Synopsis
Determine whether an environmental mycobacterial isolate represents pulmonary, disseminated, device-related or cutaneous disease; exclude tuberculosis first; and select a species- and susceptibility-led multidrug plan with the monitoring needed for prolonged toxic therapy.
- An acid-fast smear is not a species result. Use M tuberculosis molecular testing and culture before relaxing infection control or applying an NTM label.
- For pulmonary disease, combine symptoms, characteristic CT and reproducible microbiology; one low-burden sputum isolate can be contamination or transient carriage.
- Two separate sputum cultures growing the same species strengthen pulmonary causality; one positive bronchoscopic sample or compatible biopsy can satisfy the microbiological component in the right syndrome.
Key red flags
Upper-lobe cavities, pleural thickening, haemoptysis and weight loss resemble tuberculosis or chronic fungal disease and usually justify faster specialist assessment.
Investigation priorities
Demonstrate reproducible pulmonary isolation and quantify organism burden before treatment.
Management branches
A respiratory smear or culture reports acid-fast mycobacteria before species is known.
- Review TB epidemiology, symptoms and imaging and maintain the local airborne pathway when pulmonary TB remains plausible.
- Request rapid M tuberculosis complex testing and retain cultures for definitive species and susceptibility rather than assuming the smear is TB or NTM.
Key medicines
Daily triple regimen for severe macrolide-susceptible pulmonary MACGive rifampicin 600 mg daily, ethambutol 15 mg/kg daily and azithromycin 250 mg daily or clarithromycin 500 mg twice daily.
Intermittent triple regimen for selected non-severe pulmonary MACGive rifampicin 600 mg, ethambutol 25 mg/kg and azithromycin 500 mg or clarithromycin 1 g in two divided doses three times weekly.