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Vaccinations with live virus vaccines (for example the MMR vaccine against measles, mumps, and rubella) or virus infections, such as measles, HIV or influenza, can temporarily decrease the tuberculin reaction. Other diseases including cancer and sarcoidosis, can lower sensitivity to tuberculin. Persons who are undernourished and those undergoing immunosuppressive treatment (i.e. Corticosteroids) may suppress the reactivity to the tuberculin test.
A person with active tuberculosis may demonstrate a reaction of less than 6 mm if the immune system is severely depressed by the tuberculosis infection.
An individual may demonstrate a positive Mantoux test although no infection with tuberculosis is/was present. This may be due either to a previous BCG vaccination, or to an earlier infection with an environmental non-tuberculous mycobacterium which did not cause overt disease.
