The age-specifc prevalence of tuberculous infection may also vary over time, as this example from Switzerland shows.

In the 1920ies, the chance of escaping infection by the time of reaching adulthood was virtually nil.  Thirty years later, the chances had increased to 50%, and 60 years later to almost 90%.  By 1990, the prevalence of tuberculous infection in young adults had become un-measurable.

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