What Is MAC Lung Disease?

Mycobacterium Avium Complex (MAC) is a group of environmental bacteria that are not harmful to most people, however, for those with weakened immune systems and/or respiratory problems, it can cause MAC lung disease. MAC lung disease reduces the lung's functionality, causing fatigue, shortness of breath, coughing up blood, weight loss, and more.

MAC lung disease is a bacterial lung infection resulting from exposure to the Mycobacterium Avium Complex (MAC) group.

  • The MAC group of bacteria includes the species M. avium and M. intracellulare, they are not spread from person to person but are commonly found in dust, soil, and water. 
  • For most, MAC bacteria are harmless; however, for those with certain risk factors a MAC infection can be extremely serious. 
  • MAC lung diseases primarily affect those who have weak immune systems, or pre-existing respiratory problems. 

If discovered early, it can be treated through a course of antibiotics.1

Clinical outcomes vary for the type of MAC lung disease and when treatment begins. When caught early as many as 88% of patients can have favorable outcomes with antibiotics1, therefore understanding the disease is important in the fight against it.


MAC lung disease is a nontuberculous mycobacterial (NTM) infection (meaning mycobacterial infection that is not tuberculosis) of the lung tissue that can cause dilation of the lungs or rupture the lung tissue.1 Environmental species of MAC mycobacteria enter the lungs through inhalation or swallowing, which can cause a lung infection. Those with pre-existing immune disorders, underlying lung conditions, smokers, those over age 65, and postmenopausal assigned females at birth (AFAB) are the most at risk.1 MAC lung can be treated with antibiotics in the majority of cases, but other treatment options are available.1

Types of MAC lung infection and disease

MAC bacteria are a type of NTM that cause infection. Pulmonary MAC infections affect the lungs and the respiratory system leading to MAC lung disease.  In the lungs, MAC bacteria can either infect the narrow airways and air sacs in a condition known as a nodular bronchiectasis (NB) infection, or the infection can cause ruptures  in the tissue of the lungs known as fibrocavitary disease3. There are huge differences between the two types of MAC lung disease.

NB Mac infection: a slow-growing infection that causes chronic inflammation in the airways, which then causes dilation in the lungs. This dilation is irreversible and makes it harder for the body to fight infections in the lungs, leading to more inflammation. Antibiotics aren’t always needed to treat NB MAC lung disease, but it is vital that doctors monitor the condition in case it gets worse.2

Fibrocavitary disease: a much more serious infection requiring immediate treatment.  Ruptures occur in the lung tissue and if left untreated can lead to failure of the lungs. It is much more common in those with pre-existing lung complications such as emphysema and COPD.1

Causes of MAC lung disease

MAC lung disease is not contagious, as the MAC bacteria cannot spread from one person to another. Environmental MAC species are found in dust, water, and dirt, so can be inhaled or swallowed leading to a pulmonary infection. MAC lung disease is much less common than the MAC bacteria because typical healthy immune systems and/or healthy lungs are able to deal with the bacteria. See risk factors for more on who is at risk.

Risk factors

A weakened immune system and damage to the lung are two predominant risk factors. But there are others. 

Risk factors include:

  • Being 65 and over. 
  • People who have gone through the menopause.
  • AIDS.
  • A weakened immune system.
  • Smoking. 
  • Pre-existing lung complications.

Overall, MAC bacteria can be swallowed or inhaled, but MAC lung disease usually occurs in people with an increased risk due to age or a pre-existing lung/immune condition.1

Signs and symptoms of MAC lung disease

Because MAC lung disease is an infection of the lungs most, but not all symptoms are typical of lung disease or bacterial infection. Signs and symptoms include:

  • Chronic cough and coughing up blood.
  • Shortness of breath.
  • Fatigue. 
  • Night sweats.
  • Weight loss

Management and treatment for MAC lung disease

Treatment options vary depending on the type of MAC lung disease. 

  • Monitoring: for less serious NB MAC infections, a doctor might monitor the progress of the disease. However, this is not an option for fibrocavitary diseases. 
  • Antibiotics: A doctor will prescribe antibiotics for more serious infections. This includes a therapy of antibiotics for 12 - 18 months.1

Surgery is another option that is often used alongside antibiotics in more serious cases.3


MAC lung disease is diagnosed through a combination of physical examination, imaging tests, and laboratory tests. 

  • Physical examination: initial tests look for physical signs of the disease. 
  • Imaging tests: CT Scans and X-rays of the lungs to test for differences. 
  • Laboratory tests: traditionally sputum cultures are tested for MAC growth. However, MAC can also be found in your blood, bone marrow, and lymph nodes.3 


Antibiotics are not always effective against all types of MAC lung infections. The two main complications that can occur during treatments are antibiotic resistance and recurrent infections from the same MAC bacteria or a different type of NTM bacteria. Early diagnosis of the MAC infection is important for avoiding these complications.1 


How can I prevent MAC lung disease?

Most MAC lung disease risk factors are out of an individual's control. This includes age and pre-existing immune and/or pulmonary conditions. Maintaining healthy lungs is important, so avoiding smoking is one way you can lower the risk in the long term. 

How common is MAC lung disease

MAC lung disease is not very common and is extremely rare in those under the age of 65 without underlying lung and/or immune issues. Overall, NTM infections occur in every 7.8 in 100,000 people, with MAC lung being the most common type comprising 80% of NTM infections, meaning that MAC lung disease occurs in roughly every 6.2 in 100,000 people.

What can I expect if I have MAC lung disease?

What to expect varies with the type of MAC lung disease you have. Antibiotic therapy is common and has positive outcomes in the majority of MAC lung disease patients.1 

Is MAC lung disease contagious?

MAC lung disease is not contagious, as MAC bacteria cannot spread from person to person.2 

When should I see a doctor?

If you have concerns please see a doctor immediately as the sooner it is diagnosed the better the prognosis can be.2 Common symptoms include a persistent cough, coughing up blood, night sweats, and weight loss. 


In summary, MAC lung disease is a type of NTM lung infection that is common in those with underlying immune/pulmonary system conditions. Other risk factors include being over 65 and being post-menopausal. Treatment options, symptoms, and outcomes vary depending on the type of MAC lung disease. However, getting an early diagnosis and medical intervention is key for a good prognosis.


  1. Koh WJ, Moon SM, Kim SY, Woo MA, Kim S, Jhun BW, et al. Outcomes of Mycobacterium avium complex lung disease based on clinical phenotype. European Respiratory Journal [Internet]. 2017 Sep 1 [cited 2023 Oct 13];50(3). Available from: https://erj.ersjournals.com/content/50/3/1602503
  2. Lee G, Lee KS, Moon JW, Koh WJ, Jeong BH, Jeong YJ, et al. Nodular bronchiectatic mycobacterium avium complex pulmonary disease. Natural course on serial computed tomographic scans. Annals ATS [Internet]. 2013 Aug [cited 2023 Oct 13];10(4):299–306. Available from: https://www.atsjournals.org/doi/10.1513/AnnalsATS.201303-062OC
  3. Griffith DE, Aksamit TR. Managing mycobacterium avium complex lung disease with a little help from my friend. Chest [Internet]. 2021 Apr 1 [cited 2023 Oct 13];159(4):1372–81. Available from: https://www.sciencedirect.com/science/article/pii/S0012369220349242
  4. Non-tuberculous mycobacterial infection (Ntm) | Asthma + Lung UK [Internet]. 2022 [cited 2023 Oct 13]. Available from: https://www.asthmaandlung.org.uk/conditions/non-tuberculous-mycobacterial-infection-ntm
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Matthew Gimbert

MSc, Biomedical Science, The University of Sheffield

Matthew has attained a combination of strong practical laboratory skills and in-depth knowledge in a range Biomedical Science topics through his time working in pharmaceutical companies, hospitals, research labs, and attaining an MSc in Biomedical Science. He has a particular interest in how novel therapies can be applied to a range of common and rare neurological conditions.

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