Let’s Think About MAC
And to clarify, the lung infection
Conducting an internet search for “MAC” yields results predominantly on computers. Perhaps this is the first thing that crosses your mind when MAC is mentioned. Hopefully, in the not too distant future, that will change for good. So, what should you think when you hear MAC? Simple. Lung infection. Why? Would the thought of multi-drug resistant TB (MDR-TB) scare you? Well, according to the American Thoracic Society (ATS), the drug management of macrolide-resistant NTM MAC is analogous to that of MDR-TB.1
The link between NTM and MAC.
Capable of causing serious pulmonary infections, Non Tuberculous Mycobacteria (NTM) are naturally occurring organisms found throughout the environment.2 3 A pulmonary infection caused by NTM can lead to a progressive decline in lung function, radiographic disease progression, a worsening of symptoms and a significant decline in health-related quality of life.4 5 6 7 8 9
Mycobacterium avium complex (MAC) are one of most common species of NTM causing pulmonary disease,10 and between 2007 and 2012, 35.6% of all culture positive pulmonary NTM isolates in the UK were found to be MAC.11 Chronic, isolating and potentially debilitating, NTM MAC pulmonary disease can severely impact a patient’s health-related quality of life and puts unnecessary pressure on the entire healthcare system. Furthermore, MAC pulmonary disease is associated with poor outcomes having a 10 year all-cause mortality of 46.5%.12
MAC invades lung tissues, specifically macrophages, meaning that most antibiotics have limited efficacy against MAC as they penetrate macrophages poorly. Additionally, MAC shows a greater degree of resistance than other commonly occurring NTM strains.13 14 15 16 17 18 It is therefore imperative that macrolide monotherapy is avoided in patients who have MAC pulmonary disease as this is associated with the development of resistance.19
As stated previously, the drug management of macrolide-resistant MAC is analogous to that of MDR-TB.1 Combined with the worse treatment response rates and increased mortality associated with macrolide-resistant MAC strains,20 the importance of regularly testing patients at risk of MAC pulmonary disease should not be underestimated. By screening for all types of NTM, the species responsible for infection can be detected and appropriate guideline based therapy can be initiated. If, on the other hand, NTM can be ruled out, macrolide monotherapy could be prescribed, if appropriate, without fear of resistance developing.
Being aware of the presence of NTM MAC is of equal significance as, left untreated, MAC pulmonary disease is associated with a 5 year all-cause mortality of 33%, compared to 22% when treated.21 In the meantime, patients may experience a significant decline in health-related quality of life, with physical functioning, general health, social functioning, pain and energy all being affected by the disease.7
Testing for NTM.
Currently, sputum, induced sputum, bronchial washings and bronchoalveolar lavage fluid are used to detect NTM pulmonary disease. A patient must have two or more positive sputum samples of the same NTM species or one positive bronchial wash/lavage or compatible histopathological findings with one positive culture.19