Germs, like plants and animals, are grouped into “families.” One such family is called Mycobacteria. This family of germs is divided into smaller groups called species, many of which can cause human disease. The most commonly recognized species is Mycobacterium tuberculosis, which causes a contagious lung disease in humans called tuberculosis. This disease is spread by person-to-person contact by coughing. To get more patient information about MAC, please visit www.maclungdisease.org.
What is MAC?
You have been diagnosed with a lung disease caused by a related germ called Mycobacterium avium complex. We refer to that germ as MAC. The difference between your germ and the germ that causes tuberculosis is that your germ is not spread by person-to-person contact and is not considered to be contagious. MAC infection is acquired from the environment. We do not know how or why people become infected with this MAC germ.
Although we can easily recover the germ from soil, water, and air samples, most people do not become sick from this organism (fewer than one in 10,000). Scientists and physicians who study these germs, think that perhaps the people who become infected have some defect in the structure or function of their lungs or in their immune systems. There are three recognized risk factors that make you more likely to develop this disease:
- Previous tuberculosis
- Heavy smoking
- Breathing tube disease called bronchiectasis
Disease in men most commonly relates to heavy smoking, while disease in women most commonly relates to bronchiectasis. Together with other related mycobacteria, which also are not contagious, MAC is a member of a group of germs called nontuberculous mycobacteria (or NTM).
The most common NTM germs involved in human infection are Mycobacterium avium complex (MAC), M. kansasii, M. chelonae, and M. abscessus. These germs can also cause disease in the skin (usually following local injury), but the most common organ affected is the lung. Diagnosis of these infections usually depends on growing the germ from coughed up lung samples (sputum). For a diagnosis of MAC lung infection to be made, the following tests or evaluations are usually performed:
- Medical history: a recording of your symptoms, such as cough, weight loss, sputum production, fatigue, fever, night sweats, etc.
- Chest x-ray: makes a picture of your lungs internally to diagnosis disease or infections
- CAT scan: a type of x-ray that shows the lung in greater detail than a plain chest x-ray
- Sputum culture: several are usually performed; specimen coughed up from your lungs is examined under a microscope and put on special media to grow the germs
- More complicated laboratory diagnostic procedures: sometimes these may be necessary to properly diagnose NTM, such as putting a tube down into your lungs (this procedure is called a bronchoscopy)
Our hospital and research laboratory at UT Health Science Center has been working for more than 15 years with the Food and Drug Administration (FDA) and several pharmaceutical companies (who make drugs called antibiotics which fight against these germs) to find ways to better treat these NTM infections, especially MAC. Most NTM are resistant to the ordinary antibiotics used to treat them and, in the past, many treatments have failed. A combination of several newly available drugs along with some TB drugs has recently been used successfully to treat these NTM infections, including MAC.
Your local physician or health department may have referred you to UT Health because of our expertise in treating MAC and the good results of our treatment protocols. The combination and doses of drugs given to you will be based upon your clinical history, age, weight, and symptoms, as well as the results of your chest x-ray and sputum cultures. Using this information and our experience, we can determine the amount of each drug, how often you need to take it, and the length of time you need to take it so that you receive the greatest benefit and are spared as many side effects as possible.
“Treatment trials” involve the use of these FDA-approved drugs, but all patients in the trial receive the same doses of the same drugs at the same frequency. More than 300 patients have participated in these trials during the past 15 years.
Current standard treatment of MAC lung infection involves three drugs (biaxin, ethambutol, and rifampin) taken three times a week for a minimum of 15-18 months. Because many of these drugs have side effects, you should be monitored carefully while you are taking them. Monthly labs tests to check liver function, eye checks, and sputum cultures are necessary while you are on these drugs. Because NTM usually grow slowly in the body, it may take years for your disease to be recognized. However, treatment is essential in controlling and curing the diseases caused by NTM.
- Formerly known as “atypical mycobacteria,” “atypical TB,” or “atypical AFB” and currently as “nontuberculous mycobacteria” or “NTM”
- Related to Mycobacterium tuberculosis (Mtb) but it is not TB.
- NTM includes a number of different species, but the most common one causing disease is MAC.
- MAC is not spread person to person like Mtb. MAC is not contagious.
- MAC lung disease seen in HIV (-) (non-AIDS) patients is a chronic lung infection and is often misdiagnosed as chronic bronchitis or recurrent pneumonia.
- MAC infection is often acquired from the environment (soil, air, natural waters, tap water, etc.)
- Scientists and physicians who have studied MAC believe people become infected because of a defect in the structure or function of their lungs (especially a disease called bronchiectasis) or in their immune systems.
- Damaged lung tissue can result from previous TB, heavy smoking, and a breathing-tube disease called bronchiectasis.
- Bronchiectasis is a breathing-tube (bronchial) disorder characterized by excessive mucus production, cough, and susceptibility to MAC or infections caused by the bacteria Pseudomonas aeruginosa.
- Disease in men commonly relates to smoking while disease in women (non-smoking) usually relates to bronchiectasis.
- The average age of patients with MAC lung disease in men is 55 years and 67 years in women.
- Men are more likely to have cavitary MAC (holes in their lungs).
- Women are more likely to have non-cavitary, nodular MAC.
- Diagnosis of MAC usually requires:
- Medical history with records of symptoms like cough, fever, weight loss, fatigue, sputum production, night sweats
- Chest x-ray (a picture of your lungs internally)
- High resolution CAT scan (similar to an x-ray but a more detailed picture)
- Sputum culture – several sputum cultures are usually performed. Your specimen coughed from your lungs is examined under a microscope (AFB smear) and also placed on special media to grow mycobacteria (AFB culture).
- Bronchoscopy – may be necessary in some cases (especially if you can’t cough up sputum) but not all, and involves putting a tube down into your lungs to obtain specimens for culture.
- Treatment of MAC requires a multi-drug regimen (more than one drug).
- MAC is resistant to ordinary antibiotics.
- Combination of three FDA-approved drugs/dosages are based upon your clinical history, age, weight, and symptoms.
- Clarithromycin (Biaxin) or Azithromycin (Zithromax)
- Rifampin (Rifadin) or Rifabutin (Mycobutin)
- Ethambutol (Myambutol)
- The combination of medicines is given until no more MAC germs can be grown in culture from your sputum for one year. Average treatment period is about 15-18 months.
- Monthly sputum cultures are performed while you are on therapy, and periodically when you finish your therapy to be sure your MAC is gone.
- The three-drug regimen is given three times weekly (preferably Monday-Wednesday-Friday)
- Data from previous treatment trials tell us that most patients (about 80 percent) who can tolerate the appropriate medicines will get better and may be cured.
- Patients who take the three-drug regimen for less than one year with negative cultures are more likely to develop another infection or have a relapse.
- Patients whose MAC doesn’t’ clear up after the three-drug therapy are usually required to take additional injectable medicines, which may help.
- Monthly laboratory tests to check kidneys and liver along with a complete blood count (CBC) are necessary while you are taking the medicines.
- Most common potential side effects/complications of medicines:
- Clarithromycin: Loss of appetite, diarrhea, nausea, abdominal pain, abnormal liver function tests, bitter taste, mild allergic rash.
- Azithromycin: Diarrhea, nausea, abdominal pain, abnormal liver function tests, decreased hearing, tinnitus (sounds in ears).
- Rifampin: Nausea, vomiting, liver damage, decreased platelets (cells which clot blood), body secretions are orange/red.
- Rifabutin: Nausea, vomiting, decreased platelets, decreased white blood cells (cells which fight infection), eye pain, diffuse muscle and joint aches, skin pigmentation (orange).
- Ethambutol: Decrease in vision (especially color vision), blurriness.
- Streptomycin: Kidney damage, tinnitus, hearing loss, poor balance, numbness, tingling, muscle damage, fever, headache.
- Amikacin: Kidney damage, hearing loss, poor balance, muscle damage, fever, headache, numbness.
- Barbara Brown-Elliott, MS, MT(ASCP)SM
- Megan Devine, MD
- James Fox, MD
- Pamela McShane, MD
- Julie Philley, MD
- Richard J. Wallace Jr., MD