Disseminated Mycobacterium genavense infection: clinical and microbiological features and response to therapy.

Objective: Mycobacterium genavense is a newly described pathogen that causes disseminated infection in AIDS. It is difficult to detect and identify due to its slow growth and fastidious nature. There is little information available about therapy for this new pathogen. We describe clinical and laboratory features and response to therapy in four patients with advanced AIDS complicated by disseminated M. genavense infection from Denver, Colorado, USA.

Design And Methods: Retrospective analysis of four cases identified in an AIDS clinic affiliated with a municipal hospital in Denver, Colorado. Clinical samples were inoculated onto BACTEC 12B, Lowenstein-Jensen, and Middlebrook 7H11 media.

Results: The clinical features mimicked those of disseminated M. avium complex infection, with invasion of liver, spleen and lymph nodes with acid-fast bacilli (AFB). Acid-fast smears of blood and lymph nodes were positive; there was a modest increase in the growth index in BACTEC broth and tiny colonies appeared on Middlebrook agar. Patients were treated with combinations of antimycobacterial agents. Blood smears and cultures reverted to negative in treated patients. The best clinical response was associated with clarithromycin therapy.

Conclusions: Disseminated disease due to M. genavense should be suspected among patients with the clinical presentation of disseminated M. avium complex infection and low growth index on BACTEC cultures for AFB. The diagnosis of M. genavense may be facilitated by performing acid-fast stains of samples from BACTEC bottles in such individuals. Clarithromycin therapy is associated with clinical improvement and clearance of bacteremia.