Increasing incidence of Mycobacterium xenopi at Bellevue Hospital - An emerging pathogen or a product of improved laboratory methods?

Study objectives: To investigate the dramatic rise in number of Mycobacteri um xenopi isolates identified in our mycobacteriology laboratory, and to de termine if this increase was due to emerging clinical pathology or to chang es in culture technique. Design: Retrospective chart and laboratory review. Setting: University-affiliated tertiary-care city hospital. Patients: Eighty-one patients with a single culture positive for M xenopi f rom 1975 to 1994 (period 1), and 47 patients with two or more cultures posi tive from 1994 to 1998 (period 2). Interventions: The Bellevue mycobacteriology laboratory changed the culture medium from solid Lowenstein-Jensen medium (used from 1975 to 1990) to the Septi-Check AFB System (Becton-Dickinson; Glencoe, MD; used from 1991 to 1 994), to the Mycobacteria Growth Indication Tube (MGIT; Becton-Dickinson; u sed from 1995 to 1998). Measurements and results: We recovered 29 M xenopi isolates from 1975 to 19 90, 12 isolates from 1991 to 1994, and 381 isolates from 1995 to 1998, We s ubsequently identified and reviewed the medical records of all 81 patients who were culture positive for M xenopi from 1975 to 1994 (period 1), and 46 patients who had two or more isolates culture positive for M xenopi from 1 995 to 1998 (period 2), For period 1, 75% of the subjects were male, 80% we re minority, and at least 43% were HIV positive. Only one patient had clini cal M xenopi lung disease during this period. For period 2, 79% of the subj ects were male, 83% were minority, and at least 58% were HIV positive; two additional patients were identified who had clinical M xenopi lung disease. Conclusions: The dramatic increase in M xenopi isolates noted in our hospit al was due to a more sensitive laboratory isolation technique, rather than a true increase in clinical disease. Other hospitals utilizing MGIT systems for mycobacterial recovery should interpret positive M xenopi cultures wit h caution.