Home- With few exceptions, infection with Mycobacterium tuberculosis (M. tuberculosis) is acquired by inhalation of small droplet nuclei (1-5 microns in diameter) that contain just a few mycobacteria and that are capable of reaching the alveoli.
- The probability of transmission increases with the following:
- Bacterial burden (smear positivity) in the source patient
- Cavitary or upper lung-zone disease on chest radiograph in the source patient
- Laryngeal disease in the source patient
- Amount and severity of cough in the source patient
- Duration of exposure of the contact
- Proximity of the contact to the source patient
- Crowding and poor room ventilation
- Delays in diagnosis and/or effective treatment of the source patient
- The most effective way to reduce transmission is to promptly diagnose and treat patients with active pulmonary tuberculosis (TB).
- Through innate immune mechanisms, alveolar macrophages eradicate the bacteria in some individuals; in others, the bacteria are able to replicate and establish TB infection. Bacterial factors and host genetic factors that promote or limit acquisition of infection are not well understood.
- Between TB infection and active symptomatic pulmonary tuberculosis are 2 recently described intermediate states: incipient TB, a state that is likely to progress to active disease but does not cause detectable abnormalities; and subclinical TB, a state of disease due to viable M. tuberculosis that does not cause clinical TB-related symptoms, but does cause other abnormalities that can be detected using existing radiologic or microbiologic assays.
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