What Is MAC Lung Disease?

Reviewed by: HU Medical Review Board | Last reviewed: December 2022 | Last updated: December 2022

There are many types of lung disease. Some lung problems are caused by genetic issues like cystic fibrosis. Environmental exposures like cigarette smoke can cause lung disease, too. And certain types of infections can lead to lung damage.1

One group of bacteria that can infect the lungs is called mycobacteria. There are two types of mycobacteria: tuberculosis and nontuberculous. Mycobacterium tuberculosis causes tuberculosis (TB), a very contagious and sometimes deadly lung infection. Nontuberculous mycobacteria can cause lung disease as well, including MAC lung disease.2

What causes MAC lung disease?

Mycobacterium avium complex (MAC) bacteria are a type of nontuberculous mycobacteria (NTM). When a person gets a lung infection from MAC germs, they have MAC lung disease.2-4

MAC germs can be found everywhere. They are in dirt, some food products, and even many water supplies. Humans and some animals also carry MAC germs.2-4

However, MAC lung disease does not spread from person to person or from animal to person. MAC germs can get stirred up into the air from their source (like soil or steam). People can also eat or drink them if they are in food or water.2-4

Who is at risk for MAC lung disease?

You likely have MAC germs in your body right now. People come in contact with them all the time. MAC germs grow slowly, and the immune system is typically strong enough to prevent them from causing a serious infection. But if you have a weakened immune system, it may be easier for MAC lung disease to develop.2-4

People at increased risk of MAC lung disease include:2-4

  • People with HIV
  • People who have a weakened immune system or who take drugs to suppress their immune system
  • People over the age of 65
  • People who smoke
  • People with existing lung issues, like cystic fibrosis or chronic obstructive pulmonary disease (COPD)

What are the symptoms of MAC lung disease?

The symptoms of MAC lung disease can be hard to spot. They vary in each person. It can also be hard to tell if a symptom is related to MAC or a different underlying lung problem, since both can happen at once. Sometimes, there may be no symptoms at all. Symptoms can be absent or very minor for years.2-4

If symptoms are present, they may include:2-4

  • Chronic (long-term) cough, with or without mucus
  • Fatigue or severe tiredness
  • Shortness of breath
  • Weight loss
  • Chest pain
  • Sweating at night
  • Coughing up blood (hemoptysis)
  • Anxiety
  • Fever
  • Weakness

If you have any of these symptoms and are concerned about MAC lung disease, talk with your doctor. Let your doctor know about any other health issues you have or drugs you take so they can best assess your condition.

How is MAC lung disease diagnosed?

Because MAC lung disease symptoms are not specific and can be minor, diagnosis can be tricky. Sometimes, lung damage seen on imaging tests can also be unclear or overlap with other health issues.2,5,6

Also, since MAC germs are everywhere, it can be hard to tell whether you have an active infection. If you test positive for MAC, the test may have been contaminated or you may have inactive MAC germs in your body.2,5,6

Making a MAC lung disease diagnosis often requires the help of a specialist. These doctors include lung doctors (pulmonologists) or infectious disease doctors. They may look at:2,5,6

  • Your symptoms
  • Saliva and mucus (sputum) samples
  • Chest images like X-rays or computed tomography (CT) scans

In some cases, doctors do a bronchoscopy. This involves running a thin tube into your mouth and down your airways to get a sample of fluid from your lungs.2,5,6

How is MAC lung disease treated?

Not everyone with MAC lung disease needs treatment right away. MAC is slow growing, and drugs to treat it can have side effects. If you have no or few symptoms, you may be able to wait on treatment. But even if you wait at first, you will usually need treatment eventually.7

Together, you and your doctor will make the decision of when and how to treat your MAC lung disease. Some factors that may affect treatment planning are:7

  • Your other health conditions
  • Severity of your lung issues
  • Your body weight
  • Your age

MAC is treated with antibiotic drugs. These drugs attack germs like MAC. However, MAC germs have the ability to change (mutate) over time. This can make antibiotic drugs work less well. When this happens, germs are known as antibiotic resistant.2,4,7

To prevent resistant germs, people with MAC might take 2 to 4 different drugs at once. Treatment often lasts 15 to 18 months. Your doctor will monitor you for signs that treatment is working and for drug-related side effects.2,4,7

Surgery may be helpful if drugs do not work or if the MAC infection is limited to one area of the lung. This surgery is called a lung resection.4,7

There also are other ways to help clear mucus and improve health in people with MAC lung disease. These include:4,7

  • Chest physical therapy
  • Controlled coughing
  • Inhalers
  • Vibrating vests to help break up mucus

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