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The Mantoux test

Scenario: Reg is 55 and shares a house with other men. His health seems to be declining rapidly lately. He is always tired, coughs loudly and incessantly, is losing weight, and sweats during his broken sleep. A doctor soon diagnoses active tuberculosis (TB). You and Reg's flatmates are then advised to have a Mantoux screening test. Your are told it is a small painless injection of dead TB germs under the skin, with the aim of eliciting a skin reaction some three to five days later. You are concerned about the test. Why have it? What will it show? Will you be quarantined?

The Mantoux test will show either:

1. No reaction to TB ('Mantoux negative'). In other words, there is no infection or exposure to TB. or
2. A positive reaction ('Mantoux positive') with swelling in the skin. Note that a positive reaction is not necessarily bad news. It suggests either past or present exposure to TB, or past BCG vaccination. Further tests are needed.

BCG vaccination against TB gives reasonable but not total immunity. The main disadvantage of BCG is that it renders subsequent Mantoux tests more difficult to interpret, and the decision to have this vaccination should be made in consultation with your doctor. BCG should not be given where HIV infection is present or where pregnancy cannot be ruled out.

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