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Incidence and Clinical Implications of Isolation of Mycobacterium kansasii: Results of a 5-Year, Population-Based Study

Karen C. Bloch, MD, MPH; Lisa Zwerling, MD, MPH; Mark J. Pletcher, MD, MPH; Judith A. Hahn, MA; Julie L. Gerberding, MD, MPH; Stephen M. Ostroff, MD; Duc J. Vugia, MD, MPH; and Arthur L. Reingold, MD
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For author affiliations and current author addresses, see end of text. Acknowledgments: The authors thank Gretchen Rothrock of the California Emerging Infections Program for her help in organizing this study. They also thank Sally Liska and Anna Babst (San Francisco County), Miriam Valesco and Pat Dadone (Alameda County), and Rodney Smith (Contra Costa County) from the Department of Public Health Laboratories for allowing access to microbiological data. Grant Support: By a cooperative agreement with the Centers for Disease Control and Prevention. Dr. Bloch was supported by a National Institute of Mental Health Traineeship in AIDS Prevention Studies (MH 19105) and a National Institute of Mental Health Center grant (MH 42459). Requests for Reprints: Karen C. Bloch, MD, MPH, Division of Infectious Diseases, Vanderbilt University School of Medicine, A-3310 MCN, Nashville, TN 37212. Current Author Addresses: Dr. Bloch: Division of Infectious Diseases, Vanderbilt University Medical Center, A-3310 MCN, Nashville, TN 37212.

Copyright ©2004 by the American College of Physicians

Ann Intern Med. 1998;129(9):698-704. doi:10.7326/0003-4819-129-9-199811010-00004
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Background: Mycobacterium kansasii, an unusual pathogen in the pre-AIDS era, is increasingly reported to cause infection among patients with HIV infection. Little is known about the epidemiology and clinical implications of M. kansasii infection in the AIDS era.

Objective: To compare the incidence, demographic characteristics, and clinical features of M. kansasii infection in HIV-positive and HIV-negative persons.

Design: Population-based laboratory surveillance.

Setting: Three counties in northern California.

Patients: All persons who had a positive culture for M. kansasii between 1 January 1992 and 31 December 1996.

Measurements: Cumulative incidence rates were calculated for each year by dividing the number of adult patients by the annual estimated adult population. Demographic and socioeconomic data for a single county were obtained by linkage with the 1990 U.S. Census report.

Results: 270 patients (69.3% of whom were HIV positive) were identified, for an incidence of 2.4 cases per 100 000 adults per year (95% CI, 2.1 to 2.7), 115 cases per 100 000 HIV-positive persons per year (CI, 99 to 133), and 647 cases per 100 000 persons with AIDS per year (CI, 554 to 751). Indicators of lower socioeconomic status were common among patients: Median incomes were $32 317 in census tracts in which cases were identified and $38 048 in census tracts without cases (P = 0.001), and 35.7% of patients had unstable housing situations. Ninety-four percent of cases were from respiratory isolates, and 87.5% of patients had evidence of infection. Persons with HIV infection differed from those without HIV infection with respect to mycobacteremia (9.6% compared with 0%; P = 0.001), need for hospitalization (77.4% compared with 51.9%; P < 0.001), and smear positivity (41.7% compared with 20.7%; P = 0.005). Chronic diseases were common among HIV-negative persons; however, 40.3% had no predisposing medical condition.

Conclusions: Mycobacterium kansasii isolation is more common in HIV-positive persons, but most patients with M. kansasii infection have clinical and radiologic evidence of infection regardless of HIV status. Persons infected with HIV and M. kansasii have a higher rate of hospitalization and a greater burden of organisms. A possible association with poverty suggests mechanisms of transmission and requires further study.


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Figure 1.
Map of San Francisco, California, showing geographic distribution of patients with Mycobacterium kansasii infection by HIV status and median household income of census tract.

Gridlines delineate the 152 census tracts in San Francisco County. Shaded areas indicate census tracts with a median income of less than $20 000. Black circles represent HIV-positive patients, and white circles represent HIV-negative patients.

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