you develop these symptoms is vital.
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A sometimes known as AIDS-related dementia and caused by the effect of HIV on the central nervous system. Symptoms of dementia can include loss of memory, forgetfulness, confusion, changes in behaviour and loss of motor control. See your HIV doctor if you develop symptoms such as these.
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A parasite which lives in the bowel and gut. Symptoms include diarrhoea, cramping pain in the abdomen, loss of appetite, weight loss, nausea, vomiting, excessive wind, liver inflammation and jaundice. See your HIV doctor if you develop these symptoms.
Cryptococcal meningitis
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A fungus causing inflammation of the membranes around the spinal cord and brain. Symptoms can include fever, headache, stiff neck, confusion, nausea, weight loss. It can also lead to strokes and coma. If these symptoms develop see your HIV doctor as soon as possible.
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A bacterial infection with symptoms including severe anaemia, weight loss, high fever, diarrhoea, night sweats and weakness. Other symptoms can include abdominal pain enlarged lymph nodes, liver and spleen. See your HIV doctor as soon as possible if these symptoms develop.