This study will assess the next generation of blood tests for latent TB infection, which may be able to indicate how treatment is working as well as in diagnosis infection.

Currently available blood tests for latent tuberculosis infection (LTBI) identify people who have been previously infected with M. tuberculosis. Whilst they are sensitive and specific, they cannot be used to monitor the effectiveness of treatment for LTBI. New blood tests ("fourth generation Quantiferon tests") give a more complete measurement of the workings of the immune system, which may be useful to show whether treatment is working. These new tests have not yet been evaluated in clinical practice, so their usefulness in identifying people at highest risk of TB disease and monitoring treatment is unknown.

Mass gatherings, such as the annual Hajj pilgrimage, may encourage the spread of infectious diseases, including respiratory infections such as influenza, respiratory syncytial virus, and possibly also tuberculosis. However, the risk of TB infection during the Hajj has not been reliably measured. It is important to measure this risk so that pilgrims can be given suitable advice about preventing infection.

Inclusion Criteria:

- Contacts: Adult (aged 16 years or older) contacts of smearpositive pulmonary TB patients attending participating TB clinics or primary care centres for screening will be invited to take part. Contacts will include all individuals with a cumulative duration of exposure of greater than eight hours to the relevant index case in a confined space during the period of infectiousness (prior to initiation of treatment). Patients with active TB: Newly diagnosed, microbiologically confirmed tuberculosis disease (pulmonary or extrapulmonary) attending participating TB clinics or primary care centres. Hajj pilgrims: Individuals arranging travel to Saudi Arabia for the Hajj through participating tour operators.

Exclusion Criteria:

- Contacts: Active TB disease. Individuals who are unable to give informed consent. Children aged under 16 years.

TB cases: Individuals who are unable to give informed consent. Children aged under 16 years.

Hajj pilgrims: Active TB disease. Any health indication which would prevent travel to Saudi Arabia. Individuals who are unable to give informed consent. Children aged under 16 years.