From the Guidelines
Quantifying positive in MAI typically requires at least two separate expectorated sputum samples with positive culture results or one positive bronchial wash or lavage culture, as stated in the American Journal of Respiratory and Critical Care Medicine 1.
Importance of Quantification
This quantification is crucial because MAI organisms can sometimes be isolated from respiratory specimens without causing actual disease, particularly in patients with underlying lung conditions.
- The presence of MAI in respiratory specimens does not always indicate disease, as it can be a contaminant or a colonizer.
- Treatment should only be initiated when there is clear evidence of disease rather than mere colonization, to prevent unnecessary antibiotic exposure and potential side effects.
Diagnostic Criteria
The diagnostic criteria for MAI pulmonary disease include:
- Positive culture results from at least two separate expectorated sputum samples
- Positive culture result from at least one bronchial wash or lavage
- Transbronchial or other lung biopsy with mycobacterial histopathologic features and positive culture for NTM
Treatment Considerations
The standard treatment regimen for MAI includes a macrolide, ethambutol, and rifampin, typically continued for at least 12 months after culture conversion, as recommended by the New England Journal of Medicine 1.
- The choice of treatment regimen should be based on the pathogenic potential of the NTM isolate and the patient's clinical presentation.
- Expert consultation may be helpful in making treatment decisions, particularly in cases where the diagnosis is uncertain or the patient has a complex clinical presentation.
From the Research
Quantification of Positive Outcomes in MAI Treatment
- The study 2 found that treatment success, defined as 12 months of negative cultures while on therapy, was achieved in 59% of patients in regimen A, 55% in regimen B, and 65% in regimen C, with no statistically significant differences between the regimens.
- Another study 3 reported that among 187 patients who could be evaluated, blood cultures became negative more often in the three-drug group (69%) than in the four-drug group (29%), with a significant difference (P<0.001).
- The same study 3 also found that among patients treated for at least four weeks, bacteremia resolved more frequently in the three-drug group (78%) than in the four-drug group (40%), with a significant difference (P<0.001).
- A review of patient records 4 identified four distinct clinical patterns in 244 patients with true positive MAI infections, with varying treatment approaches and outcomes.
Treatment Approaches and Efficacy
- The study 5 recommended a treatment approach for disseminated MAC disease, including the use of at least two agents, with oral clarithromycin or azithromycin as the preferred first agent, and ethambutol as the most rational choice for the second agent.
- The study 6 evaluated the in vitro activities of various drug combinations against Mycobacterium avium and found that certain combinations, including those with clarithromycin and clofazimine, showed activity against all 10 MAC strains tested.
- The study 2 demonstrated the effectiveness of daily and three-times-weekly regimens containing azithromycin for the treatment of MAC lung disease, with treatment success rates ranging from 55% to 65%.
- The study 3 found that the median survival was 8.6 months in the three-drug group and 5.2 months in the four-drug group (P = 0.001), indicating a significant difference in survival outcomes between the two treatment regimens.