Much more informative than a point estimate of the risk of infection is the secular trend in the annual risk of infection.  If serial tuberculin surveys are available, then such trends can be calculated.

The risk of infection was very large in Europe 100 years ago, it was in the order of magnitude of 10%.  It declined rapidly.  The average annual decline may have been around 5% before the introduction of chemotherapy and 10% and more thereafter.

It may be noted that for instance the epidemiology of tuberculous infection in France from these estimates lags about 15 years behind the Netherlands.  Over the time frame relevant in tuberculosis epidemiology this is, however, not of much importance.  If the trend has continued, France is now at similarly or even lower level than the Netherlands in 1980.  The slope parameter of decline is of more importance than the intercept parameter over a sufficiently long period of time.

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