1. EPIDEMIOLOGY AND RISK FACTORS
Some 200 years ago, tuberculosis was a western-European export to the rest of the world. In the mid-1980s it was realised that the disease was out of control across most of the poorest regions of the world. In 1993 the WHO declared TB to be a world emergency.
Despite increasing intervention, cases are set to increase globally for the foreseeable future. Every two hours, as many people die from TB as have ever died from SARS.
One third of the world's population, two billion people, are infected with the tubercle bacillus. It is estimated that deaths from TB will increase from the present level of two million a year to five million by the year 2050.
In the UK, cases have been increasing since 1987 and now number over 7,000 a year as a result of rising rates in developing countries, particularly Africa and the Indian subcontinent, and increasing travel to and from these countries. Case rates in the white UK-born population are around three in 100,000 a year, while rates in those born in India are 65 times and in those born in Africa 120 times higher.
Populations in areas with rapid demographic change are vulnerable to TB. The highest incidences are in central Africa, where death rates exceed 200 per 100,000 each year, and southern Asia, particularly India.
The population of India is likely to increase by 75 per cent in the next 100 years, and some central African countries such as Malawi may rise by 250 per cent. The demographic increase alone will account for 75 per cent of the increase in cases over the next decade.
2. MAKING A DIAGNOSIS
Infection is acquired from airborne droplets from an 'open' case. The initial, primary infection may be subclinical, or accompanied by low-grade pyrexia and mild respiratory symptoms.
In 90 per cent of such cases the lesion heals and remains inactive. The only evidence will be that the tuberculin skin test is converted from negative to positive: so-called latent tuberculous infection.
Enlarged lymph glands may occlude a major airway in the lung, causing lobar collapse. A pleural effusion may develop. Rarely, the bacteria may disseminate to cause miliary disease characterised by a fine nodular shadowing on the chest X-ray, or to non-respiratory sites such as the bones, GU system, abdomen or meninges.
A chest X-ray may show any of these features as well as unilateral hilar and paratracheal lymphadenopathy.
Like primary TB, post-primary TB may be asymptomatic, presenting on screening or routine chest X-ray. More commonly it may present with non-specific constitutional or specific respiratory symptoms that can also occur in other chest diseases.
The most common symptom of TB is a persistent irritating cough, usually productive of phlegm. Haemoptysis may occur. Malaise is usual, fever normally low grade.
Weight loss may be dramatic and profuse night sweats are common. Breathlessness is a late feature, except in patients with pre-existing lung disease. Chest pain is uncommon.
Signs include weight loss, pallor and fever, but are often not as evident as X-rays may suggest. Respiratory signs may be absent. A chest X-ray showing fluffy cavitating shadows in the upper zones is characteristic.
Once the diagnosis is suspected, every effort should be made to obtain specimens for smear and culture. Three sputum specimens should be sent for acid and alcohol-fast bacilli (AAFB) staining and culture. Specimens should be obtained from non-respiratory sites if this is the presenting feature.
Only the isolation of M tuberculosis confirms the diagnosis.
3. MANAGEMENT AND PREVENTION
The current recommendation is that four drugs be given for two months: isoniazid, rifampicin, pyrazinamide and ethambutol. Where sensitivities are available and the organism is found to be fully sensitive, only isoniazid and rifampicin need to be continued for a further four months. Combination tablets: rifater and rifinah should be used if possible.
Patients must be warned about common side-effects. Rashes are frequent, and any of them can cause nausea, especially pyrazinamide. Hepatotoxicity can be life-threatening. Clinical rather than biochemical monitoring is advised, and the patient should be told to report any sickness.
Rifampicin is a potent inducer of liver enzymes and patients should be warned about possible drug interactions. In particular, the contraceptive Pill will become ineffective.
Once the diagnosis has been established and treatment started, most patients can be managed at home.
The WHO recommends that drugs be given under directly observed therapy (DOT). In the UK, therapy administered by the patient is preferred, but DOT is used selectively.
Once the patient has been started on treatment, the infectivity of sputum usually falls quickly. The infection of any close contacts will have occurred before treatment was started, so isolation has little value unless drug resistance is suspected.
There may be a move towards more DOT, and here GPs and district nurses can play a vital role, while non-medical workers such as pharmacists and social workers may act as observers.
The doctor who makes a diagnosis of TB must notify the proper authorities.
The TB services will then be activated to interview the patient and draw up a list of contacts for screening.
BCG is a weak vaccine giving no more than 80 per cent protection for 15 years. Second and subsequent vaccinations have not been shown to have any protective effect. It is most effective in protecting neonates from disseminated disease.
Because case rates among the 13-30-year-old age group in the white UK population have fallen so low, BCG is no longer given at age 13. It is targeted to high-risk groups at birth such as ethnic minorities and families with a history of TB.
The future TB is out of control in many developing countries. There is also a knock-on effect to developed countries through migration. World powers can re-exert control if the political will is present. Current events would suggest that the situation will deteriorate further before the upper hand is regained in the war against TB.
A GUIDE TO TB
- TB is a world emergency.
- TB is a notifiable disease.
- The number of TB cases in the UK is on the increase due to travel to and from the developing countries.
- The most common symptom of TB is a persistent irritating cough usually productive of phlegm.
- Infection is acquired from airborne droplets from an 'open' case.
- A chest X-ray showing fluffy cavitating shadows in the upper zones is characteristic.
- The current recommendation is that four drugs be given for two months: isoniazid, rifampicin, pyrazinamide and ethambutol.