Final answer:
Reactivation TB occurs when dormant TB bacteria within Gohn complexes are released, usually due to immunocompromise, leading to clinical symptoms like a chronic, bloody cough.
Step-by-step explanation:
Reactivation TB, also known as secondary TB, most commonly occurs in people who are immunocompromised, such as those with alcoholism, the elderly, or in those with other conditions that weaken the immune system. After the initial TB infection is contained, viable bacteria remain dormant within calcified lesions known as Gohn complexes, visible on chest radiographs.
When these dormant bacteria are released, due to a weakening of the immune system, they can cause a reactivation of the disease, characterized by symptoms such as a chronic, bloody cough. The Mantoux tuberculin skin test is used to detect exposure to TB, but a chest radiograph is necessary to confirm the presence of Gohn complexes and to differentiate a true infection from a false-positive result due to prior BCG vaccinations.