Infections with Nontuberculous Mycobacteria: Increased Awareness and Recent Developments

Abstract

Nontuberculous mycobacteria represent a multispecies and extremely heterogeneous group of environmental bacteria and include many species that can cause severe disease. Still, they are given little attention as pathogenic agents, when compared to Mycobacterium (M.) tuberculosis. Individuals at risk to become infected by NTM usually suffer from immune defects or underlying diseases such as cystic fibrosis or chronic obstructive pulmonary disease. Therapeutic immunosuppression is an additional cause for increased susceptibility, but healthy, apparently immunocompetent individuals may also develop disease. NTM infections can manifest as lung infections, lymphadenitis, skin, bone, and soft tissue infections, or disseminated disease. Pulmonary disease is worldwide most frequently caused by different species of the M. avium complex. M. abscessus causes serious lung infections in patients afflicted by cystic fibrosis. Diagnosis of the infection is frequently delayed because there are few specific symptoms, and cultivation of the infective agent from clinical samples is not always successful. Isolation of NTM from a patient’s lung, on the other hand, is no proof of infection, but might also result from colonization of the organ or from contamination with these ubiquitously occurring environmental bacteria. Therefore further diagnostic options have to be considered before initiating antibiotic intervention. NTM treatment is hampered by the high level of primary resistance against antibiotics, which culminates in the multidrug resistance of M. abscessus. New findings on infection rates, transmission routes, and nosocomial potential of NTM are currently changing our perception of the relevance of NTM infections. In the last two decades, an increase in NTM lung disease was reported in many regions of the world, which can be explained by demographic trends and medical progress prolonging life expectancy of persons vulnerable to NTM infections. Transmission of M. abscessus between patients with cystic fibrosis has challenged the hitherto commonly accepted classification of NTM as environmental non-transmissible infectious agents. And finally the incidence of severe and fatal nosocomial infections has increased attention for NTM. Studies on the burden of disease considering infection numbers, mortality rates, and treatment costs have further substantiated the significance of NTM infections for public health. In view of these new perspectives, a higher priority for NTM disease both in basic research and when deciding on public health measures is indicated.