Epidemiology of tuberculosis in Europe.

The risk of exposure to tuberculosis depends upon the incidence of infectious cases, the duration of their infectiousness, and the number of personal interactions an infectious case accomplishes per unit of time. The risk of infection, given exposure, depends on the density of infectious particles in the ambient air x duration of exposure to that air. The risk of infection has rapidly declined in Europe for decades by 10% or more annually, resulting in a shift of the infected to the oldest generation. Thus, with the passage of time, cohorts are increasingly replaced by successive cohorts with less and less infection. The risk of progression from infection to tuberculosis depends largely on the cellular immune system's capability to prevent tubercle bacilli from multiplication. The three most important risk factors for the progression from subclinical infection to tuberculosis include: human immunodeficiency virus (HIV) infection, recency of infection, and fibrotic residuals from earlier tuberculosis. The number of tuberculosis cases has rapidly decreased during this century, accompanied by an upward shift in the median age of patients. In recent years, tuberculosis among immigrants has gained in significance and is likely to continue to do so, while HIV infection has limited impact on the tuberculosis epidemic in Europe. The risk of dying from tuberculosis is determined by form and site of disease, and patient's and doctor's delay. The number of deaths caused by tuberculosis in Europe is rapidly decreasing.