Background: NTM are uncommon causes of infection in SOT recipients but may cause significant morbidity and mortality.

Methods: A retrospective cohort of all patients who underwent a SOT in a tertiary teaching hospital between Jan. 1st 2004 and Dec. 31st 2013 with microbiology cultures for NTM post-transplant were identified and a medical record review performed. Diseased were classified as SOT recipients who met either 1) American Thoracic Society/IDSA criteria for NTM disease (for lung isolates) or 2) had an NTM cultured from a sterile site with a compatible clinical syndrome. The rest were classified as colonized.

Results:3338 SOT recipients were identified over 10 years. The most common organ transplanted was kidney (n=1720; 51.7%), followed by liver (n=766; 22%), lung (n=556; 16.6%) and heart (n=282 8.4%). NTM were isolated in 50 patients at a median 29.3 months of follow up. The majority (n= 43; 86 %) were lung transplant recipients. NTM patients were predominantly male (66%) with mean age 52.6 years (range 21-79). Most isolates were identified from the lungs (96 %) and one each from blood and wound cultures. The blood stream infection was treated as true disease while the wound culture was deemed a colonizer. Amongst the pulmonary NTM isolates 20/48 were treated for NTM (41.7%) although only 8 (16.6%) met ATS criteria for pulmonary disease. Among the colonized (n=40), isolation of the same species on multiple occasions was associated with treatment (8/12 (67%) who were treated had multiple positive cultures vs. 6/28 (21 %) who were not treated, P=0.014). There was no difference in the median time from transplant to first positive culture in the diseased (192 days, range 11-1785) compared to the colonized (133 days, range 19-1974; P=0. 295) M. avium complex (53.6 %) and M. fortuitum (12.1%) were the most common pathogens in colonized patients compared to M. avium complex (44%) and M. abscessus (22%) in the patients with disease. Of the 50 patients, four of the 9 patients died during the follow up period in the diseased vs. four of 41 amongst those colonized (P=0.026)

Conclusion: NTM disease is rare in SOT recipients but may be associated with post-transplant mortality. Repeated isolation of the same species of NTM from lung was associated with treatment irrespective of the ATS criterion. The ATS criterion for NTM pulmonary disease may need further validation in this immunosuppressed population.

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