Free Content Changing prevalence of tuberculosis infection with increasing age in high-burden townships in South Africa

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Abstract:

SETTING: Crowded townships of Cape Town, South Africa, where human immunodeficiency virus (HIV) prevalence and tuberculosis (TB) notification rates are among the highest in the world.

OBJECTIVES: To determine age-specific prevalence rates of latent tuberculosis infection (LTBI) among HIV-negative individuals, and the annual risk and force of infection during childhood and adolescence.

DESIGN: A cross-sectional survey using a standardised tuberculin skin test (TST) in HIV-negative individuals aged 5–40 years. A TST diameter of ≥10 mm was defined as indicative of LTBI.

RESULTS: Among 1061 individuals, only 4.7% had low-grade TST responses of 1–9 mm. However, the proportions of individuals with TST ≥10 mm increased from 28.0% in the 5–10 year age stratum to 88.0% in the 31–35 year age stratum. The mean annual risk of infection was 3.9% up to 5 years of age. The estimated force of infection (the rate of acquisition of LTBI among the residual pool of non-infected individuals) increased throughout childhood to a maximum of 7.9% per year at age 15 years.

CONCLUSIONS: Extremely high rates of infection in childhood and adolescence result in very high LTBI prevalence rates in young adults who are most at risk of acquiring HIV infection. This may be an important factor fuelling the high rates of HIV-associated TB in southern Africa.

Keywords: Africa; TB infection; TST; age; sex

Document Type: Regular Paper

Affiliations: 1: Desmond Tutu HIV Centre, Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Cape Town, South Africa 2: Developmental Center for AIDS Research and Department of Biostatistics and Computational Biology, University of Rochester School of Medicine and Dentistry, New York, New York, USA 3: Institute of Infectious Diseases and Molecular Medicine, University of Cape Town, Cape Town, South Africa; and Division of Medicine, Imperial College, London, UK 4: Institute of Infectious Diseases and Molecular Medicine, University of Cape Town, Cape Town, South Africa 5: Institute of Infectious Diseases and Molecular Medicine, University of Cape Town, Cape Town, South Africa; Division of Medicine, Imperial College, London, UK; and National Institute for Medical Research, London, UK 6: Desmond Tutu HIV Centre, Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Cape Town, South Africa; and Department of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, UK

Publication date: April 1, 2010

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  • The International Journal of Tuberculosis and Lung Disease publishes articles on all aspects of lung health, including public health-related issues such as training programmes, cost-benefit analysis, legislation, epidemiology, intervention studies and health systems research. The IJTLD is dedicated to the continuing education of physicians and health personnel and the dissemination of information on tuberculosis and lung health world-wide.

    Certain IJTLD articles are selected for translation into French, Spanish, Chinese or Russian. They are available on the Union website

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