Mycobacterium avium complex (MAC) lung infection: symptoms, diagnosis and treatment

Non-tuberculous mycobacteria, or NTM, are described by Asthma + Lung UK as a group of bacteria that can cause rare lung infections, sometimes called NTM pulmonary disease. They mainly affect people who have a lung condition or a weak immune system, such as asthma, bronchiectasis, cystic fibrosis, COPD or pulmonary fibrosis. Mycobacterium avium complex is the best-known member of the group in the UK.

The UK Health Security Agency (formerly Public Health England) study of NTM isolates in England, Wales and Northern Ireland between 2007 and 2012 found that the incidence of pulmonary MAC rose from 1.3 to 2.2 per 100,000, and that the majority of those individuals were over 60 years old. The authors also noted that pulmonary NTM disease may occur in people with no overt immune deficiency.

NTM are found in water and soil, according to Asthma + Lung UK, and everyone comes into contact with them in daily life. Only a small number of people go on to develop infection.

Asthma + Lung UK says symptoms may develop slowly and may include a cough and coughing up phlegm or blood, a high temperature of 38 degrees Celsius or above, losing weight and not feeling hungry, feeling very tired, feeling breathless more often and night sweats.

Because these resemble other lung infections and flare-ups of existing conditions, MAC can be hard to spot. Asthma + Lung UK advises that if you have long or repeated flare-ups of a condition such as bronchiectasis or COPD, you should ask your healthcare professional whether it could be an NTM infection. It also advises asking for testing if you live with a lung condition or weak immune system and have symptoms of an infection that will not go away or are getting worse despite your usual treatment.

Asthma + Lung UK says it can take time to diagnose an NTM infection. Your healthcare professional will ask about your medical history and arrange tests such as a phlegm (sputum) sample to look for NTM in your airways, an X-ray or CT scan to see the pattern of lung disease and any other lung problems, and spirometry to measure how much air you can breathe out. A FeNO test, and gas transfer and lung volume tests, may also be used. If you do not cough up any phlegm, you may need a bronchoscopy to get a sample.

Importantly, the charity notes that even if NTM are found in your phlegm, it does not mean you have an NTM lung infection. You may not always need treatment, as some people can clear the infection without needing antibiotics, and your doctor will explain your results and discuss whether treatment is needed.

Asthma + Lung UK says that if you are diagnosed with an NTM infection, your specialist team will monitor you closely. A specialist nurse is often assigned, and physiotherapists and dietitians may be involved. NTM infections can last for a year or two as the bacteria gets trapped by the phlegm in the lungs. Airway clearance and regular exercise can help to improve symptoms without needing antibiotics.

Antibiotics may be recommended if you continue to have symptoms or there is evidence of lung damage, such as inflammation or widened airways on a CT scan. The charity says you will be treated with a combination of several antibiotics, which often include rifampicin, ethambutol, azithromycin, clarithromycin, amikacin and isoniazid, usually as tablets or liquid, and that you may be treated for a year or two. If you take all your medication as prescribed, the infection should go.

Side effects vary by medicine. Asthma + Lung UK says rifampicin may turn urine, saliva, sweat or tears a red-orange colour, which is harmless, and that nausea, vomiting, diarrhoea and loss of appetite are common. It lists eyesight problems with ethambutol, rash, chills or high temperature, easy bruising, jaundice and numbness or tingling among rare effects to report immediately. Your team may arrange ECG or echocardiogram, blood tests, hearing tests and eye tests while you are on treatment.

Asthma + Lung UK says the best way to help your lungs fight off an NTM infection is to keep active and look after yourself: have vaccines you are able to, such as flu and pneumonia, eat a healthy balanced diet, take your medicines as prescribed, do chest clearance exercises regularly if you have bronchiectasis or cystic fibrosis, avoid people with respiratory infections and get help to stop smoking.

The charity says you cannot completely avoid NTM but suggests some ways to reduce exposure, including raising your water heater temperature above 55 degrees Celsius with a thermostatic mixing valve to avoid burns, taking short showers, cleaning the showerhead regularly, and only drinking boiled or filtered water. It also notes that there is no clear evidence that stopping gardening, not showering or giving up swimming reduces the risk of NTM infection.

NTM infections can come back, and the charity warns that forgetting or stopping medicines can allow the bacteria to become resistant to the antibiotics, making the infection much harder to treat. If you are having problems taking your medicines, speak to your specialist team.