Slide 040 Epidemiologic Basis of Tuberculosis Control
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The impact of the prevalence of tuberculous infection on the predictive value of a positive tuberculin skin test is exemplified in this model applied to findings in the US Navy recruit study.

Navy recruits who have a history of contact with a tuberculosis case are expected to have a higher prevalence of infection than those without such a history.

Among persons without a known history of contact only about 10% with an induration of 10 mm will actually have tuberculous infection.  Among recruits with a history of contact, the expected prevalence of tuberculous infection is much larger.  With the same induration of 10 mm, the test is now correct in about 80%.

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Last update: September 10, 2010