Increasing Incidence of Mycobacterium xenopi at Bellevue Hospital

To investigate the dramatic rise innumber of Mycobacterium xenopi isolates identified inour mycobacteriology laboratory, and to determine if this increase wasdue to emerging clinical pathology or to changes in culturetechnique. Retrospective chart and laboratoryreview. University-affiliated tertiary-carecity hospital. Eighty-one patients with asingle culture positive for M xenopi from 1975 to 1994(period 1), and 47 patients with two or more cultures positive from1994 to 1998 (period 2). The Bellevuemycobacteriology laboratory changed the culture medium from solidLowenstein-Jensen medium (used from 1975 to 1990) to the Septi-CheckAFB System (Becton-Dickinson; Glencoe, MD; used from 1991 to 1994), tothe Mycobacteria Growth Indication Tube (MGIT; Becton-Dickinson; usedfrom 1995 to 1998). Werecovered 29 M xenopi isolates from 1975 to 1990, 12isolates from 1991 to 1994, and 381 isolates from 1995 to 1998. Wesubsequently identified and reviewed the medical records of all 81patients who were culture positive for M xenopi from1975 to 1994 (period 1), and 46 patients who had two or more isolatesculture positive for M xenopi from 1995 to 1998 (period2). For period 1, 75% of the subjects were male, 80% were minority,and at least 43% were HIV positive. Only one patient had clinicalM xenopi lung disease during this period. For period 2,79% of the subjects were male, 83% were minority, and at least 58%were HIV positive; two additional patients were identified who hadclinical M xenopi lung disease. The dramatic increase in Mxenopi isolates noted in our hospital was due to a moresensitive laboratory isolation technique, rather than a true increasein clinical disease. Other hospitals utilizing MGIT systems formycobacterial recovery should interpret positive Mxenopi cultures with caution.