How is MAC not contagious to another person with lung disease?

To answer your question, MAC/NTM needs to be inhaled in substantial quantity to cause an infection - such as in the vapor from a shower. The amount of NTM released by an infected person is not considered contagious.
Here is a pamphlet about the infection:
https://ntminfo.org/wp-content/uploads/2023/12/NTM-INSIGHT-Pamphlet_AA.pdf
I can tell you from personal experience that even though my partner and I both have Bronchiectasis, they never caught MAC from me in the 4-5 years I had it, before I was treated and during treatment. Believe me, I was concerned about it too, but both the pulmonologist and infectious disease doc assured us it would not spread, even though we shared a bed and bathroom. There are some other opportunistic infections, like Pseudomonas, that can possibly be spread by close contact.

@sueinmn did the MAC you had go away? How long did it take? Did you have any side effects to the medication?

@marycronin Yes, the MAC went away with antibiotics and airway clearance with 7% saline. That was in early 2020 and it has not returned. I still do airway clearance, with occasional use of 7% saline and my lungs remain clear of infection (but not mucus.) In addition to Bronchiectasis, I also have asthma and allergies, and one of the keys to avoiding infection is to keep those under control.

All in all, I live a pretty normal life after at least 8 years with Bronchiectasis.

@sueinmn did you experience any side effects from all the medication you had to take? I heard the side effects can be pretty serious.

Side effects are a common experience with long-term antibiotic therapy. I had several issues, including early nausea & diarrhea - resolved by taking a probiotic and timing the medication so I slept through the worst discomfort. I also had serious fatigue, but whether it was from the drugs or the infection is hard to say. I also had to switch one antibiotic early on due to intolerable nausea - long time ago, so I don't remember which one.

As for serious side effects, I avoided all alcohol and NSAIDs to protect my liver, since some of the meds are hard on it. I have had tinnitus for years - but whether the drugs made it worse, or aging or something else, I cannot say. My hearing was never great, but didn't get any worse with the meds; it is still monitored every year and seems to be in a slow downward slide, more related to age and heredity than the drugs. I had my eyes checked every 6 months based on my ophthalmologist's recommendation and had no eye issues.

All that said, the infection was severe - it would not have gone away by itself. I couldn't walk one block without coughing and having to rest. I had severe fatigue, a constant low-grade fever and was losing weight.

My diagnosis was MAC & Pseudomonas with Nodular Bronchiectasis & ground glass opacities, but no cavities. Knowing what I do now, if I had been less ill, I would have asked to try airway clearance with 7% saline for 6 months to see if I could knock the infection back.

@sueinmn thank you for comment back. That really helps!

@marycronin
I was diagnosed with bronchiectasis in 2021 followed by MAC. I had a bronchoscopy done in July and they sent the sample off to Jewish and I was diagnosed in September. I had developed a horrible cough after having Covid. I was a very healthy person and never smoked and didn’t have asthma. I was put on the big 3 for 9 months. I didn’t have too many side effects but I did have to have an EKG, eye exam and blood work done every month. I also had to go through pulmonary rehab. I no longer have MAC but now I have ABPA.

@sueinmn I am curious, knowing what you do now, would you take an antibiotic on a regular basis? my ID is putting me on an antibiotic 3x a week.

@ddoran9233 This is a highly individual decision, and needs to be done in conjunction with your care team, considering all of your medical issues, and the type of NTM you have (while most grow slowly, some like M Abscessus can progress rapidly.) Also, if you have other infections like Pseudomonas, it is preferable to treat them first as they usually are easier to knock down.

In my case, I would take the antibiotics (Big3) again - I had Pseudomonas that had weakened me and took 4 courses of antibiotics to clear, during that time my MAC got worse. My condition was severe, I was coughing non-stop, losing weight, running a fever, had crushing fatigue and could not even walk a block.

IF on the other hand, I was not symptomatic or had few symptoms, and did not have any cavities or large nodules, and knowing what we have all learned these past 8+ years, I would ask to do "active watching and waiting." That would be twice daily airway clearance with 7% saline nebs, regular sputum cultures, and at least twice yearly CT scans. If after 6 months or a year of the conservative treatment, I was getting worse, I would try the antibiotics.

Age and overall physical condition also play a part - if I was in generally poor health and thought I could not tolerate the 3 antibiotic regimen, I would ask to do what we did for my Mom when she was in that situation. We just treated exacerbations as they occurred. When she finally died after several years of declining health, MAC was not her cause of death - it was one of her several other serious health problems.

Are you in the situation of considering antibiotic therapy? Are you working with a care team you trust?

@sueinmn Thank you for your reply and sharing your experience. What you went through sounds difficult and exhausting and I wish you did not have to go through that.
I am considering antibiotics 3x per week prescribed by the ID dr and will review with the new pulmonologist but it is concerning and no, at this time, I do not fully trust my care team. Specifically because I do not have all the disciplines. Allergies and asthma are at the root of my condition and thankfully, my allergist is phenomenal. I do need a way to reduce the inflammation and prevent re-occurring infections and airway clearance may not be enough. I do like the thought of the monitoring approach but I need to discuss this with the new pulmonologist as I cannot assess the risk on my own. My diagnosis is very new (Nov 2025) so it will take some time to find the right team and develop a care plan. This site, all the feedback, has been tremendously helpful especially learning about airway clearance techniques and I have already seen an improvement. I appreciate you insights and experience.