13.4.3 What is the difference between TB infection and TB disease?
As you’ve just learnt, in a TB infection, an individual has no signs and symptoms of TB disease, whereas in pulmonary TB disease, signs and symptoms are evident. There are other differences between TB infections and pulmonary TB disease and these are summarised in Table 13.1.
| Descriptions | TB infection | TB disease (in the lungs) |
|---|---|---|
| M. tuberculosis in the body | Yes | Yes |
| Symptoms | No | Yes |
| Chest X-ray | Normal | Abnormal |
| Sputum smears | Negative | Usually positive |
| Culture* | Negative | Positive |
| Infectious to others? | No | Yes |
| A case of TB | No | Yes |
*TB bacteria isolated from the patient are grown in a culture medium in the laboratory, so they can be identified.
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13.4.2 Natural history of tuberculosis