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Mycobacterium avium complex (MAC), a type of nontuberculous mycobacteria (NTM), lives all around us. You’ll find these germs in dirt, dust, and drinking water. They’re also common in natural sources like lakes or rivers. MAC can cling to wet surfaces like your shower or the plumbing inside your home or office building, too.

They’re usually harmless, but they can make some people sick. Here’s what to watch out for.

Does Lung Disease Raise Your Risk of MAC Infection?

Most people don’t have health issues when they breathe these microbes in. But MAC bacteria are the most common cause of nontuberculous mycobacteria lung disease. And your odds of this kind of infection go up with any condition that damages your lungs.

Most people who get a MAC infection have at least one underlying lung disease. That includes:

  • Bronchiectasis
  • Chronic obstructive pulmonary disease (COPD)
  • Cystic fibrosis
  • Silicosis, a type of pulmonary fibrosis


  • Chronic bronchitis
  • Previous tuberculosis infection
  • Lung cancer
  • Emphysema
  • Rheumatoid arthritis that affects your lungs

Other factors that may hurt your lungs and airways include:

  • Air pollution
  • Asthma
  • Gastroesophageal reflux disease (GERD)
  • Smoking for many years

MAC lung disease can be serious, but it tends to grow slowly. See your doctor if you have:

  • New symptoms of fatigue or weight loss, along with:
  • A cough that doesn’t go away
  • Shortness of breath, night sweats, or coughing up blood

Do Older Women Get MAC Infections More Often?

Anyone can get MAC. But according to decades of research, these infections seem to show up more often in women with a low body mass index (BMI) who’ve gone through menopause.

These folks are also more likely to have:

  • Scoliosis (when your spine curves)
  • Pectus excavatum (when your breastbone sinks into your chest)
  • Mitral valve prolapse (a heart valve condition)

But there’s evidence MAC lung infections are on the rise among middle-aged to older women regardless of BMI. Experts aren’t sure why. They think it may be a mix of sex hormones, immune cells, and environmental factors. 

Does a Weak Immune System Raise Your Risk of MAC Infection?

MAC is considered an opportunistic infection. That means these germs usually don’t cause disease. But they can make you sick if you’re exposed to them when your immune system isn’t very strong. 

Certain conditions or drug treatments can weaken your immune system. That includes:

HIV/AIDS. MAC is commonly seen in people with a very low CD4 count. If you have HIV, talk to your doctor about antiretroviral therapy (ART). ART is the best way to avoid future infections.

Blood cancer. These are diseases like leukemia and lymphoma.  

Immune-suppressing medication. Your doctor may give you drugs to slow down your immune system on purpose. This can be a good thing. You may need these meds to stay healthy if you get an organ transplant or have an autoimmune condition like rheumatoid arthritis.

But these medications can also raise your odds of infections. That might include drugs such as:  

  • Oral or inhaled steroids
  • Biologics, especially anti-TNF drugs
  • Other immunosuppressive agents

Primary immune deficiency disease (PIDD). Rarely, you can have a genetic condition that makes your immune system less effective. You might grow up with a PIDD and not get diagnosed until you’re an adult.

Some examples of PIDDs that boost your chances of a MAC infection include:

  • Severe combined immunodeficiency (SCID)
  • Mendelian susceptibility to mycobacterial disease (MSMD)
  • Autoantibody disorders

What Are Nontuberculous Mycobacteria Autoantibodies?

Antibodies are proteins your immune cells make to fight germs. Autoantibodies are antibodies your body makes against itself. This can happen if your immune system can’t tell the difference between your own cells and bacteria, viruses, or other foreign invaders.

Some folks who get NTM infections test positive for autoantibodies called anti-interferon gamma (IFN-gamma). Scientists think IFN-gamma plays a key part in how the body controls NTM and other opportunistic infections. There’s ongoing research in this area.

It’s not common to check for IFN-gamma autoantibodies. The tests can be expensive. And right now, there’s no way to fix this kind of immune issue. But it’s something you can ask your doctor about if you get an MAC infection.

Can Healthy Children Get MAC Infections?

It’s uncommon for kids with a normal immune system to get this kind of bacterial infection. But it can happen, usually in children between the ages of 1 and 5. Scientists think this is because young kids like to play in the dirt or put things in their mouths.

Most kids exposed to MAC don’t have health problems. But some might get a MAC-associated lymph node infection. If it happens to your child, they’re most likely to have swollen lymph nodes in their neck. This is called cervical lymphadenitis.

Less often, children can get other kinds of MAC infections. That includes disease that affects their skin, lungs, or whole body. Your child may need antibiotics or surgery to get better. You doctor will let you know which treatment is best.

Do Lifestyle Factors Play a Role in MAC Infection?

Keep in mind it’s not your fault if you get sick. And it’s impossible to avoid these germs completely. They’re really hard to kill, even with disinfectant or hot water heaters.

But if you’re more likely to get an infection, you might want to take extra steps to lessen your exposure to MAC.

You’ll want to:

  • Skip hot tubs or saunas.
  • Use the vent fan in your bathroom and kitchen.
  • Set your water heater to at least 130 degrees F.
  • Wear a mask when you’re digging in the dirt.
  • Wet potting soil before you use it.
  • Stay away from misty showers or sinks.

Talk to your doctor about more ways to avoid a MAC infection. If you do get sick, they’ll help you find the best treatment to get better.

Show Sources

Photo Credit: Wand_Prapan / Getty Images


CDC: “Healthcare-Associated Infections (HAIs) – Nontuberculous Mycobacteria (NTM).”

American Lung Association: “Learn about NTM Lung Disease,” “MAC Lung Disease.”

Annals of the American Thoracic Society: “Incidence and Prevalence of Nontuberculous Mycobacterial Lung Disease in a Large U.S. Managed Care Health Plan, 2008-2015.”

Frontiers in Immunology: “The Rise of Non-Tuberculosis Mycobacterial Lung Disease,” “The New Frontier of Host-Directed Therapies for Mycobacterium avium Complex

Indian Journal of Medical Research: “Epidemiology, diagnosis & treatment of non-tuberculous mycobacterial diseases.”

Merck Manual: “Infections Caused by Bacteria Related to Tuberculosis (TB).”

Pathogens: “Non-Tuberculous Mycobacterial Diseases in Children.”

Gender Medicine: “Slender, older women appear to be more susceptible to nontuberculous mycobacterial lung disease.”

Cleveland Clinic: “Nontuberculous Mycobacteria Infections,” “MAC Lung Disease.”

National Organization for Rare Disorders (NORD): “NIH GARD Information: Mycobacterium Avium Complex infections.” “Disseminated Mycobacterium avium Complex Disease.”

Respirology: “Middle-aged to elderly women have a higher asymptomatic infection rate with Mycobacterium avium complex, regardless of body habitus.”

BMC Infectious Diseases: “High mortality in patients with Mycobacterium avium complex lung disease: a systematic review,” “Disseminated Mycobacterium avium complex infection mimicking malignancy in a patient with anti-IFN-y autoantibodies: a case report.”

The Journal of Infectious Diseases: “Mycobacterium avium Complex: Addressing Gaps in Diagnosis and Management.”

National Institute of Allergy and Infectious Diseases: “Primary Immune Deficiency Diseases (PIDDs).”

Experimental Biology and Medicine: “Minireview: Insights into anti-interferon-y autoantibodies.”

PeerJ: “Epidemiology of and risk factors for extrapulmonary nontuberculous mycobacterial infections in Northeast Thailand.”

Clinical Infectious Diseases: “When to Test for Anti-Interferon-y Autoantibody?”

American Academy of Pediatrics: “Nontuberculous Mycobacterial Infections in Children.”