HomeDetails of the pathogenesis of TB are outlined in Chapter 2: Transmission and Pathogenesis of Tuberculosis. Children inhale Mycobacterium tuberculosis (M. tuberculosis) from adults or adolescents with infectious pulmonary or laryngeal TB that has been aerosolized. Rarely, children have cough or multibacillary disease, and are infectious.7,8 Primary infection generally consists of a parenchymal focus with regional intrathoracic lymph node enlargement. The parenchymal lesion may enlarge and caseate or nodes may enlarge and compress or erode through a bronchus, causing wheezing, segmental pneumonia or atelectasis. The primary infection is usually accompanied by an occult, subclinical bacteremia that seeds distant sites. This may rapidly lead to severe forms of disease, including miliary and central nervous system (CNS) TB. In general, the risk of progression to TB disease and of severe forms of TB disease after infection is highest in children younger than 5 years old (Table 2).6 However, in most cases, the primary focus heals and the bacteria may survive in a state of immune containment that is referred to as TB infection.
Table 2. Average age-specific risk for disease development after untreated primary infection.
| Age at primary infection | Manifestations of disease | Risk of disease (%) |
|---|---|---|
| <12 months | No disease | 50 |
| Pulmonary disease | 30-40 | |
| TB meningitis or miliary disease | 10-20 | |
| 12-23 months | No disease | 70-80 |
| Pulmonary disease | 10-20 | |
| TB meningitis or miliary disease | 2-5 | |
| 2-4 years | No disease | 95 |
| Pulmonary disease | 5 | |
| TB meningitis or miliary disease | 0.5 | |
| 5-10 years | No disease | 98 |
| Pulmonary disease | 2 | |
| TB meningitis or miliary disease | <0.5 | |
| >10 years | No disease | 80-90 |
| Pulmonary disease | 10-20 | |
| TB meningitis or miliary disease | <0.5 |
Source: Adapted from Marais et al. 9
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