A decade surveillance study of Mycobacterium xenopi disease and antimicrobial susceptibility levels in a reference teaching hospital of northern Italy:: HIV-associated versus non-HIV-associated infection

Objective and Method: The aim of our survey is to investigate the epidemiology and in vitro antimicrobial susceptibility levels of 35 consecutive Mycobacterium xenopi strains responsible for confirmed disease at a University Hospital from 1993 to 2002 and to identify eventual differences in the in vitro sensitivity profile between the 17 strains isolated from patients with HIV disease and the 18 isolates cultured from non-HIV-infected individuals. Results: The involvement of lower airways accounted for 88.6% of cases; but atypical pulmonary findings, including cavitation and a prominent inflammatory reaction, recently emerged in HIV-infected patients successfully treated with HAART, which raises the possible role of immune reconstitution syndrome in the clinical pathomorphism of this opportunistic disease. When compared with non-HIV-infected patients, patients with HIV disease had a lower mean age and a tendency to suffer from late relapses. The greatest overall in vitro sensitivity rate was registered for capreomycin and protionamide (100% of strains) followed by kanamicin (96.6%), whereas susceptibility rates for the first-line compounds such as ethambutol, isoniazid, and rifampicin were slightly lower (85.7% to 91.4%). No temporal variation in the susceptibility index was seen over the study decade. Non-HIV-infected patients experienced a higher frequency of M. xenopi isolates that proved to be resistant to at least one tested compound compared with HIV-associated episodes, despite the heavy and prolonged exposure of HIV-infected patients to broad spectrum antimicrobials, which included agents effective on atypical mycobacteria. Only one HIV-positive patient developed rifampicin resistance in his third disease recurrence. Conclusion: A rapid diagnosis, a reliable differentiation between colonization and disease, and an optimal therapeutic choice for atypical mycobacterial disease (including M. xenopi one) are still serious challenges for clinicians and bacteriologists who treat immunocompromised patients, such as those with HIV disease. In the immunocompromised host, diagnostic difficulties posed by late identification and eventually concurrent opportunistic disorders add their negative effects to therapeutic problems due to the unpredictable in vitro susceptibility profile of atypical mycobacteria, such as M. xenopi.