It is essential to identify and treat contacts of
tuberculosis patients with active disease. Persons exposed through close, prolonged or frequent contact may develop
tuberculosis, usually within two years following exposure. What is the harm-benefit balance of
tuberculosis prophylaxis in contacts at risk? To answer this question, we conducted a review of the literature, using the standard Prescrire methodology. Standard prophylaxis for
pulmonary tuberculosis consists of
isoniazid monotherapy for 6 to 12 months.This regimen has been tested in randomised placebo-controlled trials involving
tens of thousands of persons with a positive
tuberculin skin test (TST).
Pulmonary tuberculosis occurred in 0.6% of patients in the
isoniazid groups versus 1.7% in the placebo groups, after a follow-up of at least 2 years. However,
isoniazid can cause severe hepatic disorders and numerous drug interactions.
Rifampicin monotherapy was shown to be effective in only one placebo-controlled trial in patients with
silicosis, who have a very high risk of developing
tuberculosis.
Rifampicin also carries a high risk of drug interactions but is less hepatotoxic than
isoniazid. A 3-month course of the isoniazid+
rifampicin combination had a similar harm-benefit balance as a 6- or 9-month course of
isoniazid monotherapy. The
rifampicin +
pyrazinamide combination is no more effective than
isoniazid monotherapy but has more hepatic adverse effects. British guidelines issued in 2011 recommend treatment for contacts who have signs of
latent tuberculosis infection, based mainly on a positive TST or
gamma interferon release assay, and are at high risk of developing active
tuberculosis. patients aged at least 2 years who are strongly suspected of having
latent tuberculosis infection: either
tuberculosis treatment, or chest radiography 3 and 12 months after initial diagnosis. In practice, contacts of infectious patients have a low risk of developing clinical
tuberculosis.Treatment reduces the risk of
tuberculosis but exposes a large number of persons to numerous, sometimes serious, adverse effects. Watchful waiting for 2 years, without treatment, is often the best option.