What Is Immune Reconstitution Inflammatory Syndrome?

Immune reconstitution inflammatory syndrome — usually called IRIS — is a paradoxical reaction that happens when the immune system starts recovering and then attacks an infection that was already there. The symptoms are not caused by a new germ. They are caused by the immune system waking up and responding more strongly to something it had been ignoring. IRIS is seen most often in people with advanced HIV who begin antiretroviral therapy, but it can also occur after treatment for tuberculosis, in organ transplant recipients, and in some people starting treatment for certain other infections.

What Is Immune Reconstitution Inflammatory Syndrome?

IRIS is a clinical syndrome defined by a worsening of symptoms or the appearance of new symptoms of an infection or inflammatory condition shortly after the immune system begins to recover. It is most commonly described in people with HIV who start antiretroviral therapy (ART) when their CD4 count is very low.

The key feature is that the reaction is not caused by treatment failure or a new infection. It is caused by a restored immune response that is now able to recognize and react to an infection that was already present but had been poorly controlled because the immune system was too weak to mount a strong response.

IRIS can be broadly divided into two types. In “unmasking” IRIS, the immune recovery reveals a previously undiagnosed infection that was present but not causing obvious symptoms. In “paradoxical” IRIS, a known infection that was being treated gets worse even though the treatment is working.

What Causes IRIS?

The cause is a rapid shift in immune function. When the immune system is severely suppressed — as in advanced HIV — it cannot mount a strong inflammatory response to infections. When treatment restores some immune function, the body suddenly recognizes those infections and responds with inflammation.

This inflammation is what produces the symptoms. The immune system is doing what it is supposed to do, but the response is exaggerated or misdirected relative to the amount of infection present.

Several factors increase the risk of IRIS:

• Very low CD4 count at the time ART is started
• A high viral load
• Starting ART very soon after beginning treatment for an opportunistic infection
• Having a known or undiagnosed infection at the time immune recovery begins
• Rapid improvement in CD4 count after starting ART

IRIS is not a sign that ART is failing. In fact, it usually indicates that the immune system is responding to treatment.

What Are the Symptoms of IRIS?

Symptoms depend on which infection or condition the immune system is reacting to. There is no single set of symptoms that applies to everyone.

Common patterns include:

• Fever that appears or gets worse after starting ART
• Swollen lymph nodes
• Worsening skin lesions or new rashes
• Increased cough, shortness of breath, or chest pain if the lungs are involved
• Headache, confusion, or seizures if the brain is involved
• Abdominal pain or jaundice if the liver is involved

The timing matters. IRIS typically appears within the first few weeks to months after starting ART, though it can occur later. The symptoms often overlap with those of the underlying infection, which makes diagnosis tricky.

Doctors diagnose IRIS by looking at the timing, the clinical picture, and by ruling out other causes such as drug side effects, treatment failure, or a new infection.

Which Infections Are Linked to IRIS?

IRIS has been reported with many different infections. The most common associations include:

• Tuberculosis (TB) — one of the most frequent and serious causes of IRIS, especially in areas where TB is common
• Cryptococcal meningitis — a fungal infection of the brain lining that can cause severe IRIS
• Mycobacterium avium complex (MAC) — a bacterial infection that often affects people with very low CD4 counts
• Cytomegalovirus (CMV) — a virus that can affect the eyes, gut, and other organs
• Pneumocystis jirovecii pneumonia (PCP) — a fungal lung infection
• Herpes simplex and varicella-zoster virus — viruses that cause skin and nerve symptoms
• Hepatitis B and C — liver infections that can flare during immune recovery

IRIS is not limited to HIV. It has been described after treatment for TB in people without HIV, after stem cell transplants, after organ transplants, and in some people recovering from certain infections or stopping immunosuppressive drugs.

How Is IRIS Treated?

Treatment depends on how severe the reaction is and which infection is involved. The approach is individualized.

For mild IRIS, doctors may recommend supportive care — treating symptoms like fever or pain — while continuing ART and infection treatment. The reaction often settles on its own as the immune system adjusts.

For moderate to severe IRIS, anti-inflammatory drugs such as corticosteroids may be used. This is a clinical decision. Corticosteroids can reduce inflammation, but they also suppress the immune system, so they are not appropriate for everyone. Some clinicians use them for specific situations, such as TB IRIS affecting the brain or severe cryptococcal IRIS, but the evidence for benefit varies by infection.

In some cases, doctors may temporarily hold ART. This is uncommon and usually reserved for life-threatening IRIS. The decision to interrupt ART is serious because it can allow HIV to rebound and lead to drug resistance.

Treatment of the underlying infection continues in almost all cases. Stopping infection treatment would not help IRIS and could make the infection worse.

There is no single drug approved specifically for IRIS. Management is based on clinical judgment and the specific infection involved.

Can IRIS Be Prevented?

There is no guaranteed way to prevent IRIS, but certain strategies can reduce the risk or lessen its severity.

For people with HIV, starting ART before the immune system is severely damaged lowers the risk. When ART is started at higher CD4 counts, there is less immune recovery happening at once, and fewer undiagnosed infections are present.

When a person has a known opportunistic infection, doctors sometimes delay ART for a short period to allow infection treatment to take effect first. The timing varies by infection. For example, in cryptococcal meningitis, some guidelines recommend delaying ART by a few weeks. In TB, the timing depends on CD4 count and other factors.

Screening for and treating infections before starting ART can also help. This includes testing for TB, hepatitis, and other common infections in people with advanced HIV.

Even with these measures, IRIS can still occur. It is not always preventable.

What Is the Outlook for People With IRIS?

Most people recover from IRIS. For mild cases, symptoms often resolve within weeks to a few months as the immune system stabilizes.

Severe IRIS can be life-threatening, especially when it involves the brain, lungs, or multiple organs. The risk of death is higher in IRIS related to cryptococcal meningitis and TB, particularly in resource-limited settings.

The long-term outlook is generally good for people who survive the acute episode. Once the immune system reaches a new balance, IRIS does not usually recur. ART is continued, and the underlying infection is treated.

It is important to note that IRIS is not a reason to stop ART. Stopping ART would lead to further immune suppression and worse outcomes.

How Common Is IRIS?

The frequency of IRIS varies widely depending on the population and the infections involved. In people with HIV starting ART, estimates range from about 10% to 25% in some studies, but the numbers vary by setting, CD4 count, and whether an opportunistic infection is present.

IRIS is more common in people with very low CD4 counts (below 100 cells/mm³) and in those with a known opportunistic infection at the time ART is started.

In resource-limited settings where TB and cryptococcal meningitis are more common, IRIS is a significant clinical concern. In settings where ART is started earlier, IRIS is less frequent.

There is no reliable way to predict who will develop IRIS, which is why monitoring after starting ART is important.

What Is the Difference Between IRIS and Treatment Failure?

IRIS and treatment failure can look similar — both involve worsening symptoms after starting treatment. But they have different causes and different responses.

In treatment failure, the infection is getting worse because the treatment is not working. The immune system is not recovering effectively, or the infection is resistant to the drug.

In IRIS, the infection is usually improving or stable, but the immune system is overreacting to it. The treatment is working, but the inflammatory response is causing symptoms.

Doctors distinguish between the two by checking viral loads, CD4 counts, and specific tests for the infection. In IRIS, the HIV viral load typically drops and the CD4 count rises. In treatment failure, those markers do not improve.

This distinction matters because the response is different. In treatment failure, the treatment regimen may need to be changed. In IRIS, the treatment is usually continued, and the focus is on managing inflammation.

What Should You Do If You Think You Have IRIS?

If you are starting ART or treatment for an infection and your symptoms get worse, contact your doctor. Do not stop your medications on your own.

IRIS is a manageable condition, but it needs medical evaluation. Your doctor can determine whether your symptoms are from IRIS, a side effect of medication, a new infection, or treatment failure.

Seek emergency care if you have severe headache, confusion, seizures, difficulty breathing, or chest pain. These can be signs of serious IRIS involving the brain or lungs.

If you have HIV and have not started ART, talk to your doctor about when to start. Earlier treatment reduces the risk of IRIS and improves long-term outcomes.