Nontuberculous mycobacterial infections in a Danish region between 2011 and 2021: evaluation of trends in diagnostic codes

Nontuberculous mycobacteria (NTM) are emerging as human pathogens at increasing rates. In Denmark, few studies of NTM exist, but these have not been able to confirm an increasing trend. Existing studies have not utilised clinical data or investigated geographical variations.A retrospective cohort study of patients with an ICD-10 diagnostic code of NTM infection in a Danish region, Central Denmark Region, between 2011 and 2021. Incidence rates per 100,000 citizens were calculated using data from Statistics Denmark. A Spearman's rank correlation coefficient was computed to assess the linear relationship between years and annual incidence rates.We identified 265 patients, 53.2% (n = 141) females, with a median age of 65.0 years (IQR 47-74). The age distribution was bimodal with peaks in extreme age groups between 0-14 years of age (n = 35, 13.2%) and above 74 years (n = 63, 23.8%). Most patients were coded with a pulmonary infection (51.3%, n = 136), 35.1% (n = 93) with other/unspecified infection and 13.6% (n = 36) with a skin infection. Incidence rates ranged from 1.3 (2013) to 2.5 (2021) per 100,000 citizens. There was a highly positive linear correlation of NTM incidence rates over the years (r = 0.75, p = 0.010) suggesting an increasing trend.More than one-third with an NTM infection based on ICD-10 codes were found in extreme age groups. At least half of the patients had a pulmonary infection. Contradicting previous data from Denmark, we found an increasing trend of NTM, potentially suggesting an increase in clinically relevant disease, a higher awareness and test rate, or improved coding.