HIV attacks a specific type of immune system cell in the body. It’s known as the CD4 helper cell or T cell. When HIV destroys this cell, it becomes harder for the body to fight off other infections.

When HIV is left untreated, even a minor infection such as a cold can be much more severe. This is because the body has difficulty responding to new infections.

Not only does HIV attack CD4 cells, it also uses the cells to make more of the virus. HIV destroys CD4 cells by using their replication machinery to create new copies of the virus. This ultimately causes the CD4 cells to swell and burst.

When the virus has destroyed a certain number of CD4 cells and the CD4 count drops below 200, a person will have progressed to AIDS.

However, it’s important to note that advancements in HIV treatment have made it possible for many people with HIV to live longer, healthier lives.

HIV is transmitted through contact with the following bodily fluids, from most likely to lead to HIV transmission to least likely:

  • blood
  • semen
  • vaginal fluid
  • breast milk

Sex without a condom and sharing needles — even tattoo or piercing needles — can result in the transmission of HIV. However, if an HIV-positive person is able to achieve viral suppression, then they’ll be unable to transmit HIV to others through sexual contact.

According to the Centers for Disease Control and Prevention (CDC), a person has reached viral suppression when they have fewer than 200 copies of HIV RNA per milliliter of blood.

infographic HIV

HIV is classified into 3 stages: acute HIV, chronic HIV, and AIDS.

HIV doesn’t always multiply rapidly. If left untreated, it can take years for a person’s immune system to be affected enough to show signs of immune dysfunction and other infections. View a timeline of HIV symptoms.

Even without symptoms, HIV can still be present in the body and can still be transmitted. Receiving adequate treatment that results in viral suppression stops the progression of immune dysfunction and AIDS. Adequate treatment also helps a damaged immune system to recover.

Once a person contracts HIV, the acute infection takes place immediately.

Symptoms of the acute infection may take place days to weeks after the virus has been contracted. During this time, the virus is multiplying rapidly in the body, unchecked.

This initial HIV stage can result in flu-like symptoms. Examples of these symptoms include:

However, not all people with HIV experience initial flu-like symptoms.

The flu symptoms are due to the increase of copies of HIV and widespread infection in the body. During this time, the amount of CD4 cells starts to fall very quickly. The immune system then kicks in, causing CD4 levels to rise once again. However, the CD4 levels may not return to their pre-HIV height.

In addition to potentially causing symptoms, the acute stage is when people with HIV have the greatest chance of transmitting the virus to others. This is because HIV levels are very high at this time. The acute stage typically lasts between several weeks and months.

The chronic HIV stage is known as the latent or asymptomatic stage. During this stage, a person usually won’t have as many symptoms as they did during the acute phase. This is because the virus doesn’t multiply as quickly.

However, a person can still transmit HIV if the virus is left untreated and they continue to have a detectable viral load. Without treatment, the chronic HIV stage can last for many years before advancing to AIDS.

Advances in antiretroviral treatments have significantly improved the outlook for people living with HIV. With proper treatment, many people who are HIV-positive are able to achieve viral suppression and live long, healthy lives. Learn more about HIV and life expectancy.

A normal CD4 count ranges from approximately 500 to 1,600 cells per cubic millimeter of blood (cells/mm3) in healthy adults, according to HIV.gov.

A person receives an AIDS diagnosis when they have a CD4 count of fewer than 200 cells/mm3.

A person may also receive an AIDS diagnosis if they’ve had an opportunistic infection or another AIDS-defining condition.

People with AIDS are vulnerable to opportunistic infections and common infections that may include tuberculosis, toxoplasmosis, and pneumonia.

People with weakened immune systems are also more susceptible to certain types of cancer, such as lymphoma and cervical cancer.

The survival rate for people with AIDS varies depending on treatment and other factors.

The most important factor affecting HIV progression is the ability to achieve viral suppression. Taking antiretroviral therapy regularly helps many people slow the progression of HIV and reach viral suppression.

However, a variety of factors affect HIV progression, and some people progress through the phases of HIV more quickly than others.

Factors that affect HIV progression can include:

  • Ability to achieve viral suppression. Whether someone can take their antiretroviral medications and achieve viral suppression is the most important factor by far.
  • Age when symptoms start. Being older can result in faster progression of HIV.
  • Health before treatment. If a person had other diseases, such as tuberculosis, hepatitis C, or other sexually transmitted diseases (STDs), it can affect their overall health.
  • Timing of diagnosis. Another important factor is how soon a person was diagnosed after they contracted HIV. The longer between their diagnosis and treatment, the more time the disease has to progress unchecked.
  • Lifestyle. Practicing an unhealthy lifestyle, such as having a poor diet and experiencing severe stress, can cause HIV to progress more quickly.
  • Genetic history. Some people seem to progress more quickly through their disease given their genetic makeup.

Some factors can delay or slow the progression of HIV. These include:

Living a healthy lifestyle and seeing a healthcare provider regularly can make a big difference in a person’s overall health.

Treatments for HIV typically involve antiretroviral therapy. This isn’t a specific regimen, but instead a combination of three or four drugs. The U.S. Food and Drug Administration has currently approved 40 different medications to treat HIV.

Antiretroviral therapy works to prevent the virus from copying itself. This maintains immunity levels while slowing the progression of HIV.

Before prescribing medication, a healthcare provider will take the following factors into consideration:

There are seven classes of HIV drugs, and a typical treatment regimen involves medications from different classes.

Most healthcare providers will start people with HIV on a combination of three medications from at least two different drug classes. These classes, from the most commonly prescribed to the least commonly prescribed, are:

  • CCR5 antagonists (CCR5s)
  • fusion inhibitors
  • post-attachment inhibitors, a new drug class not in significant use yet

HIV doesn’t cause a lot of outward or noticeable symptoms until the disease has progressed. For this reason, it’s important to understand how HIV is transmitted and the ways to prevent transmission.

HIV can be transmitted by:

  • having sex, including oral, vaginal, and anal sex
  • sharing needles, including tattoo needles, needles used for body piercing, and needles used for injecting drugs
  • coming into contact with body fluids, such as semen, vaginal fluid, blood, and breast milk

HIV is not transmitted by:

  • breathing the same air as a person living with HIV
  • getting bitten by a mosquito or other biting insect
  • hugging, holding hands with, kissing, or touching a person living with HIV
  • touching a door handle or toilet seat that’s been used by an HIV-positive person

Keeping this in mind, some of the ways a person can prevent HIV include:

  • practicing the abstinence method by refraining from oral, anal, or vaginal sex
  • always using a latex barrier, such as a condom, when having oral, anal, or vaginal sex
  • avoiding sharing needles with other people

Healthcare providers usually recommend that people get an HIV test at least once a year if they’ve had sex without condoms or shared needles with anyone in the past. People with past exposure to HIV would also benefit from episodic testing.

If a person has been exposed to HIV within the past 72 hours, they should consider post-exposure prophylaxis, otherwise known as PEP. People with ongoing exposure to HIV may benefit from pre-exposure prophylaxis (PrEP) and regular testing.

Symptoms can take years to appear, which is why it’s so important to get tested regularly.

Advances in HIV treatments mean that people are living longer with the condition than ever before. Getting tested regularly and taking good care of one’s health can reduce transmission.

If HIV is contracted, getting early treatment can prevent further transmission to others as well as progression of the disease. Treatment is vital to prevent the disease from progressing to AIDS.