Opportunist (environmental) mycobacterial diseases

Abstract 

Opportunist mycobacteria are low-grade pathogens, which transiently colonize the lung more often than they produce disease. Middle-aged and elderly patients with pre-existing lung disease and/or some compromise of immune function are particularly vulnerable. Symptoms and signs mainly reflect other underlying lung or cardiac conditions. Clinically and radiologically the diseases caused by the various species are indistinguishable from each other and from Mycobacterium tuberculosis. Diagnosis requires culture and special methods of identification, which nowadays include tests based on molecular biology. In vitro susceptibility testing, with the exception of M. kansasii, does not predict clinical response. Rifampicin and ethambutol exhibit synergy against opportunist mycobacteria and, together, comprise first-line treatment. M. kansasii can usually be cured by nine months’ therapy. For M. avium-intracellulare-scrofulaceum, M. malmoense and M. xenopi therapy is given for two years and will usually arrest disease, if not cure it. Death rates are high but only a small minority die because of the opportunist mycobacterial disease. Surgery has a place in those with unilateral disease who are not doing well on chemotherapy but who have sufficient cardiopulmonary reserve to permit thoracotomy and resection. HIV predisposes to these diseases but highly active anti-retroviral therapy has improved the prognosis for those with both diseases. Better antimycobacterial drugs are required, as well as improved understanding of the structural, physiological and immunological defects that may open the way for these diseases.

Keywords: ethambutol, HIV, immunotherapy, in vitro sensitivity testing, opportunist (environmental) mycobacteria, rifampicin, surgery