Respiratory Infections

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Respiratory Infections

Tuberculosis

Causative Agent

Tuberculosis (TB) is a disease caused by Mycobacterium tuberculosis, M. bovis, M. africanum, M. canetti or M. microti, which together form the Mycobacterium tuberculosis complex.

Clinical Description

There are two forms of tuberculosis: TB affecting the lungs and TB causing infection elsewhere in the body. The symptoms that occur when TB disease develops are usually not very specific. Often there are complaints of tiredness, listlessness, loss of weight and night sweating. When TB affects the lungs, a cough is usually present for weeks or even months.

Infection may be confirmed by bacteriological or pathological examination of tissues or specimens; alternatively the diagnosis may be based on clinical or radiological features of the disease. A diagnosis may also be made at post mortem examination.

Transmission

Transmission of TB is by inhalation of infected droplets and requires prolonged close contact (e.g. sharing sleeping quarters) with an infected individual. An important feature of TB is that after infection, the bacteria can remain latent in the body for a long time (even lifelong) causing no symptoms of disease. People with latent TB infection are not infectious. Under favourable conditions, the bacteria can start multiplying and cause clinical disease.

Surveillance in Scotland

The Scottish Mycobacteria Reference Laboratory (SMRL) undertakes the identification (including molecular characterisation) and susceptibility testing of all mycobacterial isolates in Scotland , both for clinical management and for epidemiological purposes. The laboratory reports all identification results weekly to HPS, provides epidemiological information as requested and publishes an annual report.

The establishment of the Enhanced Surveillance of Mycobacterial Infections (ESMI) scheme in 2000 represented a major development in the surveillance of tuberculosis in Scotland . Co-ordinated by HPS, the scheme incorporates the European minimum dataset and provides feedback to the various agencies involved in the diagnosis, treatment and control of tuberculosis.

Notification

Tuberculosis is a notifiable disease under the Public Health etc. (Scotland) Act 2008. More information on the Public Health etc. (Scotland) Act 2008 is available from the Scottish Government website.

Trends in Scotland (1995-2011)

Unlike some other areas of the UK and Europe, Tuberculosis in Scotland has been relatively stable over the past 20 years (as shown in the notifications data). However, since 2005 there has been an increasing trend in TB in Scotland, particularly people presenting with non-pulmonary disease and among people that were born outwith the UK . Age specific incidence shows increasing trends in those aged 25-34 years and those aged 65 years and over.

Incidence and Risk

The incidence of TB in Scotland is generally stable and low, with around 8-9 cases per 100,000 population. Currently there are around 285 cases of pulmonary TB and 180 non-pulmonary TB cases reported per year. TB is given as the underlying cause of death in around 40 people each year in Scotland. Dramatically rising rates in other parts of the world (particularly sub-Saharan Africa, Asia and South America) have caused TB to be declared a global emergency by the WHO.

Global Incidence

The World Health Organisation estimates that about a third of the world's population is infected with Mycobacterium tuberculosis, about nine million new cases of tuberculosis disease occur each year, causing nearly two million deaths each year. The number of new cases of TB disease continues to increase, particularly in Africa, the Eastern Mediterranean and South-East Asia. Factors contributing to this include the increasing population, migration from rural to urban areas with associated poverty and poor social conditions, deterioration of the public health infrastructure needed to control tuberculosis, drug resistant TB and the HIV epidemic.

Individuals arriving in the United Kingdom from countries deemed to be at high risk (greater than or equal to 40 new cases per 100,000 population per annum) require screening. Information on estimates of incidence by country can be found on the HPA website.

Prevention

Long-term prevention is by BCG (Bacille Calmette Guérin) vaccination, which uses an attenuated strain of M. bovis and should be considered for infants that are tuberculin skin test negative and are at risk from exposure to patients with sputum positive pulmonary tuberculosis. It mainly gives protection against severe forms of the disease, like TB meningitis and miliary TB, in children under five years of age.

In the UK , like many other countries, BCG is offered to babies who are more likely than the general population to come into contact with someone with TB. This is because they either lived in an area with high rates of TB, or their parents or grandparents came from a country with high rates of TB (see the HPA Website for a list of high-incidence countries). The vaccine is usually offered soon after the birth. More information about BCG vaccination and the recommendations for the vaccine is available in the Immunisation against infectious disease - 'The Green Book' .

Chemoprophylaxis using anti-tubercular drugs is also used to prevent the development of infection, or to prevent the progression of infection to manifest disease (usually on the basis of a positive tuberculin reaction).

A TB Action Plan for Scotland

The recent increasing trends in TB led the Scottish Government, in collaboration with HPS, to produce A TB Action Plan for Scotland to ensure that Scotland provides the best quality clinical, laboratory and public health services and that these are underpinned by the best possible surveillance and epidemiology in order to reduce the burden of ill-health caused by TB.

Notifications of respiratory tuberculosis cases and incidence to ESMI, 2000-2011*

Year Number of cases Incidence (per 100,000 population) Annual change in numbers (%) Annual change in incidence (%)
2000
403
8.0
-
-
2001
351
6.9
-12.9
-13.8
2002
393
7.8
12.0
13.0
2003
367
7.3
-6.6
-6.4
2004
392
7.7
6.8
5.5
2005
365
7.2
-6.9
-6.5
2006
381
7.5
4.4
4.7
2007
410
8.0
7.6
5.7
2008
445
8.6
8.5
8.0
2009
486
9.4
9.2
8.8
2010*
503
9.7
3.5
3.2
2011*
453
8.6
-9.9
-11.3

*Data for 2010-11 are provisional and may be subject to change

 

Number of tuberculosis cases and incidence by age group, 2011


graph of number of tuberculosis cases and incidence by age group, 2009

 

Last reviewed: 17 May 2013