Atypical Mycobacterial Infection.Care & specialists in Ireland

Atypical mycobacterial infection — also called non-tuberculous mycobacterial (NTM) infection — is a disease caused by environmental mycobacteria other than tuberculosis or leprosy. Mycobacterium avium complex causes over 80% of pulmonary cases. The organisms live in soil and water and infect humans through inhalation, aspiration, or direct skin inoculation.

Atypical mycobacterial infection is generally not contagious person-to-person, with the rare exception of suspected M. abscessus transmission between cystic fibrosis patients. NTM is acquired from environmental sources — soil, household water, hot tubs, and biofilms. Family members of patients are not at increased risk in everyday life.

Tuberculosis is caused by Mycobacterium tuberculosis, is highly contagious between humans, and is treated with 6 months of four-drug therapy. Atypical mycobacterial infection involves over 200 environmental species, is not contagious, and requires 12-24 months of species-specific therapy. Both can cause chronic cough and lung damage and may look similar on chest imaging.

NTM lung disease is acquired by inhaling aerosolized water or soil containing the organism. Showerhead biofilms, hot tubs, humidifiers, and household plumbing are common sources. Most exposure does not cause disease — bronchiectasis, COPD, postmenopausal female phenotype, cystic fibrosis, and immunosuppression are the main predispositions for environmental exposure to progress to disease.

Lady Windermere syndrome is the classic presentation of nodular bronchiectatic Mycobacterium avium complex disease in slim, postmenopausal women without major underlying lung disease. It is named after a fictional character thought to suppress coughing for social reasons. Imaging shows tree-in-bud nodules and bronchiectasis predominantly in the lingula and middle lobe.

Diagnosis requires compatible respiratory symptoms, characteristic findings on high-resolution CT chest, and positive NTM cultures from at least two separate sputum samples or one bronchoalveolar lavage. A single positive culture without symptoms or imaging changes is considered colonization. Species identification by molecular methods guides treatment.

Pulmonary NTM is treated for at least 12 months past culture conversion — typically 18-24 months total. Cervicofacial lymphadenitis in children often resolves with surgical excision alone. Skin and soft tissue infections require 4-6 months of combination antibiotics. M. abscessus disease may require even longer therapy with intravenous and inhaled drugs.

Cure rates depend on species and form. M. kansasii has cure rates above 90% with rifampin-based therapy. Macrolide-susceptible MAC achieves sustained culture conversion in 60-80% with the standard three-drug regimen. M. abscessus is the most difficult, with sustained conversion in 30-50%. Adherence and absence of macrolide resistance are the strongest predictors of cure.

Standard MAC treatment combines azithromycin, ethambutol, and rifampin. M. kansasii uses rifampin, ethambutol, and isoniazid or a macrolide. M. abscessus requires intravenous amikacin plus imipenem or cefoxitin and oral macrolides, tigecycline, or linezolid based on susceptibility. Inhaled amikacin liposome suspension is approved for refractory MAC.

Yes. Hot tub lung is a hypersensitivity pneumonitis or true NTM infection (most often M. avium complex) acquired by inhaling aerosolized hot tub water. Symptoms include cough, fever, and breathlessness developing weeks to months after exposure. Avoidance of the hot tub and treatment of the infection, sometimes with corticosteroids, leads to recovery.

Common side effects include ethambutol-induced optic neuritis with color vision loss, aminoglycoside-related hearing loss and kidney injury, rifampin-induced hepatitis and many drug interactions, macrolide-related QT prolongation, and clofazimine-induced orange-red skin discoloration. Regular monitoring by audiometry, ophthalmology, and bloods is essential during treatment.

Postmenopausal women, particularly slim women with scoliosis or pectus deformity, disproportionately develop nodular bronchiectatic MAC disease. The reasons are not fully understood but probably involve airway clearance mechanics, estrogen-related immunity changes, and subtle bronchiectasis. Men are more likely to have fibrocavitary disease related to COPD or prior tuberculosis.

Yes. Recurrence occurs in 30-40% of MAC patients over 5 years. Many recurrences are reinfections from environmental sources rather than relapses of the original strain, as shown by molecular typing. Reducing ongoing environmental exposure and maintaining good airway clearance lowers recurrence risk.

Buruli ulcer is a specific NTM skin infection caused by Mycobacterium ulcerans. It causes painless, slowly enlarging skin ulcers, predominantly on the limbs, in tropical regions of West Africa, Australia, and Latin America. WHO recommends combination rifampin and clarithromycin for 8 weeks, often with wound care or surgical excision.

Routine residential water testing is not recommended in most cases because NTM is ubiquitous in household water systems and a positive test does not predict infection. For severely immunocompromised patients or those with persistent NTM despite environmental modification, point-of-use filters and shower disinfection may be considered with specialist input.

Yes. Chronic pulmonary NTM disease frequently causes unintentional weight loss of 5-10% of body weight over months, along with fatigue, night sweats, and chronic cough. Low body mass index is a known risk factor for nodular bronchiectatic MAC and is associated with worse outcomes. Nutritional support is an important component of treatment.

Yes, although pulmonary NTM is rare in children. The most common pediatric NTM presentation is painless cervicofacial lymphadenitis in children aged 1-5, usually caused by M. avium complex. Complete surgical excision is curative in over 90% of cases. Pulmonary NTM in children almost always reflects underlying cystic fibrosis or immunodeficiency.

Surgical resection of localized cavitary or nodular disease is considered in patients with refractory or M. abscessus pulmonary disease, raising sustained culture conversion to 70-90% in selected cases. Surgical excision is the primary treatment for cervicofacial lymphadenitis in children and a useful adjunct to antibiotics in skin and soft tissue NTM.

NTM is identified in 5-30% of cystic fibrosis patients, with M. abscessus being especially difficult to eradicate. CF Foundation guidance recommends annual sputum NTM cultures, prolonged intensive multi-drug therapy when infection is established, and integration of NTM management within the CF center.