Tuberculosis (TB) is a disease caused by the tubercle bacillus Mycobacterium tuberculosis. TB usually affects the lungs (pulmonary), but can affect other parts of the body (extra- pulmonary) such as the lymph nodes, the bones and (rarely) the brain.
TB in humans can also occasionally be caused by another bacterium, Mycobacterium bovis, which is particularly associated with infection in cattle and is usually transmitted to humans through contaminated milk.
However,the current risk posed by M. bovis to human health in the UK is considered negligible due to effective controls through milk pasteurisation and tuberculin screening of herds to identify infected animals.
Usually only the pulmonary form of TB is passed onto others and only some people with pulmonary TB are infectious. These are ‘sputum smear positive’ (or 'open') meaning that the germ can be seen with a microscope in a suitably prepared slide of the sputum. They usually cease to be infectious after a couple of weeks of treatment.
Transmission occurs through breathing in air-borne droplets containing bacteria released when an infectious person coughs, talks or sneezes. The risk of becoming infected usually requires close and prolonged contact with a sputum smear positive individual such as living in the same household.
Who gets it and how serious is it?
Anyone can get infected with TB but it is difficult to catch. TB is potentially a very serious disease and can be fatal. It causes more deaths worldwide than any other single infectious disease; nearly two million deaths are estimated to be due to TB annually, mostly in developing countries.
TB is curable with a full course of treatment.
Infection with TB does not necessarily lead to disease. In fact most people who have TB infection will never develop TB disease as the immune system stops the bacteria from multiplying and so it remains dormant or ‘inactive’ in the body, sometimes for life. These people will remain well and are not infectious.
However, there is always the potential for the bacteria to become ‘active’ (start multiplying) and to cause disease if the immune system becomes less effective.
People most at risk of becoming ill with TB when exposed to it are those which fall into one or more of the following groups:
- Are in very close contact with infectious people
- Are HIV-positive
- Live in overcrowded, poor housing
- Dependent on drugs or alcohol
- In chronic poor health
The disease develops slowly in the body, and it usually takes several months for symptoms to appear.
Any of the following symptoms may suggest TB:
- Fever and night sweats
- Persistent cough
- Losing weight
- Blood in sputum (phlegm or spit) at any time
There are very effective treatments available to cure TB, which are usually combinations of specific antibiotics which must be taken for at least six months.
The emergence of TB strains resistant to certain drugs used in the treatment of TB is an increasing problem worldwide, most particularly in developing countries. TB strains classed as multi-drug resistant (MDR-TB) and extensively drug resistant (XDR-TB) are much harder to treat but account for only a very small proportion of cases seen (about 1%) in the UK.
Early detection, especially of infectious cases, is important in reducing the transmission of the disease to others. Prompt and complete treatment is vital in preventing disease relapse, the development of drug-resistant strains, prolonged infectiousness and preventable death.
Identifying cases who have been infected through screening contacts and offering preventive treatment to reduce the risk of infected persons developing TB also contributes to preventing TB.
The BCG vaccination can offer some protection against TB but overall, BCG vaccination plays a limited role in TB control. The schools' programme nationally has been replaced with a programme of targeted vaccination for those individuals who are at greatest risk.
The new programme identifies and vaccinates babies and older people who are most likely to catch the disease, especially in those living in areas with a high rate of TB or whose parents or grandparents were born in a country where TB is common (i.e. 40 or more cases in 100,000 of the population per year).
How common is it?
TB in Wales, and in other industrialised countries, declined rapidly during the 20th century due mainly to better living conditions and the development of effective treatments but never completely disappeared.
Nearly all countries in the world are now affected by the global resurgence of TB driven primarily by increasing poverty and poor access to health services, migration and HIV.
However, TB remains rare in Wales and in the UK as a whole. TB rates remained relatively stable between 1999-2010 in Wales at between 150 and 220 cases per year.
In 2012, the annual number of cases of tuberculosis in residents of Wales was 136. Similar to the rest of the UK, the majority of cases were reported from urban areas, with the rate per 100,000 population highest in young adults. There has also been an increase in the proportion of cases born outside of the UK, originating from high tuberculosis burden countries.
More information about the rates and surveillance of tuberculosis can be obtained from the Public Health Wales Health Protection Division microsite by following the link: rates and surveillance of tuberculosis in Wales
Minimising the impact in Wales
One important role of Public Health Wales is the collection and interpretation of data about the levels of infectious disease in the Welsh population. Key infections, including tuberculosis, are under constant surveillance, to detect significant trends, to evaluate prevention and control measures and to alert appropriate professionals and organisations to infectious disease threats.
All cases of TB are offered appropriate medical treatment and, as the disease can be infectious, screening of close contacts is also undertaken and any necessary treatment or vaccination given.
In addition, the Public Health Wales Tuberculosis programme and the specialist reference mycobacteriology laboratory in South Wales also contribute to the effective diagnosis, surveillance and control of TB in Wales.