Risk factors for transmission of Mycobacterium tuberculosis from HIV-infected tuberculosis patients, Botswana
DESIGN: Transmission was studied in 210 children aged <10 years (contacts) of unknown HIV status exposed to 51 adults with tuberculosis (index cases), including 41/49 (83.7%) with HIV infection.
METHODS: Data collected on index cases included demographics, clinical and social characteristics, sputum, HIV, and CD4 lymphocyte results. Tuberculin skin testing was performed on contacts, and their parent or guardian was interviewed. A positive test was defined as ≥10 mm induration. Skin test results were compared with results obtained from a population survey of children of similar age from the same community.
RESULTS: A positive skin test was found in 12.1% of exposed children compared with 6.2% in the community (P = 0.005). Of the infected children, 22 (78.6%) were contacts of a close female relative. The risk of transmission increased with the degree of sputum smear positivity for acid-fast bacilli among female index cases (10.8% if smear 0+, 9.3% if smear 1+, 29.4% if smear 2+, 44% if smear 3+, P < 0.001). In multivariate analysis, severe immunodeficiency (CD4 lymphocyte count <200 cells/mm3) among HIV-infected index cases was protective against transmission (OR 0.08, 95%CI 0.01–0.5, P = 0.006).
CONCLUSION: The intensity of exposure to tuberculosis patients and the degree of sputum smear positivity for acid-fast bacilli remain important risk factors for transmission of M. tuberculosis during the era of HIV. However, tuberculosis patients with advanced AIDS may be less infectious than patients in earlier stages of AIDS.
Document Type: Regular Paper
Affiliations: 1: The BOTUSA Project, Gaborone, Botswana 2: Division of TB Elimination, Centers for Disease Control and Prevention, Atlanta, Georgia, USA 3: Department of Nursing, University of Botswana, Gaborone, Botswana 4: National TB Reference Laboratory, Ministry of Health, Gaborone, Botswana 5: Epidemiology Unit, Ministry of Health, Gaborone, Botswana
Publication date: October 1, 2002
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