Guidelines on the Prevention and Control of Tuberculosis in Ireland

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<strong>Guidelines</strong> on the Prevention and Control of Tuberculosis in Ireland 2010HSE/HPSC2. Methods of Tuberculosis ScreeningDiagnosis of active or latent TB involves a number of tests. There is no gold standard for determiningwhether a person is infected with M. tuberculosis but in practice the tuberculin skin test (TST) is thestandard method used. Recently immunological blood tests i.e. interferon-gamma release assays (IGRA)have been developed to aid diagnosis. However, neither the TST nor IGRA can be used to distinguishlatent infection from active disease.2.1 Definition of Active TBActive TB is defined as infection with mycobacteria of the M. tuberculosis complex, where mycobacteriaare growing and causing symptoms and signs of disease. This is distinct from LTBI where mycobacteriaare present but are inactive and not causing symptoms of disease. The diagnosis of active TB is mademost often on the basis of positive bacteriology but in approximately 15%-25% of cases on the basis ofappropriate clinical and/or radiological and/or pathological presentation as well as treatment response (seechapters 4 and 5).2.2 Definition of Latent TB InfectionA person with LTBI usually has a positive TST or IGRA test but has no physical findings of TB disease andthe chest X-ray is normal or only reveals evidence of healed infection i.e. granulomas or calcification in thelung, hilar lymph nodes or both. Persons with LTBI are asymptomatic and are not infectious (see table 3.1,chapter 3).The three screening methods discussed in this chapter are:1. Tuberculin skin test2. Interferon-Gamma Release Assays (IGRA)3. Chest X-ray.2.3 Tuberculin Skin TestThe main tool to diagnose TB infection is the TST. It is also used as an aid to the diagnosis of active TBdisease. In Ireland, the Mantoux test is the TST used. This test consists of the intradermal injection of asmall amount of purified protein derived from Mycobacterium tuberculosis bacteria (PPD). The local skinreaction to PPD is used to assess an individual’s sensitivity to the tuberculin protein. In a person who hascell-mediated immunity to these tuberculin antigens, a cell-mediated delayed hypersensitivity reaction willoccur within 48 to 72 hours. The reaction will cause localised swelling and will be manifest as induration ofthe skin at the injection site. The greater the reaction, the more likely it is that an individual is infected orhas active TB disease. In persons who are newly exposed and become infected with TB, this cell-mediatedreaction to tuberculin will develop 3 to 8 weeks later. 28WHO recommends that the Mantoux 2TU/0.1ml tuberculin PPD should be used and this is the standardtest recommended for use in Ireland. A comparative study undertaken by Comstock et al revealed that2TU has almost identical sensitivity to the use of 5TU for tuberculin testing although specificity was slightlylower with 2TU. 29 However, it was concluded that the results of testing with 2TU and 5TU were sufficientlysimilar to deem them biologically equivalent. 29Recommendation:The standard tuberculin skin test (TST) recommended for use in Ireland is the Mantoux2TU/0.1ml tuberculin PPD. Mantoux 10TU/0.1ml tuberculin PPD is not recommended for usein Ireland.In general testing for LTBI is indicated when the risk of development of disease is increased if the patient isinfected.-11-
<strong>Guidelines</strong> on the Prevention and Control of Tuberculosis in Ireland 2010HSE/HPSCThere are three general situations when the disease risk is increased:• Recent infection: most commonly contacts of a patient with a recent diagnosis of infectious TBdisease or immigrants or persons from countries of high TB incidence (≥40 per 100,000 TB casesnotified per year) within 2 years of arrival in Ireland• Increased risk of reactivation due to impaired immunity: This includes HIV infection andimmunosuppressed conditions e.g. diabetes, renal failure, immunosuppressant medications andpulmonary silicosis• When there is radiological evidence of old, healed inactive TB but no prior treatment. 30The following persons should not receive a TST:• Those who had severe blistering TST reactions in the past or with extensive burns or eczemapresent over TST testing sites, because of the greater likelihood of adverse or severe reactions• Those with documented active TB disease or a well-documented history of adequate treatment forTB infection or disease in the past. In such patients the test is of no clinical utility.• Those with major viral infections e.g. varicella (chickenpox), measles, mumps, infectiousmononucleosis BUT not the common cold or minor viral infections• Those who received MMR vaccines in the previous four weeks as this has been shown to increasethe likelihood of false negative TST results. No data are available in relation to the effect of otherlive virus vaccines e.g. varicella or yellow fever but it would be prudent to follow the same fourweek guidance. 30The following persons can receive a TST:• Those with a common cold• Those who are pregnant or breastfeeding• Those immunised with any vaccine on the same day• Those immunised within the previous 4 weeks with inactivated vaccines• Those who give a history of a positive TST reaction (other than blistering) that is not documented• Those taking low doses of systemic corticosteroids, < 15mg prednisolone (or equivalent) daily. Itgenerally takes a steroid dose equivalent to ≥15mg prednisolone daily for 2-4 weeks to suppresstuberculin reactivity. 30;31Administration of the Mantoux testIn all cases, the Mantoux test should be administered intradermally. This is also sometimes referredto as intracutaneous administration. The Mantoux test is normally performed on the flexor surface ofthe left forearm at the junction of the upper third and the lower two-thirds. If the skin is visibly dirty, itshould be washed with soap and water. The Mantoux test is performed using a 0.1ml tuberculin syringeor alternatively a 1ml graduated syringe fitted with a short bevel 26G (0.45x10mm) needle. A separatesyringe and needle must be used for each subject to prevent cross-infection. Then 0.1ml of PPD should bedrawn into the tuberculin syringe and the 25G or 26G short-bevelled needle attached to give the injection.The needle should be firmly attached and the intradermal injection administered with the bevel facinguppermost.The operator stretches the skin between the thumb and forefinger of one hand and with the other handslowly inserts the needle with the bevel upwards for about 5mm into the superficial layers of the dermisalmost parallel to the surface. The needle can usually be seen through the epidermis. A correctly givenintradermal injection results in a tense blanched raised bleb and considerable resistance is felt when thefluid is being injected. A bleb is typically of 7mm diameter following a 0.1ml intradermal injection. If littleresistance is felt when injecting and a diffuse swelling occurs rather than a tense bleb the needle is toodeep and should be withdrawn and reinserted intradermally on the opposite forearm or on the sameforearm at a site at least 10cm away from the previous injection. Do not cover the site with a bandage.Inform the patient that he or she should not scratch the site but may perform all normal activitiesincluding showering or bathing. Record the following details: a) date of injection; b) dose (2TU, 0.1ml);c) manufacturer; d) lot number; e) expiry date; f) site of injection and g) person who administered theinjection.-12-
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Guidelines on the Prevention and Control of Tuberculosis in Ireland

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