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Incidence and clinical implications of isolation of Mycobacterium kansasii: results of a 5-year, population-based
K C Bloch1, L Zwerling, M J Pletcher
1University of California, San Francisco, 94143, USA.
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.
Insights
Mycobacterium kansasii infections are more frequent in individuals with HIV/AIDS. Despite this, most patients show infection evidence, with HIV-positive individuals experiencing higher hospitalization rates and organism burden.
Area of Science:
- Infectious Diseases
- Epidemiology
- Public Health
Background:
- Mycobacterium kansasii, historically an uncommon pathogen, is increasingly identified in HIV-infected individuals.
- Limited understanding exists regarding the epidemiology and clinical impact of M. kansasii during the AIDS era.
Purpose of the Study:
- To compare the incidence, demographics, and clinical presentations of M. kansasii infections.
- To differentiate between HIV-positive and HIV-negative patient populations.
Main Methods:
- Population-based laboratory surveillance conducted in three Northern California counties.
- Analysis of M. kansasii positive cultures from January 1992 to December 1996.
- Calculation of cumulative incidence rates and linkage with 1990 U.S. Census data for demographic and socioeconomic analysis.
Main Results:
- 270 M. kansasii cases identified; 69.3% were HIV-positive.
- Higher incidence rates observed in HIV-positive (115/100,000) and AIDS patients (647/100,000) compared to the general adult population (2.4/100,000).
- HIV-positive patients showed increased rates of mycobacteremia (9.6% vs 0%), hospitalization (77.4% vs 51.9%), and smear positivity (41.7% vs 20.7%). Lower socioeconomic status indicators were prevalent.
Conclusions:
- M. kansasii isolation is more prevalent in HIV-positive individuals.
- Most patients exhibit clinical and radiologic signs of infection, irrespective of HIV status.
- HIV-M. kansasii co-infection is associated with higher hospitalization rates and organism burden, with poverty potentially influencing transmission.
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