is nine months of isoniazid, but this regimen is not widely used outside of the US. Terminology There is no agreement regarding terminology: the terms preventive therapy and chemoprophylaxis have been used for decades, and are preferred in the UK because it involves giving medication to people who have no disease and are currently well: the reason for giving medication is primarily to prevent people from becoming unwell. In the U.S., physicians talk about latent tuberculosis treatment because the medication does not actually prevent infection: the person is already infected and the medication is intended to prevent existing silent infection from becoming active disease. There are no convincing reasons to prefer one term over the other. Specific situations "Populations at increased risk of progressing to active infection once exposed: Persons with recent TB infection [those infected within the previous two years] Congenital or acquired immunosuppressed patients (in particular, HIV-positive patients) Illicit intravenous drug users; alcohol and other chronic substance users Children (particularly those younger than 4 years old) Persons with comorbid conditions (ie, chronic kidney failure, diabetes, malignancy, hematologic cancers, body weight of at least 10% less than ideal, silicosis, gastrectomy, jejunoileal bypass, asthma, or other disorders requiring long-term use of corticosteroids or other immunosuppressants)." Treatment regimens It is essential that assessment to rule out active TB be carried out before treatment for LTBI is started. To give treatment for latent tuberculosis to someone with active tuberculosis is a serious error: the tuberculosis will not be adequately treated and there is a serious risk of developing drug-resistant strains of TB. There are several treatment regimens currently in use: 9H — isoniazid for 9 months is the gold standard (93% effective, in patients with positive test results and fibrotic pulmonary lesions compatible with tuberculosis). 6H — Isoniazid for 6 months might be adopted by a local TB program based on cost-effectiveness and patient compliance. This is the regimen currently recommended in the UK for routine use. The U.S. guidance excludes this regimen from use in children or persons with radiographic evidence of prior tuberculosis (old fibrotic lesions) (69% effective). 6 to 9H2 — An intermittent twice-weekly regimen for the above two treatment regimens is an alternative if administered under Directly observed therapy (DOT). 4R — rifampicin for 4 months is an alternative for those who are unable to take isoniazid or who have had known exposure to isoniazid-resistant TB. 3HR —