Non-tuberculous mycobacterial infections at San Francisco General Hospital

The epidemiology of non-tuberculous mycobacteria (NTM) infection is not well defined. We evaluated the trends in incidence of NTM infections at San Francisco General Hospital (SFGH), a large metropolitan county hospital.

We performed a retrospective review of microbiologic and clinical records of all patients with a positive NTM culture reported from 1993 to 2001. NTM infection was defined by the isolation of >1 NTM from any clinical specimen. Patients were stratified by human immunodeficiency virus (HIV) status. Univariate and multivariate logistic regression were used to identify factors that were independently associated with NTM infection. Trends over time were assessed using Poisson test for trend.

During the study period, 25 736 samples from 7395 patients were cultured for mycobacteria. Of these samples, 2853 (11.1%) from 1345 patients (18.2%) were culture positive for NTM. Patient characteristics associated with infection included younger age (P < 0.001), male gender (P < 0.001), White ethnicity compared with Asian and Hispanic (P < 0.001 and P = 0.01, respectively), and HIV positivity (P < 0.001). Overall, NTM infection at SFGH decreased significantly from 319 cases in 1993 to 59 in 2001 (P < 0.001). Mycobacterium avium was predominant in both HIV-positive and HIV-negative populations (74.5% and 44.6% of isolates, respectively), and Mycobacterium kansasii was the second most common NTM species isolated. The proportion of other NTM species isolated in these groups differed.

In contrast to other published studies, time-series analyses show that NTM isolation rates decreased during the study period at SFGH, where NTM was most strongly associated with HIV infection.