INCIDENCE AND CLINICAL IMPLICATIONS OF ISOLATION OF MYCOBACTERIUM-KANSASII - RESULTS OF A 5-YEAR, POPULATION-BASED STUDY

Background: Mycobacterium kansasii, an unusual pathogen in the pre-AID S era, is increasingly reported to cause infection among patients with HIV infection. Little is known about the epidemiology and clinical im plications of M. kansasii infection in the AIDS era. Objective: To com pare the incidence, demographic characteristics, and clinical features of M. kansasii infection in HIV-positive and HIV-negative persons. De sign: Population-based laboratory surveillance. Setting: Three countie s in northern California. Patients: All persons who had a positive cul ture for M. kansasii between 1 January 1992 and 31 December 1996. Meas urements: Cumulative incidence rates were calculated for each year by dividing the number of adult patients by the annual estimated adult po pulation. Demographic and socioeconomic data for a single county were obtained by linkage with the 1990 U.S. Census report. Results: 270 pat ients (69.3% of whom were HIV positive) were identified, for an incide nce of 2.4 cases per 100 000 adults per year (95% Cl, 2.1 to 2.7), 115 cases per 100 000 HIV-positive persons per year (Cl, 99 to 133), and 647 cases per 100 000 persons with AIDS per year (Cl, 554 to 751). Ind icators of lower socioeconomic status were common among patients: Medi an incomes were $32 317 in census tracts in which cases were identifie d and $38 048 in census tracts without cases (P = 0.001), and 35.7% of patients had unstable housing situations. Ninety-four percent of case s were from respiratory isolates, and 87.5% of patients had evidence o f infection. Persons with HIV infection differed from those without HI V infection with respect to mycobacteremia (9.6% compared with 0%; P = 0.001), need for hospitalization (77.4% compared with 51.9%; P < 0.00 1), and smear positivity (41.7% compared with 20.7%; P = 0.005). Chron ic diseases were common among HIV-negative persons; however, 40.3% had no predisposing medical condition. Conclusions: Mycobacterium kansasi i isolation is more common in HIV-positive persons, but most patients with M. kansasii infection have clinical and radiologic evidence of in fection regardless of HIV status. Persons infected with HIV and M. kan sasii have a higher rate of hospitalization and a greater burden of or ganisms. A possible association with poverty suggests mechanisms of tr ansmission and requires further study.