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.
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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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.
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.
MAC infections include:
There are two types of 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.
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:
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:
Your healthcare provider will perform a physical exam and ask about symptoms.
Tests for MAC lung disease include:
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:
These actions can ease MAC lung disease symptoms:
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.
These steps may lower your risk of exposure to MAC bacteria:
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.
You may want to ask your healthcare provider:
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.
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.
Last reviewed by a Cleveland Clinic medical professional on 12/01/2021.
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