1. Presentation 10 Analysing results and defining cases

2. Sputum smear microscopy: Sputum should be examined in ALL suspected cases.
M. tuberculosis is identified microscopically by its staining characteristics: it has a thick fatty cell wall which cannot be penetrated by stains most commonly used in smear microscopy when investigating chest infections, which is why it is classified as an “acid-fast bacillus” (AFB).
It is essential to identify TB suspects promptly so that the correct tests can be ordered and carried out as soon as possible.
The most common stain used in the detection of AFB is the Ziehl-Neelsen stain. AFB are stained bright red and stands out against a blue background. In addition, AFB can be visualised by fluorescent microscopy when using an auramine-rhodamine stain.

3. Patients with pulmonary TB are referred to as either smear positive or smear negative:
Pulmonary TB; sputum smear positive (PTB+):
Is the most infectious form of TB
Refers to patients who have enough TB bacilli (AFB) in their sputum that they can be identified under a microscope when a Ziehl Neelsen or auramine stain (AFB Smear) is used:
at least two initial sputum smear examinations need to be positive for AFB;
or: one sputum specimen AFB+ and radiographic abnormalities consistent with active pulmonary TB;
or: one sputum specimen AFB+ culture positive for TB bacilli.

4. Pulmonary TB; sputum smear negative (PTB-):
If a patient has symptoms suggestive of TB, at least 3 sputum examinations negative for AFB, and radiographic abnormalities consistent with active pulmonary TB, the patient should receive a full course of anti-TB therapy.
Smear positive patients tend to have a more advanced stage of the disease; more lung damage and so cough up more infectious material. Thus, they are usually more contagious. Knowing whether the patient is smear negative or smear positive is important for two reasons:
Sputum conversion from smear positive to smear negative or vice versa is one of the indicators of a patient’s progress.
The status of the sputum smear can determine how to allocate scarce resources. In such situations smear positive patients take priority in treatment over less infectious smear negative cases.

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