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.

Table 13.1  The distinction between TB infection and pulmonary TB disease.

DescriptionsTB infectionTB disease (in the lungs)
M. tuberculosis in the bodyYesYes
Symptoms NoYes
Chest X-ray NormalAbnormal
Sputum smears NegativeUsually positive
Culture*NegativePositive
Infectious to others?NoYes
A case of TB NoYes

*TB bacteria isolated from the patient are grown in a culture medium in the laboratory, so they can be identified.

13.4.2  Natural history of tuberculosis

13.5  Case finding