Acute and primary HIV infection

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Key points

  • Early HIV infection may cause flu-like symptoms.
  • Some tests are better able to detect HIV after a recent infection than others.
  • HIV multiplies quickly during the early phase and weakens the immune system.
  • Starting treatment soon after diagnosis prevents infecting others and protects the immune system.

Acute HIV infection is the immediate period after HIV infection and refers to the first month after you have been infected, while the term primary HIV infection is the six-month period after infection. This early period represents an important time in terms of infectiousness and damage to the immune system.

Seroconversion symptoms

After being infected with HIV, you might feel unwell for a short time. Symptoms of early HIV infection may include non-specific, flu-like symptoms, such as: fever, swollen glands, a sore throat, oral ulcers or thrush, weight loss, tiredness, body aches, vomiting and a rash. This is called seroconversion illness and usually occurs one to four weeks after infection. Symptomatic seroconversion illness occurs in at least 50%, and possibly as many as 80 or 90%, of infected individuals.

During seroconversion, your immune system is weakened and HIV spreads very quickly throughout your body. The strength of the immune system is measured by looking at CD4 cells; these cell counts usually drop during this early phase of infection. There is a high amount of HIV in your blood and this is known as the viral load. In this early phase of infection, there is more risk of infecting others due to a high viral load.

HIV testing after a recent infection

If you are concerned about a possible recent HIV infection, you should take an HIV test. If this test result is non-reactive or negative, it can be repeated in a few weeks to be sure. Not everyone has symptoms after a recent infection and thus testing is the only reliable way to know whether you have HIV.

If you might have been exposed to HIV within the last 72 hours, you and your doctor should also discuss whether post-exposure prophylaxis (PEP) is appropriate in your case. PEP is taken in order to prevent HIV from taking hold and to remain HIV negative.

The most accurate tests for HIV diagnosis after recent infection are antigen/antibody laboratory tests (also known as fourth-generation or ELISA tests). An HIV antigen is part of the virus itself and is present in high levels in the blood between HIV infection and seroconversion. During seroconversion, HIV antibodies are produced by the body in response to infection and they persist for life.

"Symptomatic seroconversion illness occurs in at least 50%, and possibly as many as 80 or 90%, of infected individuals."

HIV antigen/antibody tests will detect the majority of those infected with HIV within four weeks of infection but can sometimes detect infections as early as ten days afterward. While they are extremely accurate, they require blood to be drawn with a needle and results are not available immediately. These tests tend to be offered in hospital settings or for confirmatory purposes.

Rapid, point-of-care tests can be administered and interpreted in any setting, requiring only a tiny sample of blood (obtained via a finger prick) or oral fluid (obtained via a mouth swab), with a result usually available within 30 minutes. Similarly, self-tests can be carried out at home, where you administer the test yourself and interpret the results based on the instructions provided. The downside to both these types of tests is that they might not be able to accurately detect a recent infection. Most rely on detecting HIV antibodies, which may take some time to appear.

Thus, it is advisable to test using a laboratory test which is able to test for both HIV antigen and antibodies.

Point-of-care and self-tests can sometimes give false negative test results to people who start antiretroviral therapy (ART) very soon after HIV infection. It appears that when treatment is started during acute infection, the antibody response may be suppressed. This could lead to a negative test result but does not mean that HIV has been cured or removed from the body. If you are already taking HIV treatment, you should not use a rapid test or self-test to confirm that you have HIV.

Starting treatment

Current treatment guidelines in the UK suggest that all people with a recent HIV infection are reviewed by a specialist and offered ART immediately. Treatment should be started when you feel ready to do so.

However, there are some instances in acute or primary infection when treatment is strongly recommended, including:

  • Neurological symptoms (meningitis, cognitive or motor symptoms, weakness/numbness as a result of nerve damage)
  • Any AIDS-defining illness
  • A CD4 count below 350 cells
  • If you had an HIV-negative test result within 12 weeks of being diagnosed with HIV.

There are benefits to starting treatment as soon as possible, regardless of CD4 count. One benefit is preventing onward transmission of HIV. After starting treatment, your viral load will drop until it reaches a low enough level to be classified as ‘undetectable’. Research shows that those on effective treatment with an undetectable viral load cannot transmit the virus to others. It may take a few months to reduce the viral load to undetectable levels once on treatment.

Prior to starting treatment, you are most infectious during early HIV infection when the viral load is very high. It is important that preventative methods such as condoms or PrEP are used during this time to protect sexual partners.


immune system

The body's mechanisms for fighting infections and eradicating dysfunctional cells.

viral load

Measurement of the amount of virus in a blood sample, reported as number of HIV RNA copies per milliliter of blood plasma. Viral load is an important indicator of HIV progression and of how well treatment is working. 



Any perceptible, subjective change in the body or its functions that signals the presence of a disease or condition, as reported by the patient.



The transition period from infection with HIV to the detectable presence of HIV antibodies in the blood. When seroconversion occurs (usually within a few weeks of infection), the result of an HIV antibody test changes from HIV negative to HIV positive. Seroconversion may be accompanied with flu-like symptoms.


undetectable viral load

A level of viral load that is too low to be picked up by the particular viral load test being used or below an agreed threshold (such as 50 copies/ml or 200 copies/ml). An undetectable viral load is the first goal of antiretroviral therapy.

Going on treatment ensures that the amount of virus in the body can be kept undetectable and that your immune system is given a chance to strengthen in order to prevent illnesses. If you start treatment during the early stage of infection, this will help limit damage to the immune system. There is evidence that there is less chance of achieving a normal CD4 cell count if treatment is delayed for more than a year after infection. Thus, starting treatment within a year, if not sooner, is advised.

Starting treatment remains your decision and you should discuss any concerns you have with your doctor. Maintaining adherence to treatment in order to achieve a very low (undetectable) viral load is important in order to get the virus under control and limit its ability to damage your immune system. Taking medication will be an ongoing and long-term commitment.

Even if you do not take treatment, after a few months, your immune system will be better at keeping the virus under control. You will feel better, your viral load will go down and your CD4 count will go up. Nonetheless, you could still pass on HIV if you are not taking treatment.

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