MAC Lung Disease

Bacteria in soil and water cause MAC lung disease in older people or those with weak immune systems or respiratory problems. Most people need several different antibiotics for more than a year to get rid of the infection. MAC lung disease is a type of nontuberculous mycobacterial infection. Unlike tuberculosis (TB), it’s not contagious.


What is MAC lung disease?

A group of bacteria called Mycobacterium avium complex (MAC) causes MAC lung disease. Most people who breathe in or swallow these germs don’t get sick. But some pre-existing conditions can make some people more susceptible to developing a slow-growing infection once MAC enters their airway. When an infection happens, it affects breathing and can be difficult to treat if detected late. MAC lung disease isn’t contagious.


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What is MAC?

MAC bacteria reside naturally in dust, soil and water. They’re a type of nontuberculous mycobacteria (NTM). This category of microbe causes nontuberculous mycobacteria (NTM) infection. There are nearly 200 species of NTM, and MAC accounts for almost 80% of pulmonary diseases in the U.S.

An NTM infection is different from tuberculosis (TB), which is an infectious disease that spreads from person to person and can cause more rapid and severe illness. The Mycobacterium tuberculosis bacterium causes TB.

Many species of mycobacteria comprise the group we call MAC. But the treatment and approach are the same.

How common is MAC lung disease?


More than 86,000 Americans have some type of NTM infection. MAC lung disease is the most common, making up nearly 80% of NTM infections. The amount of NTM lung disease has been steadily growing over the last two decades and experts expect this trend to continue.

What are the types of MAC infections?

MAC infections include:

  • Pulmonary MAC infections affect your lungs and respiratory system.
  • Disseminated MAC infections spread throughout your body through your bloodstream and most commonly affect people with advanced AIDS and other types of immunocompromised conditions.
  • MAC-associated lymphadenitis mainly affects healthy children. It causes swollen lymph nodes, usually in the neck.

What are the types of MAC lung diseases?

There are two types of MAC lung disease:

  • Nodular bronchiectatic. This occurs when infection develops in the small airways and air sacs, causing what looks like lung nodules on imaging. These nodules grow slowly. The chronic inflammation from a slow-growing infection leads to bronchiectasis — an irreversible dilation of the airways that can make it both harder to clear infections and increase the risk of new infections. This type is seen more in older, thin women who don’t smoke. Untreated patients can see an increase in bronchitis and pneumonia.
  • Fibrocavitary disease. This is the more severe form of MAC lung disease. It requires more immediate treatment. When infection causes a hole in your lung tissue, you have a more profound infection and curing it can be more challenging. It’s seen more commonly in people who smoke or have emphysema.

Symptoms and Causes

What causes MAC lung disease?

MAC bacteria naturally reside in soil and water. Stirring up soil or dust can make the bacteria airborne, and you may breathe them in. People who garden or work with soil have slightly more MAC than those who don’t. MAC is also in water, including the water in your home. Chlorinating water, using disinfectants and, in some cases, heating water won’t kill this bacteria efficiently. That may sound alarming, but for most people, the bacteria are harmless. We’re all exposed to NTM every day and most of us never develop an infection.

In a small number of people who have certain predisposing risk factors, the bacteria settle in their lungs and grow slowly, often over many years. The resulting MAC lung infection causes low-grade inflammation and progressive irreversible changes to the airways, until diagnosis and treatment.

What are the risk factors for MAC lung disease?

MAC lung disease affects all ages and genders. People over 65 and women who have gone through menopause are most at risk.

You’re also more likely to get MAC lung disease if you smoke, have a weakened immune system or have a lung condition, such as:

What are MAC lung disease symptoms?

MAC lung disease symptoms vary and often are nonspecific, contributing to delay in diagnosis. Some people have mild or unnoticeable symptoms. Often symptoms aren’t even respiratory in nature. When symptoms occur, you may experience:

Diagnosis and Tests

How is MAC lung disease diagnosed?

Your healthcare provider will perform a physical exam and ask about symptoms.

Tests for MAC lung disease include:

  • Chest X-rays and especially CT scans allow the detection of the lung changes seen with infection.
  • Sputum cultures (lung excretions) to see if MAC grows repeatedly. Since most of us are exposed to MAC bacteria daily, you may get this test more than once on different days to increase the confidence that the bacteria are actually coming from your lungs.
  • Bronchoscopy is essentially like a colonoscopy but for your lungs (with a different, smaller scope). This is reserved for settings where sputum cultures are unable to produce a diagnosis.

Management and Treatment

What are MAC lung disease treatments?

Because MAC lung disease is difficult to get rid of, you may see an infectious disease or a pulmonary specialist. Both specialties have expertise in diagnosing and treating infections.

Treatments for MAC lung disease depend on the severity of symptoms. They include:

  • Watchful waiting. People with minimal symptoms and minimal radiographic changes may not need treatment with antibiotics initially. You’ll have regular follow up with breathing tests and sputum cultures.
  • Airway clearance. This is a group of therapies that help your lungs clear the sputum (and bacteria it holds) from the diseased airways, most often used for bronchiectasis. They include different breathing treatments through a nebulizer and the use of some devices that help move sputum out of the lower airways.
  • Medications: If airway clearance alone is not enough, your provider may prescribe antibiotics. The decision to treat is one that should be made based on many variables after a shared decision-making discussion with your specialist. Bacteria can develop antibiotic resistance, which means the drugs can’t kill them. To help lower the risk of antibiotic resistance while effectively killing the bacteria, you’ll take three different antibiotics for 12 to 18 months. The U.S. Food and Drug Administration (FDA) has recently approved one inhaled antibiotic for people whose infection doesn’t respond to other antibiotics within six months.
  • Surgery: In rare instances, you may need surgery to remove a section of the infected lung if antibiotics fail. After surgery, you’ll take antibiotics for a short while to kill lingering bacteria.

How can you manage MAC lung disease?

These actions can ease MAC lung disease symptoms:

  • Find ways to clear mucus out of the airways. Options include at least 150 minutes per week of moderate-intensity exercise (especially enrolling in pulmonary rehab if you qualify), education from respiratory therapists that focuses on the chest and breathing techniques, controlled coughing, postural drainage (positions to drain mucus out of the lungs) and chest percussions to shake mucus loose.
  • Get help to quit smoking, and avoid second-hand smoke and other lung irritants.
  • Get vaccinated to lower your risk of additional respiratory illnesses like the flu, pneumonia and COVID-19.
  • Maintain a healthy weight through a nutritious diet. Most centers have dieticians that can assist in settings where slow infections like MAC impair nutrition.

What are the complications of MAC lung disease?

Long-term antibiotic use can increase your risk of developing antibiotic resistance. You may also have medication side effects like nausea, diarrhea and abdominal pain. Each antibiotic has specific side effects to watch out for so a discussion with your provider will be important.

Older people who take antibiotics for a long time are at risk for developing Clostridioides difficile (C. diff). This bacterial infection occurs when antibiotics kill good bacteria in the gut that aid digestion. C. diff. affects the digestive system and causes severe, chronic diarrhea. It can be life-threatening.

Severe MAC lung disease can affect your ability to do the things you once loved. As a result, you may develop depression or anxiety.


How can I reduce my risk of MAC lung disease?

These steps may lower your risk of exposure to MAC bacteria:

  • Avoid hot tubs and saunas that recirculate hot, steamy water if your provider feels they may have been the source of your MAC bacteria.
  • Run the vent system in your bathroom and kitchen to clear out steam.
  • Set your home’s hot water heater to at least 130 F (54.4 C).
  • Wear a dust mask when working in the yard or garden.
  • Moisten potting soil before working with it to reduce dust.
  • Stay compliant with an aggressive airway clearance regimen.

Outlook / Prognosis

Can MAC lung disease be cured?

Providers consider MAC lung disease to be cured if sputum cultures show no evidence of infection for 12 months. But the infection can come back, either from a new exposure or lingering bacteria in the lungs, especially since the condition that made you susceptible to MAC is still present.

Your provider will monitor you for signs of reinfection. Lung damage from MAC lung disease is irreversible. You may always have respiratory problems, even after treatment, so the goals and expectations should be clear going into treatment.

Living With

What should I ask my provider?

You may want to ask your healthcare provider:

  • What caused MAC lung disease?
  • What type of MAC lung disease do I have?
  • Do I need treatment?
  • What are my treatment options?
  • Is surgery right for me?
  • What are the risks of surgery?
  • Are there steps I can take at home to improve my breathing?
  • How can I prevent future MAC lung infections?

Additional Common Questions

Is MAC lung disease contagious?

While you can’t catch a MAC infection from someone else, the condition sometimes affects more than one family member. Experts believe certain people have a genetic change (mutation) that makes them more susceptible to MAC infections.

Is MAC lung disease fatal?

In some people, MAC lung disease can cause respiratory failure and death, but this generally happens over a long period of time. Approximately 1 in 4 people with weakened immune systems who develop the cavitary type of MAC lung disease die within five years of the initial MAC lung disease diagnosis. Earlier detection and treatment drastically minimize the long term risks.

A note from Cleveland Clinic

Most people don’t get sick from MAC bacteria. For those who become ill, MAC lung disease can cause serious, sometimes life-threatening, respiratory problems. You should contact your healthcare provider if you cough up blood or experience chronic coughing and extreme fatigue. People with weakened immune systems or other lung conditions are especially vulnerable to MAC lung disease. Antibiotics can treat MAC lung disease, but you may need to take medicine for more than a year.

Medically Reviewed

Last reviewed by a Cleveland Clinic medical professional on 12/01/2021.

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