Tuberculosis

One of the major diseases in the world, tuberculosis poses considerable challenge in developing countries. Not only are a proportion of the population infected with this debilitating and often fatal disease, but the period of infectiousness is prolonged (approximately 5 years in an untreated case), permitting transmission to many other persons. Indeed, in a number of countries, an endemic balance has been achieved whereby the number of cases that resolve spontaneously, are cured by medical treatment or die, are replaced by an equal number of new cases entering the pool of tuberculosis. HIV infection has added to the likelihood of people developing tuberculosis so that it is increasing in sub-Saharan Africa. In the world, 8 million people develop tuberculosis every year and 2 million die from it.

Organism Mycobacterium tuberculosis, but infection can also be caused by M. bovis (from cattle) or M. africanum. There are many mycobacteria occurring naturally, including M. avium, M. intracellulare and M. scrofulaceum, that can sensitize the individual and interfere with BCG vaccination. In endemic countries, M. tuberculosis is widespread, with 1-3% of the population per year being at risk of infection.

Clinical features A productive cough with weight loss, fever and anaemia are the most important signs of tuberculosis. Any chronic cough persisting for 3 weeks or more, especially if there is also weight loss and anaemia, should be regarded as a possible case of tuberculosis and sputum smears taken. Haemoptysis is an important diagnostic sign and may be streaking of the sputum with blood or frank coughing-up of fresh blood.

Tuberculosis infects people in a spectrum of severity depending on the host response, the dose of organisms and the length of time. The first sign of infection is the primary complex in which the organism is localized to an area of the lung with a corresponding enlargement of the hilar lymph nodes. In the majority of people, this heals completely or with a residual scar, and the person develops immunity to further challenge. If healing does not occur, then the focus extends to cause glandular enlarge ment, pleural effusion or cavity formation. The third phase of the disease results from complications of the regional nodes. These may be obstructive, leading to collapse and consolidation, cause erosion and bronchial destruction or spread locally. The final stage is one of blood stream spread, disseminating bacilli to all parts of the body where they may produce tuberculous meningitis or mil-iary infection. Long-term complications are those of bones, joints, renal tract, skin and many other rare sites. These features are illustrated in Fig. 13.1.

The risk of developing local and disseminated lesions decreases over a period of 2 years. If the majority of cases are going to progress, they will do so within 12 months of infection or 6 months from the development of the primary complex. By the end of 2 years, 90% of the complications would have occurred. Bone and other late complications are a very small proportion beyond this time.

Diagnosis Tuberculosis is spread by droplet infection, so sputum-positive cases transmit the disease much more efficiently than those whose sputum is negative on microscopy. The risk to the community is, therefore, from pulmonary tuberculosis and the emphasis should be on finding these cases by taking a sputum smear, ideally confirmed by culture. The comparative costs of diagnostic techniques are:

Smear

0.02

Culture

0.20

Sensitivity

0.40

Full plate X-ray

1.00

Fifty sputum smears can be made for the equivalent cost of one X-ray and this economy can be used for diagnosing cases in the community. Anybody presenting to the health services with a cough for 3 weeks or more should be asked to produce some sputum and a smear made. This is dried and stained with Ziehl-Neelsen for acid-fast bacilli. X-ray examination has a high sensitivity and, therefore, is of more value in countries with a low incidence and plentiful

Infection

Primary complex

(majority of cases heal)

Extension of the focus Pleural effusion or cavitation

(25% of cases occur within 9 months, 75% within 12)

Fever of onset

Bloodstream dissemination Meningitis or miliary

Complications of regional nodes

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