Non-Tuberculous Mycobacteria: Seven-Year Experience of a Tertiary Hospital

Non-tuberculous mycobacteria are ubiquitous organisms. Precise determination of infection numbers is difficult, since reporting them to public health departments is frequently not mandatory; furthermore, isolating a non-tuberculous mycobacteria does not necessarily translate into disease. The aims of this study were to ascertain non-tuberculous mycobacteria data of a tertiary hospital, determine the incidence and approach to colonization versus disease, and the incidence of predisposing comorbidities.

Retrospective study in a tertiary hospital, involving patients with positive cultural exam for non-tuberculous mycobacteria in any biological sample, from 2010 to 2017.

A total of 125 non-tuberculous mycobacteria isolates was identified, corresponding to 96 patients. Of these, 57.4% were male (n = 54); median age was 65 years (interquartile range = [50 - 82]). From these, 60.7% (n = 57) had some degree of immunosuppression, most frequently due to malignant tumour (49.0%) or HIV infection (39.2%). It was found that 29 patients (31.0%) had structural respiratory tract changes. Colonization was defined in 65.6% of patients (n = 63). While 71.0% of non-tuberculous mycobacteria infections were pulmonary, the remaining 29.0% presented as disseminated. According to available clinical records, 60.6% (n = 20) of the presumably infected patients fulfilled American Thoracic Society diagnostic criteria for non-tuberculous mycobacteria disease.

Several cases of non-tuberculous mycobacteria infection in this study presented as life-threatening, multi-systemic disease, highlighting the importance of accurate diagnosis and timely treatment. Other cases of presumed infection might instead have corresponded to colonization, possibly resulting in futile therapy.

While there are diagnostic criteria for treatment of non-tuberculous mycobacteria infections, no such guidelines exist to assess colonization. One of the most challenging aspects remains the correct differentiation between colonization and early-stage infection.