What is MAC lung disease?

MAC lung disease is a lung infection caused by a group of bacteria called Mycobacterium avium complex (MAC).¹ These bacteria are commonly found in water, soil, and dust. The majority of people commonly inhale MAC bacteria regularly without falling ill, but some people, especially those with existing lung problems or weakened immune systems, can develop a lung infection, which is difficult to treat.² Unlike tuberculosis, MAC lung disease is not contagious.³

How MAC affects the lungs

MAC bacteria can infiltrate the lungs’ airways. Over time, they can cause inflammation and damage to lung tissue, which might lead to the formation of scars and holes.⁴ The infection makes it harder for the lungs to get rid of mucus and may result in respiratory problems. 

Common symptoms of MAC lung disease include:

• Chronic cough (can be dry or produce mucus)
• Fatigue (feeling very tired)
• Shortness of breath
• Chest discomfort or heaviness
• Low-grade fever
• Unintentional weight loss
• Loss of appetite
• Night Sweats
• Sometimes coughing up blood 

Symptoms can develop slowly and may be mistaken for other lung conditions. In some cases, fatigue may be the only noticeable symptom for a long time. 

Who is generally affected?

Anyone can get MAC lung disease, but it occurs most often in:

• Older adults
• People with chronic lung diseases like cystic fibrosis, bronchiectasis or chronic obstructive pulmonary disease (COPD)
• People with compromised immune systems, due to certain medications, cancer treatments or HIV/AIDS
• People who smoke or have a history of heavy smoking

Risk factors

The risk of getting MAC lung disease varies in each individual based on their health history or the condition of their lungs and immune system. People with weakened immune systems or existing lung problems such as COPD, bronchiectasis, or a history of severe pneumonia are more vulnerable because their bodies are less able to fight off the MAC bacteria. 

Understanding risk factors is crucial because MAC lung disease often develops slowly and its symptoms can be easy to miss or confuse with something else, which may lead to misdiagnosis or improper treatment.

Recognising symptoms sooner and seeking medical advice can improve clinical outcomes. If MAC lung disease is diagnosed early, treatment is likely to be successful and can avoid complications like antibiotic resistance or severe lung damage.

Chronic lung diseases as a risk factor

Chronic lung diseases are long-term conditions that damage the lungs and make it harder for them to function properly. These diseases weaken the lungs’ defences, making it easier for MAC bacteria to invade and cause infection. These includes illnesses like:

• COPD: Often caused by long-term smoking which damages the airways and air sacs in the lungs
• Bronchiectasis: Airways become enlarged and scarred, which leads to mucus build-up. The trapped mucus creates a perfect environment for bacteria like MAC to grow and cause infection
• Cystic fibrosis: Inherited disorder which causes thick, sticky mucus to build up in the lungs, increasing the risk of repeated infections, including MAC 
• History of severe lung infections: Individuals who have had serious lung infections in the past, such as pneumonia, might have lung damage that increases their susceptibility to MAC

When the lungs are healthy, they can clear out germs and bacteria. However, the lungs of people with long-term lung diseases could already be inflamed, scarred, or filled with thick mucus. MAC bacteria can hide and grow in the mucus accumulation and scarring caused by these disorders, and prolonged inflammation weakens lung tissue and facilitates the spread of infections. As a result of this damage, the lungs' capacity to effectively capture and eliminate foreign infections, such as the MAC bacterium, is diminished.

Immunosuppression as a risk factor

What is immunosuppression?

Immunosuppression means that a person’s own natural defence (immune system) against infections is weaker than usual. When the immune system is suppressed, it becomes more difficult for the body to fight off infections, including bacteria like MAC. Common causes of immunosuppression include:

• Medications: Certain medicines like steroids or chemotherapy can weaken the immune system^5,6
• Diseases: Illnesses such as HIV/AIDS, certain types of cancer, or autoimmune disorders may weaken the immune system
• Organ transplants: People who receive organ transplants are prescribed medications to stop their bodies from attacking the new organ (immunosuppressants), but these drugs also make it harder for them to fight off infections

Who should be more careful?

While anyone can be exposed to MAC bacteria, some people are more likely to develop MAC lung disease because their bodies are unable to fight off the infection. People at higher risk include:

• Age (people over 65): As people age, their immune systems naturally become less effective and lung function declines, making it easier for MAC to infect the body⁷
• Low body weight or being underweight: People who are underweight or have a low body mass index (BMI) are at increased risk due to the lack of muscle and fat to support the immune system⁸
• Smoking history: Smoking damages and weakens the lungs, making it easier for bacteria like MAC to cause infection. Recovering smokers may still have some increased risk due to lung damage⁹ 
• Other medical conditions: Vulnerability to MAC lung disease can be increased by certain health problems like:
  • Autoimmune diseases (e.g. rheumatoid arthritis) in which the immune system attacks the body’s own cells and tissues
  • Diabetes, which may impair immune function
  • History of cancer, especially if treatments (such as chemotherapy) have weakened the immune system

These risk factors can make it easier for MAC bacteria to infect the lungs, so individuals who have one or more of the factors should be attentive to their lung health and consult their healthcare provider if they notice any abnormalities.

Can MAC lung disease be prevented?

There is no guaranteed way to prevent MAC lung disease. However, for people at higher risk, there are simple steps that can help minimise the risk of getting infected:

• Don’t smoke or quit if you do: Smoking damages the lungs and increases the risk of infections like MAC lung disease. Quitting can help your lungs heal and reduce your risk over time. Avoiding exposure to secondhand smoke is also important for protecting your lung health
• Avoid dusty or damp environments: MAC bacteria thrive in places like construction sites, hot tubs or areas with stagnant water. Wear protective masks and limit exposure to these environments, especially if you have lung problems or a weak immune system 
• Manage chronic lung diseases with your healthcare provider: If you have a lung condition such as COPD, bronchiectasis, or asthma, regular check-ups and sticking to your treatment plan can help keep your lungs healthier and reduce the chance of infections.
• Use medications as prescribed: Some medications can weaken your immune system. Always follow your doctor’s instructions and discuss any concerns about infection risk 
• Maintain a healthy weight and lifestyle: Eating a balanced diet, exercising regularly, getting enough rest, and managing stress will boost your immune system and overall health 

What to do if you’re concerned?

It is crucial to pay attention to symptoms such as chronic cough, fatigue, unexplained weight loss or shortness of breath, especially if you have chronic lung disease or a weakened immune system. You should consider seeing a doctor if:

• You have a cough that lasts for several weeks
• You feel unusually tired or weak
• You experience unexpected weight loss
• You have trouble breathing or feel discomfort in your chest

Even if your symptoms are mild or have been mistaken for another lung problem, it’s important to get checked, as MAC lung disease can be serious and may worsen over time

What tests might be done

To diagnose MAC lung disease, several tests may be used, including:

• Chest X-rays or CT scans: To look for changes or damage in the lungs
• Sputum cultures: A sample is taken from your sputum and cultured to test for MAC bacteria
• Bronchoscopy: A procedure using a thin tube to look inside the lungs and collect samples if needed
• Blood tests: To rule out other possible causes 

These tests help doctors understand the bigger picture of your overall health and whether MAC bacteria might be present. 

An early diagnosis is crucial because MAC lung disease can cause damage to the lungs, leading to a decline in functionality if left untreated. A timely treatment can prevent the infection from worsening and reduce the risk of long-term complications. 

Summary

Mycobacterium avium complex (MAC) lung disease is a serious infection that primarily affects individuals with chronic lung conditions or weakened immune systems. Although MAC bacteria are commonly found in the environment, only susceptible individuals tend to develop illness. The disease progresses slowly and presents with symptoms such as chronic cough, fatigue, weight loss, and shortness of breath, which are often mistaken for other conditions.

Two major risk factors are chronic lung diseases (such as COPD, bronchiectasis, and cystic fibrosis) and immunosuppression due to medications, diseases like HIV/AIDS, or cancer treatments. People who are older, underweight, or have a history of smoking are also at higher risk.

While MAC lung disease cannot always be prevented, managing underlying conditions, avoiding environmental exposures, and maintaining a healthy lifestyle can help reduce risk. Early recognition of symptoms and prompt medical evaluation are crucial for effective treatment and avoiding long-term lung damage.