Characteristics of Nontuberculous Mycobacterial Infections at a Midwestern Tertiary Hospital: A Retrospective Study of 365 Patients

Abstract

Background: The prevalence of infections due to nontuberculous mycobacteria (NTM) is increasing worldwide, yet little is known about the epidemiology and pathophysiology of these ubiquitous environmental organisms. Pulmonary disease due to Mycobacterium avium complex is most prevalent, but many other NTM species can cause disease in virtually any organ system. As NTM becomes an increasingly common cause of morbidity and mortality, more information is needed about the epidemiology of NTM disease.

Methods: We conducted a retrospective chart review of all patients with cultures that grew NTM at a Midwestern tertiary hospital from 1996 to 2017. Information on demographics, medical history, clinical findings, treatment, and outcome was obtained from medical records of all NTM isolates. American Thoracic Society/Infectious Diseases Society of America criteria were used to define pulmonary NTM infections.

Results: We identified 1064 NTM isolates, 365 of which met criteria for NTM infection. Pulmonary cases predominated (185 of 365; 50.7%), followed by skin/soft tissue (56 of 365; 15.3%), disseminated (40 of 365; 11%), and lymphatic (28 of 365; 7.7%) disease. Mycobacterium avium complex was the most common species (184 of 365; 50.4%). Individuals aged >50 years were most affected (207 of 365; 56.7%). Common comorbidities included structural lung disease (116 of 365; 31.8%), use of immunosuppressive medications (78 of 365; 21.4%), malignancy (59 of 365; 16.2%), and human immunodeficiency virus (42 of 365; 11.5%).

Conclusions: This large cohort provides information on the demographics, risk factors, and disease course of patients with pulmonary and extrapulmonary NTM infections. Most patients had medical comorbidities that resulted in anatomic, genetic, or immunologic risk factors for NTM infection. Further population-based studies and increased disease surveillance are warranted to further characterize NTM infection prevalence and trends.

Keywords: atypical mycobacteria; nontuberculous mycobacteria.

Figure 1.

Flowchart of patient selection. A logging system containing the medical record numbers of all patients between 1996 and 2017 at the University of Iowa Hospitals and Clinics with cultures positive for Mycobacterium tuberculous or nontuberculous mycobacteria (NTM) was reviewed. Medical record review was performed on all patients with cultures positive for NTM or Mycobacterium bovis. Infection was defined using the American Thoracic Society/Infectious Diseases Society of America (ATS/IDSA) NTM lung disease guidelines. Contaminant was defined as a single positive culture without clinical or radiographic evidence of disease. Colonization was defined as ≥2 positive cultures without clinical or radiographic evidence of disease. Cases were excluded if medical records lacked sufficient information to diagnose infection according to ATS/IDSA guidelines. Cases of chronic NTM infection with multiple positive cultures were included only once in data analysis.