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See separate related articles Tuberculosis and BCG vaccination.
Preventing transmission of tuberculosis (TB), contact tracing, screening and bacillus Calmette-Gueérin (BCG) vaccination are key targets in tuberculosis prevention. Although the routine BCG vaccination of all children was discontinued in the UK in 2005, it has been replaced by a TB risk-based programme. It targets contacts of any known TB cases and those children at most risk of exposure to TB, particularly from the more serious childhood forms of the disease.
Whom to screen
Screening and testing of high-risk and contact groups are designed to identify new cases (eg healthcare workers, new immigrants and HIV patients). New immigrants to the UK should be identified for TB screening from the following information: 
- Port of arrival reports.
- New registrations with primary care.
- Entry to education (including universities).
- Links with statutory and voluntary groups working with new entrants.
Neonatal BCG vaccination for any baby at increased risk of TB should be discussed with the parents or legal guardian. Primary care organisations with a high incidence of TB should consider vaccinating all neonates soon after birth. 
Which test to use
Screening is done using either a Mantoux (skin) test or interferon-gamma (blood) test (IGT).
- Household or other close contacts (e.g in workplaces and schools).
- Aged 2-5 years: offer Mantoux test and, if positive, refer to a TB specialist for exclusion of active TB and possible treatment of latent TB. If Mantoux test is negative (but the child is a contact of sputum-smear-positive disease), offer IGT after 6 weeks and repeat the Mantoux test to increase the sensitivity (to reduce false negative results).
- Aged ≥5 years: offer Mantoux test and consider IGT if Mantoux positive results, or where Mantoux testing may be less reliable, for example BCG-vaccinated people. If Mantoux testing is inconclusive, refer the person to a TB specialist.
- Children aged under 2 years require anti-TB treatment - see the National Institute for Health and Clinical Excellence (NICE) guidance.
- New entrants from high-incidence countries:
- Aged under 5 years: offer Mantoux test and, if positive, refer to a TB specialist for exclusion of active TB and possible treatment of latent TB.
- Aged 5-15 years: offer Mantoux test; follow with IGT if positive.
- Aged 16-35: offer IGT alone or (dual strategy, i.e following Mantoux test).
- If aged 35 years, consider the individual risks and benefits of likely subsequent treatment, before offering testing.
- Children: refer to a specialist if infection is suspected.
- Adults: perform IGT ± Mantoux and, if either is positive, assess for active disease and consider treatment for latent infection. For people with HIV and CD4 counts less than 200 cells/mm3 performing both Mantoux testing and IGT is recommended.
- Healthcare workers:
- Those who have not had a BCG vaccination: screen with Mantoux test and vaccinate with BCG if negative.
- NHS employees who have recently arrived from high-incidence countries or who have had contact with patients in settings where TB is highly prevalent: offer IGT.
- Hard to reach groups: - offer a single IGT.
Skin testing can detect previous exposure to the organism (or BCG vaccination) by provocation of a well established, cell-mediated immune reaction. A purified protein derivative (PPD) of Mycobacterium tuberculosis is injected intradermally into the flexor surface of the forearm and the local response is measured. The interpretation of tuberculin tests depends on BCG vaccination history, immune status and concurrent viral infection. For example, in HIV-positive patients, a negative tuberculin test does not exclude TB as it may be due to general anergy.
The standard skin test for TB in the UK is the Mantoux test. The Mantoux test is used (2 different strengths) both:
- As a screening test for TB infection or disease (2 TU/0.1 ml).
- As an aid to the clinical diagnosis of TB infection (10 TU/0.1 ml).
The local skin reaction to tuberculin PPD injected into the skin is used to assess an individual's sensitivity to tuberculin protein. The greater the reaction, the more likely it is that an individual is infected or has active TB disease. Precise interpretation depends on whether it is being used for screening or clinical diagnostic purposes.
|Mantoux - Tuberculin Skin Testing in Screening|
|Diameter of induration||Positivity (degree of hypersensitivity to tuberculin protein).||Interpretation|
|Less than 6 mm||Negative - (no significant hypersensitivity to tuberculin protein).||
|6 mm or greater, but less than 15 mm||Positive - (hypersensitive to tuberculin protein).||
|15 mm and above||Strongly positive - (strongly hypersensitive to tuberculin protein).||
- How to administer:
- Mantoux test (0.1 ml, 27-gauge needle, raise 6-10 mm wheal).
- Read at 48 to 72 hours.
- The tine test and Heaf's test are no longer recommended (lack of sensitivity and specificity).
- Care and consultation are needed in interpretation, especially when used in clinical diagnosis. For example:
- Positive at >5 mm in contacts, immunosuppressed, abnormal CXR.
- Positive at >10 mm in at-risk and under five years.
- Positive at 15 mm or more in over age five and without risk factors.
- Beware false positives and false negatives.
- Previous BCG may affect interpretation (IGT is better in these circumstances).
Heaf's test is no longer recommended in the UK where it was used for larger less targeted screening programmes (it used a 6-pointed apparatus to deliver the solution, and the degree of induration at the puncture site was measured 3-10 days later).
This should be carried out by the multidisciplinary TB team. Detailed guidance has been outlined by NICE.
- It aims to detect people infected with TB but with no clinical evidence of disease (10% of all TB diagnoses).
- It aims to identify BCG vaccination candidates.
- Detect a source patient, eg when a child is diagnosed with TB.
Screening is recommended for selected contacts, since the source case has exhibited respiratory symptoms. If this is unknown, contacts during the 3 months preceding the initial diagnosis are screened. Tracing should be extended backwards if necessary.
- Initially, screen people from the same household and any frequent visitors of the index case. If the index case has pulmonary TB, all close contacts should be screened. Screening is not usually necessary for contacts of non-pulmonary TB patients.
- Screening of casual contacts is less fruitful and is only necessary if the index case is highly infectious or the contacts are particularly susceptible, such as young children or immunocompromised adults. Casual contacts include occupational contacts or healthcare workers.
Contacts are assessed, as per British Thoracic Society guidelines, with regard to:
- BCG vaccination status
- Screening test - Mantoux test or IGT (see above).
- CXR findings.
Management of contacts
Treatment should be considered if a contact has evidence of:
- Tuberculous disease, ie positive skin test with clinical signs and symptoms. Begin one of the standard treatment regimens.
- Latent tuberculous infection, ie positive skin test but asymptomatic and normal CXR, suggesting presence of small numbers of bacteria in the body, which may later cause disease.
See separate Tuberculosis article for treatment of latent infection
- BCG vaccination is recommended for uninfected contacts who fulfil all of the following criteria:
- Child under 16 years of age.
- Previously unvaccinated.
- Persistently tuberculin negative.
Further reading & references
- Immunisation - The Green Book; Dept of Health
- Tuberculosis, NICE Clinical Guideline (March 2011)
- Stopping Tuberculosis in England: An action plan from the Chief Medical Officer, Dept of Health, 2004
- BTS Guidelines; Control and prevention of tuberculosis in the United Kingdom: Code of Practice 2000. Joint Tuberculosis Committee of the British Thoracic Society. Thorax 2000;55:887-901.
Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.
|Original Author: Dr Richard Draper||Current Version: Dr Huw Thomas||Peer Reviewer: Dr Hayley Willacy|
|Last Checked: 28/09/2011||Document ID: 2891 Version: 26||© EMIS|