HomeIn Canada, most TB is understood to be “reactivation” TB (ie, occurring in adolescents or adults). It usually presents as adult-type pulmonary disease (upper lung-zone fibrocavitary disease — previously referred to as postprimary TB — beginning in small foci that are the result of remote lympho-hematogenous spread), although it may also present as extrapulmonary TB. As mentioned earlier, adult-type pulmonary TB may on occasion be a manifestation of primary TB or a reinfection. In any population group, reactivation of TBI, leading to reactivation TB, is much more likely to occur in people who are immunocompromised.
Patients with adult-type pulmonary TB are much more likely to show lung cavitation (created when caseous material liquefies) that erodes into the bronchi.88 Within the unique extracellular environment of cavities, host defenses are ineffectual, and bacteria multiply in large numbers. Because cavities are open to, and discharge their contents into, nearby bronchi, these same bacteria are directly communicable to the outside air when the patient coughs.89 From the perspective of public health and the organism’s ability to survive as a species, adult-type pulmonary TB is the most important form of TB disease.
Persons with a history of untreated or inadequately treated pulmonary TB or a “high-risk” lung scar (upper lung-zone fibronodular abnormality) on chest radiograph are thought to have a higher bacillary burden, even though “dormant,” than those without such a history/radiograph and to be at increased risk of reactivation TB.90,91 This scenario is commonly seen among immigrants referred to public health authorities for medical surveillance.
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