Human Immunodeficiency Virus (HIV) is the strongest individual risk factor for the reactivation of tuberculosis (TB) after previous exposure to Mycobacterium tuberculosis (MTb). This risk is reduced but not completely eliminated when HIV is treated with antiretroviral therapy (ART). Both the British HIV Association (BHIVA) and National Institute of Health and Care Excellence (NICE) suggest testing for latent TB infection in HIV infected individuals, but use different criteria. The cost -effectiveness of either approach has not been assessed, nor is testing widespread. A certain proportion of HIV infected subjects in Africa have MTb detectable in their sputum despite not having symptoms (such as cough or weight loss), nor changes on a chest x ray. It is unclear if this happens in lower TB prevalence areas such as the United Kingdom (UK). We intend to test a cohort of HIV infected subjects for evidence of latent TB using a tuberculin skin test (TST) and Interferon Gamma Release Assay (IGRA), ask about symptoms (using a standardised questionnaire) and to induce sputum using a saline nebuliser, to detect MTb using microscopy and culture, and newer nucleic acid amplification (genetic) techniques. Some patients, despite being exposed to TB in the past, will not mount a response using an IGRA or TST, which maybe due to an abnormal immune response. This lack of response seems more common in HIV. By investigating the number of patients with positive TST, IGRA, chest X ray and evidence of MTb in their sputum, in the context of place of birth, previous exposure to TB, CD4 count and other medications, we can assess the cost- effectiveness of systematic TB screening and the use anti-TB antibiotics to prevent reactivation of TB. In time, we will be able to answer important questions about the time taken to reactivate TB in individuals with HIV who do or don't take preventative anti-TB medications in the UK.