What are the Risk Factors for MAC Lung Disease?

Existing health conditions and other factors can put a person at a greater risk for this serious bacterial infection.

MAC lung disease is more prevalent among people who are over the age of 65 and women who have gone through menopause.

Medically reviewed in November 2022

MAC lung disease is a bacterial infection of the lungs caused by Mycobacterium Avium Complex (MAC), multiple strains of bacteria that are commonly found in soil and water. These bacteria are a type of nontuberculosis mycobacteria (NTM).

For most people, exposure to these bacteria is harmless. For others—including people who are older, have a weakened immune system, or a pre-existing condition that affects the airways—exposure to these bacteria can cause a serious respiratory infection. MAC lung disease can be cured, but it can take a long time. Treatment involves taking multiple antibiotics for 12 months or longer.

How does a person get MAC lung disease?
NTM bacteria can enter the body through the airways when a person breathes in dust or soil in the air. NTM bacteria can also enter the body from contaminated drinking water. Once inside the body, these bacteria grow slowly, causing a low-grade infection and inflammation. Over time—often many years—the infection can become more severe.

As mentioned above, many people are exposed to these bacteria, but few people develop infections. It’s also important to mention that MAC lung disease is not contagious—it cannot spread from one person to another.

Who is at risk for MAC?
It is not fully understood why some people develop an infection when exposed to the bacteria that cause MAC lung disease, or why most people do not develop any illness after exposure.

It is known that people who have certain existing health conditions are more likely to have MAC lung disease. These include conditions that affect how air moves in and out of the lungs, as well as conditions or circumstances that cause a person to have a weakened immune system. Conditions that are known to make a person more susceptible to an infection from NTM bacteria include:

  • Chronic obstructive pulmonary disease (COPD), a condition where the tissues of the lungs are damaged, making it difficult for a person to breathe. There are two main types of COPD, chronic bronchitis and emphysema. In most cases, COPD is the result of cigarette smoking.
  • Bronchiectasis. This is a condition that occurs when there is damage to the large airways that connect the lungs to the windpipe (the bronchi). As a result, the airways become scarred, thickened, and abnormally wide and unable to clear out mucus. This leads to recurring infections, difficulty breathing, and loss of lung function. Risk factors include recurring infections (such as pneumonia, whooping cough, and fungal infections) as well as inflammatory conditions, autoimmune diseases, and immunodeficiency disorders. However, many cases are idiopathic, meaning no cause can be identified.
  • Cystic fibrosis. This is a genetic disorder that causes the body to produce abnormally thick and sticky mucus, which clogs the airways and other passageways throughout the body. People who have cystic fibrosis have the condition at birth. The thickened mucus produced when a person has cystic fibrosis makes it difficult for the airways to clear out germs, which can become trapped and lead to infection.
  • Other damage to the lungs. For example, damage caused by cigarette smoking or from a previous tuberculosis (TB) infection.
  • Weakened immune system. People who have untreated HIV or who take medications that compromise the immune system are also at an increased risk.

Age and menopause are other risk factors worth mentioning. MAC lung disease is more prevalent among people who are over the age of 65 and women who have gone through menopause.

Article sources open article sources

Cleveland Clinic. MAC Lung Disease.
American Lung Association. MAC Lung Disease.
Merck Manuals. Infections Caused by Bacteria Related to Tuberculosis (TB).
Sheng-Wei Pan, Chin-Chung Shu, Jia-Yih Feng, and Wei-Juin Su. Treatment for Mycobacterium avium complex lung disease. Journal of the Formosan Medical Association, 2020. Vol. 119. Suppl. 1.
National Organization for Rare Disorders. Nontuberculous Mycobacterial Lung Disease.
NCI Dictionary. COPD.
American Lung Association. COPD Causes and Risk Factors.
American Lung Association. Learn About Bronchiectasis.
National Heart, Lung, and Blood Institute. Bronchiectasis.
National Heart, Lung, and Blood Institute. What Is Cystic Fibrosis?
Centers for Disease Control and Prevention. Cystic Fibrosis.

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