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The number of new cases of a disease in a population over a period of time: normally expressed as number of cases per 100,000 population annually.

Immune system

The body’s defence system against outside attackers. The immune system fights off infection and retains memory cells that will protect against future attack.

Incubation period

The interval between infection and the development of clinically evident disease.

Influenza-like syndrome

A side effect of rifampicin. Paradoxically, it is more common when rifampicin is given twice or three times a week than when given daily.

Initial drug resistance

See primary drug resistance.
Intensified case finding

Strategies to identify and treat people with TB who do not present to healthcare facilities on their own initiative. This includes: regular screening of all people with HIV or at high risk of HIV; screening of people living and working in congregate settings – where TB is more likely to spread – such as mines or prisons; screening household contacts of people already diagnosed with TB.


Literally ‘between white cells’, these are cytokines that have been well characterised and allocated numbers. Many are involved in immune responses in tuberculosis.


A synthetic agent and one of the first line anti-tuberculosis drugs. It is particularly effective against actively replicating bacilli in the lung cavities. It is also used for preventive therapy in those with latent tuberculosis.

Isoniazid preventive therapy (IPT)

Isoniazid preventive therapy can be used alongside antiretrovirals to further reduce the risk of TB in HIV-infected persons. PLHIV should be screened for active TB and started on either TB treatment or isoniazid preventative therapy as appropriate.

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