HIV increases the risk of tuberculosis (TB). But how does this risk change over time after HIV infection? Researchers from the London School of Hygiene and Tropical Medicine studied the effect of HIV on the risk of TB among 23,874 miners at four gold mines in Gauteng Province, South Africa.

South African gold miners have among the highest TB rates in the world. Understanding the impact of HIV on TB risk is important for modelling the two epidemics and for planning interventions, including the use of antiretroviral drugs. The mines provide a good opportunity to study this issue because they have:

• stable populations
• good medical records
• extensive infrastructure
• high quality health care services
• similar working and living conditions for HIV-positive and negative miners.

The study took place over seven years in four gold mines in Gauteng Province, South Africa. The miners are all men aged 18 to 65 years old.

The research showed that:

• At the start of the study, 3,371 miners were HIV-positive and another 2,737 became infected during the study. The remaining 17,766 were HIV-negative throughout.
• There were 740 cases of TB. The number of new TB cases increased with time after HIV infection, calendar year and age.
• There were 2.9 cases per 100 person-years (an estimate of the actual time at risk in years, months, or days that all persons contributed to a study) at risk in HIV-positive miners compared with 0.80 cases per 100 person-years at risk in HIV-negative miners.
• TB risk doubled within the first year of HIV infection with a further slight increase every year for seven years.

These results challenge current models, which usually assume that there is no increase in TB risk during the first few years after HIV infection. HIV probably increases the risk of primary disease after initial TB infection, as well as disease due to reactivation of dormant infection and disease due to reinfection with a new strain. It may also increase the risk of picking up TB infection in the first place.

Antiretroviral drugs reduce TB rates but are not often used at early stages of HIV infection. So other strategies are needed to curb this early increased risk. As well as tackling the infection directly, these should target the causes of high TB rates, such as silicosis (from inhalation of silica dust), crowded living conditions and high risk of HIV infection. At the mines, innovative strategies such as mass TB preventative treatment with isoniazid may be suitable because even HIV-negative miners have a high risk of TB.

Source(s):
‘How soon after infection with HIV does the risk of tuberculosis start to increase? A retrospective cohort study in South African gold miners’, The Journal of Infectious Diseases 191, pages 150-158, by Pam Sonnenberg, et al., 2005 Full document.

Funded by: Colt Foundation, Overseas Research Students Award Scheme, UK Department for International Development

id21 Research Highlight: 19 May 2006

Further Information:
Pam Sonnenberg
Communicable Disease Surveillance Centre
61 Colindale Avenue
London NW9 5EQ
UK

Contact the contributor: pam.sonnenberg@lshtm.ac.uk

London School of Hygiene and Tropical Medicine, UK

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'No change: spread of TB constant despite raging HIV epidemic'

'Battling the bugs - cutting death rates among HIV-positive TB patients'

'Charity begins at home - community care for HIV and TB patients in Zambia'

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