TUBERCULOSIS: Children are different

Disease risk after primary infection with Mycobacterium tuberculosis is greatest in infants (younger than 4 years), and declines slowly to a nadir at age 5—10 years.6 During adolescence (age 15—19 years), there is a rapid increase in risk with a second peak between the ages of 20—30 years.6 Age-related differences in disease risk are accompanied by differences in the response to infection and clinical features of disease. In early childhood, disseminated forms of disease, such as miliary tuberculosis and tuberculous meningitis, are common, and exuberant hilar lymph-node responses contribute to airway pathology.4, 6 With increasing age, these features become less common, with a sudden shift in pathology noted during adolescence.4, 6 Tuberculosis at this stage shows features of so-called adult-type disease (previously called post-primary tuberculosis), the hallmark of which is tissue destruction and lung cavitation.4, 6
Understanding the mechanisms that cause this sudden transition are fundamentally important4, 7 because lung cavitation promotes disease transmission and ongoing transmission sustains the epidemic—the primary evolutionary bottleneck that must be overcome for the pathogen to thrive in a human population. Little is known about either bacterial or host features that allow transmission. A prominent sex-related difference is the early predominance of adult-type cavitary lung disease in women, which can persist until age 35 years. The age of transition to predominance varies, but tends to become earlier as the incidence of tuberculosis declines.2, 3, 8
http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(10)60580-6/fulltext