Table of ContentsView AllTable of ContentsTransmissionRisk FactorsSymptomsDiagnosisTreatmentCauses of Severe InfectionPrognosis and Curability
Table of ContentsView All
View All
Table of Contents
Transmission
Risk Factors
Symptoms
Diagnosis
Treatment
Causes of Severe Infection
Prognosis and Curability
Mycobacterium avium complex (MAC) is group of organisms causing abacterial infectionthat leads to lung disease. MAC is noncontagious and made up of nontuberculous mycobacteria (NTM), which are highly prevalent organisms in the United States typically found in drinking water, soil, or aerosols.
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Spread of Mycobacterium Avium Complex (MAC) Infection
A MAC infection is not contagious, so it doesn’t spread through human contact or respiratory droplets like other types of bacterial infections.
Instead, it is contracted through inhaling or ingesting contaminated substances containing the bacteria, typically drinking water, soil, or aerosols, such as those that come off shower heads or hot tubs.
MAC SubtypesThere are three subtypes of MAC:M. aviumsubspecieshominissuis, the human typeM. aviumsubspeciesaviumserotype 1, 2 and 3, andM. aviumsubspeciessilvaticum, the bird typeM. aviumsubspeciesparatuberculosis, the ruminant type found in the stomach of animals that eat plants
MAC Subtypes
There are three subtypes of MAC:M. aviumsubspecieshominissuis, the human typeM. aviumsubspeciesaviumserotype 1, 2 and 3, andM. aviumsubspeciessilvaticum, the bird typeM. aviumsubspeciesparatuberculosis, the ruminant type found in the stomach of animals that eat plants
There are three subtypes of MAC:
Risk Factors and Vulnerable Demographics
People with no underlying health conditions that affect the lungs or immune system often inhale or ingest MAC, and it does not cause any issues. However, vulnerable demographics can develop severe lung infections when they come into contact with the bacteria.
People most vulnerable to MAC include:
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Characteristic Symptoms
When people ingest or inhale MAC, the bacterial infection begins to cause inflammation, lung damage, and scarring. Over time, that damage worsens, making it a progressive infection.
After a while of living with the illness and the ensuing damage, the airways become compromised and cannot perform as they should or clear mucus properly. This leads to recurrent infections, such aspneumoniaorbronchitis.
When symptoms develop, they can include:
Asymptomatic MAC and Delayed DiagnosisIn some cases, MAC infections can be asymptomatic. One study looked at people with the infection and found that 15.7% presented without symptoms but still had signs of lung damage.Not showing symptoms of MAC can lead to a delayed diagnosis, interfere with successful treatment, and cause the progression of lung damage.
Asymptomatic MAC and Delayed Diagnosis
In some cases, MAC infections can be asymptomatic. One study looked at people with the infection and found that 15.7% presented without symptoms but still had signs of lung damage.Not showing symptoms of MAC can lead to a delayed diagnosis, interfere with successful treatment, and cause the progression of lung damage.
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MAC Diagnosis vs. Differential Diagnoses
The signs and symptoms of MAC are similar to those of other lung diseases, which can make diagnosing the infection challenging.
In some cases, diagnosis can be delayed for months or years after contracting the infection, which can worsen patient outcomes.
Testing, exams, and checkups
A series of steps is involved in correctly diagnosing MAC in those with the infection. They include:
Repeated Sputum Tests to Reduce False PositivesSince MAC can be present in the airways but not cause lung damage, the sputum lab culture may be performed several times and on different days to get a definitive positive or negative result.
Repeated Sputum Tests to Reduce False Positives
Since MAC can be present in the airways but not cause lung damage, the sputum lab culture may be performed several times and on different days to get a definitive positive or negative result.
Long-Term MAC Treatment
Treatment for MAC isn’t always done at the first sign of infection. Instead, healthcare providers will try to determine the progression of the disease before offering treatment options.
They do this to avoid giving unnecessaryantibiotictreatments to those who will clear the infection on their own.
The factors that go into determining if treatment is needed right away include:
If these factors are not met, your healthcare provider may monitor symptoms until the disease begins to progress, at which time they will start treatment.
Antibiotic Types and Effectiveness
When treatment for MAC is done, healthcare providers use a combination of antibiotics to knock out the bacteria.
The treatment recommendations include using threedifferent types, including rifampin, ethambutol, and clarithromycin orazithromycin, administered to the person for 12 months following negative sputum cultures.
Other drugs may also be added to the treatment plan, including Vetstrep (streptomycin) and Amikin (amikacin).These are reserved for people who have severe disease with extensive lung damage. Typically, the doses are given three times per week or daily.
How Effective Is Treatment?Success rates for treatment vary depending on the individual and disease severity. According to research, success rates can range from 32% to 65%, with the three-drug regimen being the most effective form of treatment. If antibiotic treatment is not effective, surgery may be beneficial for those with the infection. Surgery can be used to remove damaged areas of the lung or to stop persistent bleeding.
How Effective Is Treatment?
Success rates for treatment vary depending on the individual and disease severity. According to research, success rates can range from 32% to 65%, with the three-drug regimen being the most effective form of treatment. If antibiotic treatment is not effective, surgery may be beneficial for those with the infection. Surgery can be used to remove damaged areas of the lung or to stop persistent bleeding.
What Happens If You Miss an Antibiotic Dose
Reasons for Severe, Prolonged, or Recurrent Infection
Antibiotic Resistance and MACIn some cases,antibiotic resistancemay develop in those with MAC infections. This means that the antibiotics no longer work for the same strain of the bacteria. It usually happens with one specific drug, macrolide monotherapy, and changes the course of treatment. Other antibiotics will then have to be used to treat MAC infections.
Antibiotic Resistance and MAC
In some cases,antibiotic resistancemay develop in those with MAC infections. This means that the antibiotics no longer work for the same strain of the bacteria. It usually happens with one specific drug, macrolide monotherapy, and changes the course of treatment. Other antibiotics will then have to be used to treat MAC infections.
MAC-attributable mortality is difficult to discern and it varies in different studies from 5% to 40%. This wide range is owing to differences in coexisting medical conditions and age, with older people and those who have comorbidities (co-occurring medical conditions) or a more severe illnesses having a greater risk for death if they incidentally also have MAC.
Summary
MAC is a bacterial infection that causes lung damage and scarring. The several bacteria that make up MAC are highly prevalent and can be inhaled every day. However, in healthy people, it doesn’t cause any issues. In those with underlying health conditions that affect the lungs or immune system, the infection can become severe and require treatment.
Treatment involves antibiotics, as they are the only drugs used to counter bacterial infections. Since MAC can be severe, there is a 25% mortality rate associated with the disease. Knowing the signs of infection and understanding your personal risk factors can help you seek the appropriate care if you believe you have a MAC infection.
10 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.American Lung Association.Learn about nontuberculous (NTM) lung disease.Tran QT, Han XY.Subspecies identification and significance of 257 clinical strains of Mycobacterium avium.J Clin Microbiol.2014 Apr;52(4):1201-6. doi:10.1128/JCM.03399-13American Lung Association.MAC lung disease.University of Texas Health Sciences Center.Frequently asked questions about mycobacterial avium intracellulare complex (MAC) from a patient’s perspective.Fujiwara K, Watanabe F, Uesugi F, Furuuchi K, Ito M, Kodama T, Tanaka Y, Yoshiyama T, Mitarai S, Kurashima A, Ohta K, Morimoto K.Beyond symptoms: Radiologic identification of asymptomatic Mycobacterium avium complex pulmonary infections.Respir Med.2024 May;226:107627. doi:10.1016/j.rmed.2024.107627American Lung Association.Symptoms and diagnosis of NTM lung disease.Kwon YS, Koh WJ, Daley CL.Treatment ofMycobacterium aviumcomplex pulmonary disease.Tuberc Respir Dis (Seoul).2019 Jan;82(1):15-26. doi:10.4046/trd.2018.0060American Lung Association.Treating and managing NTM lung disease.Boyle DP, Zembower TR, Qi C.Relapse versus reinfection ofmycobacterium aviumcomplex pulmonary disease. Patient characteristics and macrolide susceptibility. doi:10.1513/AnnalsATS.201605-344BC.Diel R, Lipman M, Hoefsloot W.High mortality in patients with Mycobacterium avium complex lung disease: A systematic review.BMC Infect Dis.2018 May 3;18(1):206. doi:10.1186/s12879-018-3113-x
10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.American Lung Association.Learn about nontuberculous (NTM) lung disease.Tran QT, Han XY.Subspecies identification and significance of 257 clinical strains of Mycobacterium avium.J Clin Microbiol.2014 Apr;52(4):1201-6. doi:10.1128/JCM.03399-13American Lung Association.MAC lung disease.University of Texas Health Sciences Center.Frequently asked questions about mycobacterial avium intracellulare complex (MAC) from a patient’s perspective.Fujiwara K, Watanabe F, Uesugi F, Furuuchi K, Ito M, Kodama T, Tanaka Y, Yoshiyama T, Mitarai S, Kurashima A, Ohta K, Morimoto K.Beyond symptoms: Radiologic identification of asymptomatic Mycobacterium avium complex pulmonary infections.Respir Med.2024 May;226:107627. doi:10.1016/j.rmed.2024.107627American Lung Association.Symptoms and diagnosis of NTM lung disease.Kwon YS, Koh WJ, Daley CL.Treatment ofMycobacterium aviumcomplex pulmonary disease.Tuberc Respir Dis (Seoul).2019 Jan;82(1):15-26. doi:10.4046/trd.2018.0060American Lung Association.Treating and managing NTM lung disease.Boyle DP, Zembower TR, Qi C.Relapse versus reinfection ofmycobacterium aviumcomplex pulmonary disease. Patient characteristics and macrolide susceptibility. doi:10.1513/AnnalsATS.201605-344BC.Diel R, Lipman M, Hoefsloot W.High mortality in patients with Mycobacterium avium complex lung disease: A systematic review.BMC Infect Dis.2018 May 3;18(1):206. doi:10.1186/s12879-018-3113-x
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
American Lung Association.Learn about nontuberculous (NTM) lung disease.Tran QT, Han XY.Subspecies identification and significance of 257 clinical strains of Mycobacterium avium.J Clin Microbiol.2014 Apr;52(4):1201-6. doi:10.1128/JCM.03399-13American Lung Association.MAC lung disease.University of Texas Health Sciences Center.Frequently asked questions about mycobacterial avium intracellulare complex (MAC) from a patient’s perspective.Fujiwara K, Watanabe F, Uesugi F, Furuuchi K, Ito M, Kodama T, Tanaka Y, Yoshiyama T, Mitarai S, Kurashima A, Ohta K, Morimoto K.Beyond symptoms: Radiologic identification of asymptomatic Mycobacterium avium complex pulmonary infections.Respir Med.2024 May;226:107627. doi:10.1016/j.rmed.2024.107627American Lung Association.Symptoms and diagnosis of NTM lung disease.Kwon YS, Koh WJ, Daley CL.Treatment ofMycobacterium aviumcomplex pulmonary disease.Tuberc Respir Dis (Seoul).2019 Jan;82(1):15-26. doi:10.4046/trd.2018.0060American Lung Association.Treating and managing NTM lung disease.Boyle DP, Zembower TR, Qi C.Relapse versus reinfection ofmycobacterium aviumcomplex pulmonary disease. Patient characteristics and macrolide susceptibility. doi:10.1513/AnnalsATS.201605-344BC.Diel R, Lipman M, Hoefsloot W.High mortality in patients with Mycobacterium avium complex lung disease: A systematic review.BMC Infect Dis.2018 May 3;18(1):206. doi:10.1186/s12879-018-3113-x
American Lung Association.Learn about nontuberculous (NTM) lung disease.
Tran QT, Han XY.Subspecies identification and significance of 257 clinical strains of Mycobacterium avium.J Clin Microbiol.2014 Apr;52(4):1201-6. doi:10.1128/JCM.03399-13
American Lung Association.MAC lung disease.
University of Texas Health Sciences Center.Frequently asked questions about mycobacterial avium intracellulare complex (MAC) from a patient’s perspective.
Fujiwara K, Watanabe F, Uesugi F, Furuuchi K, Ito M, Kodama T, Tanaka Y, Yoshiyama T, Mitarai S, Kurashima A, Ohta K, Morimoto K.Beyond symptoms: Radiologic identification of asymptomatic Mycobacterium avium complex pulmonary infections.Respir Med.2024 May;226:107627. doi:10.1016/j.rmed.2024.107627
American Lung Association.Symptoms and diagnosis of NTM lung disease.
Kwon YS, Koh WJ, Daley CL.Treatment ofMycobacterium aviumcomplex pulmonary disease.Tuberc Respir Dis (Seoul).2019 Jan;82(1):15-26. doi:10.4046/trd.2018.0060
American Lung Association.Treating and managing NTM lung disease.
Boyle DP, Zembower TR, Qi C.Relapse versus reinfection ofmycobacterium aviumcomplex pulmonary disease. Patient characteristics and macrolide susceptibility. doi:10.1513/AnnalsATS.201605-344BC.
Diel R, Lipman M, Hoefsloot W.High mortality in patients with Mycobacterium avium complex lung disease: A systematic review.BMC Infect Dis.2018 May 3;18(1):206. doi:10.1186/s12879-018-3113-x
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