Acute HIV: Symptoms, Diagnosis, and Treatment

Acute HIV infection, also called primary HIV infection or acute retroviral syndrome, is the first stage of infection with the human immunodeficiency virus. This initial phase develops within two to four weeks after exposure. During this period, the virus multiplies rapidly, spreading throughout the body. This replication leads to very high levels of the virus in the bloodstream and a corresponding drop in infection-fighting CD4 cells, a type of lymphocyte in the immune system.

Common Symptoms of Acute HIV Infection

The symptoms associated with acute HIV infection are often non-specific and can be mistaken for other common viral illnesses, such as influenza or mononucleosis. Many individuals experience flu-like symptoms that can include fever, headache, fatigue, and a sore throat. Other common signs are swollen lymph nodes, muscle and joint pain, and the appearance of a rash. The rash consists of small, discolored, flat blemishes that are not itchy.

Some people may also experience night sweats, diarrhea, or mouth ulcers. The severity of these symptoms can vary widely among individuals, with some people having very mild symptoms and others experiencing a more significant illness. It is estimated that between 50% and 90% of people will experience some symptoms during this stage. Because these signs are not unique to HIV, specific testing is required for a diagnosis.

How Acute HIV is Diagnosed

Diagnosing HIV during the acute phase presents challenges due to the “window period.” This is the time after infection occurs but before the body has developed a detectable level of antibodies, which are the target of many standard HIV tests. As a result, a conventional antibody-only test might produce a negative result even when a person is infected and highly infectious.

To overcome this diagnostic hurdle, healthcare providers use tests that can detect the virus itself or its components. One such test is the nucleic acid amplification test (NAAT), which identifies the genetic material (RNA) of the virus in the blood and can detect HIV as early as 10 to 12 days after exposure. Another diagnostic tool is a test that screens for the p24 antigen, a protein that is part of the virus and appears in the bloodstream before antibodies do.

Modern testing strategies often employ fourth-generation combination tests that can detect both HIV antibodies and the p24 antigen simultaneously. This allows for earlier detection than antibody-only tests. If a fourth-generation test is positive, it is followed by additional tests to confirm the diagnosis and differentiate between HIV-1 and HIV-2. Anyone who suspects a recent exposure should seek medical evaluation to ensure the appropriate tests are administered.

Increased Transmission Risk with Acute HIV

The risk of transmitting HIV to another person is elevated during the acute infection stage. This heightened transmissibility is a direct result of the extremely high viral load—the amount of HIV circulating in the blood. This leads to concentrations of the virus in blood and genital secretions that can be many times higher than during the later, chronic stage of infection.

Studies suggest that the probability of transmission per sexual act can be up to 26 times greater during acute HIV infection compared to chronic infection. A person’s viral load is a primary determinant of their infectiousness. The risk is compounded by the fact that many individuals are unaware they have been infected, as the non-specific, flu-like symptoms are often dismissed or misdiagnosed.

Treatment Options During the Acute Phase

Current medical guidelines recommend the immediate initiation of antiretroviral therapy (ART) upon diagnosis of acute HIV infection. Starting treatment as early as possible offers benefits for both individual health and public health. A primary goal of early ART is to quickly lower the high viral load that characterizes the acute phase, which can lessen the severity and duration of symptoms.

Early intervention also has long-term advantages for the immune system. By suppressing the virus, early ART helps preserve the function of CD4 cells and may reduce the size of the latent viral reservoir. This reservoir consists of resting immune cells infected with HIV, and a smaller reservoir is associated with better long-term health outcomes. Starting treatment promptly also dramatically reduces the risk of transmitting the virus to others, and successful ART requires consistent adherence to the prescribed medication.

Progression from Acute to Chronic HIV

If acute HIV infection is not treated, the body’s immune system will eventually bring the period of rapid viral replication under partial control. Following the resolution of the initial symptoms, the infection transitions into its second stage, known as chronic HIV infection or the clinical latency period. During this phase, a person may have few or no symptoms for many years.

Despite the absence of symptoms, the virus is still active and continues to replicate at lower levels, steadily damaging the immune system. After the acute phase, the viral load stabilizes at a level known as the viral set point. This set point is predictive of the long-term prognosis if the infection is left untreated; a higher viral set point is associated with a faster progression to Acquired Immunodeficiency Syndrome (AIDS). Without ART, the chronic stage can last for a decade or more, but for some, it may advance more quickly.