title: Incidence and clinical implications of isolation of Mycobacterium kansasii: results of a 5-year, population-based study.
abstract: 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.
  
  
  METHODS
  Population-based laboratory surveillance.
  
  
  METHODS
  Three counties in northern California.
  
  
  METHODS
  All persons who had a positive culture for M. kansasii between 1 January 1992 and 31 December 1996.
  
  
  METHODS
  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.
authors.affiliation: University of California, San Francisco, 94143, USA.
authors.forename: K C
authors.initials: KC
authors.lastname: Bloch
authors.forename: L
authors.initials: L
authors.lastname: Zwerling
authors.forename: M J
authors.initials: MJ
authors.lastname: Pletcher
authors.forename: J A
authors.initials: JA
authors.lastname: Hahn
authors.forename: J L
authors.initials: JL
authors.lastname: Gerberding
authors.forename: S M
authors.initials: SM
authors.lastname: Ostroff
authors.forename: D J
authors.initials: DJ
authors.lastname: Vugia
authors.forename: A L
authors.initials: AL
authors.lastname: Reingold
mesh_terms: D017088:AIDS-Related Opportunistic Infections / Q000453:epidemiology*; D000328:Adult; D000368:Aged; D002140:California / Q000453:epidemiology; D016009:Chi-Square Distribution; D002675:Child, Preschool; D015897:Comorbidity; D005260:Female; D018023:HIV Seronegativity; D006679:HIV Seropositivity / Q000453:epidemiology* / Q000382:microbiology; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D009165:Mycobacterium Infections, Nontuberculous / Q000453:epidemiology*; D019909:Mycobacterium kansasii / Q000302:isolation & purification*; D011159:Population Surveillance; D012141:Respiratory Tract Infections / Q000453:epidemiology*; D012959:Socioeconomic Factors; D018709:Statistics, Nonparametric