Diagnostics
The diagnosis of NTM is delayed for several reasons. One is the lack of awareness among clinicians about NTM and its risk factors, including hobbies such as gardening or working in places where dirt is aerosolized, such as on road crews, or even from hot tubs. A thorough history is critical.
Another is not recognizing the need for an acid-fast bacilli (AFB) culture, which requires specialized media. Fortunately, NTM can be picked up on fungal cultures, Dr. Cannella noted. Clinicians are sometimes discouraged from culturing AFB because doing so may not be cost-effective. And many hospital laboratories are increasingly sending cultures to outside labs, and it can take days – sometimes even more than a week – to receive a report of results.
Charles Daley, MD, chief of the Division of Mycobacterial and Respiratory Infections at National Jewish Health, expressed his frustration about labs in an interview, saying diagnostics is “an important hole in the U.S., as our laboratories do not provide clinicians with the results that they need to make good decisions. Most laboratories in the U.S. just don’t speciate the organisms or subspeciate in the setting of abscesses. They don’t tell the clinician enough about the susceptibility, particularly whether there’s inducible resistance. As a clinician, you just don’t have the information to make the right decisions. ... We need to improve diagnostics in NTM. Everything is there and available. They just don’t want to do it because it increases the costs.”
Men tend to have fibrocavitary disease, which shows on ordinary chest x-rays, but CT scans are essential for women because women tend to have either nodular disease or bronchiectasis, which does not show on a plain film.
Treatment
A standard treatment for NTM lung disease includes three or four medications – clarithromycin or azithromycin, rifampin or rifabutin, ethambutol, and streptomycin or amikacin. In vitro resistance is important in predicting the clinical response to a macrolide or amikacin.
For bronchiectatic disease, National Jewish Hospital recommends treatment three times per week rather than daily therapy, as it is better tolerated. Azithromycin is preferred over clarithromycin. Amikacin should be added if there is cavitary or severe disease, and the macrolide is then given daily.
Dr. Olivier suggested that physicians stagger the initiation of those drugs to improve the tolerability of the difficult regimen. Generally, treatment is for 18 months – a year after sputum cultures become negative.
If therapy fails – that is, sputum is persistently positive at 6 months – amikacin liposomal inhalation solution (Arikayce) is likely to be added. Patients should be monitored with monthly safety labs, sputum cultures, and an audiogram (if receiving amikacin). Every 3 months, vestibular tests, eye exams, and spirometry should be conducted, and every 6 months, physicians should order a CT, an audiogram, and an electrocardiogram.
Despite completing such a rigorous regimen, about half of patients experience reinfection because of their underlying host susceptibility. Genomic sequencing shows that these are new infections, not relapses, Dr. Prevots said. She also noted that gastroesophageal reflux disease is a significant risk factor because of chronic aspiration.
Dr. Daley outlined the newer treatments being studied. They include Arikayce, omadocycline, and bedaquiline. He added, “There’s a neutrophil elastase inhibitor trial that’s ongoing, a huge trial. There’s another one looking at basically eosinophilic inflammation.”
Other trials are in the offing, he said, all focusing on the inflammatory response – a development he described as exciting, because for the longest time, there were few if any NTM trials.
Dr. Cannella is also buoyed by the potential synergy of dual beta-lactam therapy with ceftaroline and a carbapenem for M abscessus infections, which are notoriously difficult to treat.
There are unique problems facing drug development for NTM because, for approval, the U.S. Food and Drug Administration requires the drug to “improve how a patient feels, functions, or survives.” NTM is associated with low mortality, so that “is off the table,” Dr. Daley explained. It’s hard to quantify improvement in function. The top two symptoms to measure are coughing and fatigue, he said. But both are difficult to measure, and some of the medicines worsen cough. Some research groups are now trying to validate patient-reported outcome instruments to satisfy the FDA’s requirements.