ORIGINAL RESEARCH Epidemiological, clinical and therapeutic features of AIDS-related Mycobacterium kansasii infection during the HIV pandemic: an 11-year follow-up study R Manfredi, 1 A Nanetti, 2 R Valentini, 2 M Ferri, 2 S Morelli, 2 and L Calza 1 1 Division of Infectious Diseases, and 2 Division of Microbiology, Department of Clinical and Experimental Medicine, University of Bologna, ‘Alma Mater Studiorum’, Bologna, Italy Objectives Optimal diagnosis and timely treatment of atypical mycobacteriosis, and especially Mycobacterium kansasii disease, remain a serious challenge for clinicians engaged in the management of the immunocompromised host. Methods and Results From more than 2700 hospitalizations (over 1800 patients) attributable to HIV-associated disorders over an 11-year period, 12 patients were found to have a confirmed M. kansasii infection. This reflects the recent reduction in the frequency of this HIV-related complication, which virtually disappeared after the introduction of potent antiretroviral combinations in 1996. In the early 1990s, the lack of effective antiretroviral regimens made frequent the association with AIDS, a mean CD4 lymphocyte count of nearly 20 cells/mL, and an extremely variable chest X-ray features. The recent detection of a further case was attributable to late recognition of very advanced HIV disease, complicated by multiple opportunistic disorders. Conclusions Mycobacterium kansasii respiratory or disseminated infection continues to occur, and poses diagnostic problems in terms of late or missed identification as a result of slow culture and frequently concurrent opportunistic disease. Serious therapeutic difficulties also arise from the unpredictable in vitro antimicrobial susceptibility profile of these organisms, and from the need to start an effective combination therapy that does not interfere with other medications as soon as possible. Keywords: antimicrobial resistance, antiretroviral therapy, clinical features, epidemiology, HIV infection, Mycobacterium kansasii Received: 15 January 2004, accepted 24 May 2004 Introduction A typical mycobacteriosis is an AIDS-defining disease. Such diseases characterize the most advanced phases of HIV-related immunodeficiency, with CD4 lymphocyte counts o100 cells/mL. However, the incidence of atypical mycobacteriosis showed a sharp drop after the introduction in mid-1996 of potent antiretroviral combinations [highly active antiretroviral therapy (HAART)] [1,2]. Mycobacterium kansasii was considered an infrequent human pathogen of environmental origin in the pre-AIDS era [3–5], but was subsequently increasingly seen to be responsible for respiratory and/or disseminated infection in patients with HIV disease [3,6–8]. In HIV-infected patients, colonization of the respiratory and enteric tracts by M. kansasii may be common, and M. kansasii may also be responsible for disseminated infection [3] and rare focal disease localization, such as septic arthritis [5] and pericarditis [9]. The frequency of M. kansasii infection in both HIV-infected patients and the general non-HIV- infected population has remained lower than that of Mycobacterium avium-intracellulare, although fatal cases, often attributable to multiresistant strains, have been Correspondence: Dr Roberto Manfredi, Dipartimento di Medicina Clinica Specialistica e Sperimentale, Sezione di Malattie Infettive, Universita ` di Bologna ‘Alma Mater Studiorum’ Ospedale S. Orsola, Via Massarenti 11, I-40138 Bologna, Italy. Tel: 1 39 051 63 63 355; fax: 1 39 051 34 35 00; e-mail: manfredi@med.unibo.it r 2004 British HIV Association HIV Medicine (2004), 5, 431–436 431