Tuberculosis (TB) is the world's leading cause of morbidity and mortality from a single organism. The World Health Organisation estimates that the disease kills around 3 million people a year, with 7.3 million new cases annually. student EHO Alastair Tomlinson researched the distribution and determinants of the disease in Cardiff, here are his findings

TB is caused by the bacteria Mycobacterium tuberculosis - the tubercle bacillus. Other organisms that are occasionally implicated are Mycobacterium africanum (from humans), and Mycobacterium bovis (from cattle).(3) For many years, developed countries had shown downward trends of mortality and morbidity, but morbidity has plateaued, even increasing in certain populations, such as those with a high prevalence of human immunodeficiency virus (HIV) infection.(3) Infection occurs when a susceptible person inhales bacteria in airborne droplets, produced by persons with pulmonary or laryngeal TB during coughing, laughing, or sneezing.(3) The organisms can survive in house dust and air for long periods. The probability of acquiring TB increases as the concentration of organisms in the air increases, which highlights the importance of good ventilation as a control and prevention tool.

Tuberculosis is a notifiable disease under the Public Health (Infectious Diseases) Regulations 1988. Any registered medical practitioner, who becomes aware or suspects that a patient is suffering from a notifiable disease, must notify the proper officer of the local authority with the details of the case.1 The data used for this study has been obtained in this way, using all notifications of new cases of tuberculosis in Cardiff from 1988-1997. Tuberculosis data for England and Wales has been obtained from the Public Health Laboratory Service (PHLS).

The period 1988-1997 was chosen to provide a large enough number of cases to be able to carry out meaningful statistical analysis. During this 10-year period, 289 cases of tuberculosis were reported to Cardiff County Council. Cases were distributed across all age groups, with the highest incidences occurring in the more elderly age groups, peaking at the 65-74 age group (17.7 cases per 100,000 per year). The rates broadly match those for England & Wales as a whole. The rates show that more men than women contract tuberculosis in Cardiff (62.3 per cent to 37.7 per cent), a trend that holds for England and Wales as well. A national survey of TB notifications in England and Wales in 1988 found that middle-aged and elderly men continue to experience much higher rates of TB than women.(11)

The incidence of cases by the week of notification was also analysed to assess the degree of seasonal variation in TB notifications, but there were no significant seasonal peaks or troughs, indicating that the time of year has no significant bearing on TB incidence. Incidence rates were calculated for Cardiff and England and Wales as a whole, including an age-standardised morbidity ratio for the whole of Cardiff. In terms of a crude incidence rate, Cardiff fares better than the whole of England and Wales with 10.1 cases per 100,000 per year against 11.6, but it has a marginally higher age-standardised ratio (101, compared to 100). There are 1.5 less cases each year per 100,000 population in Cardiff than in the whole of England and Wales, according to the incidence rate. The morbidity ratio, which is in arbitrary units, shows that 1 per cent more cases occurred in Cardiff than were expected.

In Cardiff, data according to residence has been organised by electoral ward, allowing comparison of TB data with a range of other data relating to electoral wards in Cardiff. The general incidence rate for the majority of the wards is around 10 cases per 100,000 per year. However, three wards have much higher rates - Grangetown, Riverside and Butetown - all inner city areas, with large ethnic minority populations. The incidence rates per year for these wards are as follows: Butetown - 64.2 cases per 100,000; Grangetown - 29.0 cases per 100,000; Riverside - 34.6 cases per 100,000. A previous study also found similar results.(10)

Information on ethnic group was not routinely collected as part of the notification system until January 1999. However, five-yearly national surveys of tuberculosis have been taking place, the most recent being 1998. These gather additional data about cases, such as country of birth, ethnic group, date of entry to the UK, and other details relating to previous treatment. Data was available for 1998, and Bro Taf Health Authority had undertaken a local extended survey on an informal basis for 1996 and 1997. So data on ethnic group was available for a period of three years - 102 notified cases. Of these cases, 59 notifications actually contained the necessary data on ethnic group, and Table 2 has been produced using this information. While the low number of cases means that no great weight can be placed on this data, it does indicate which ethnic groups are at the most risk.

DEPRIVED AREAS
Butetown is home to the largest Somali community outside of Somalia, while Riverside and Grangetown both have high Asian populations. All of these communities are from regions classed as high-prevalence by the IWGT.8 The 1988 national survey found that people of Indian subcontinent ethnic origin (ie Indian, Pakistani, or Bangladeshi) were between 25 and 30 times more likely to catch TB than their Caucasian counterparts.(11) Similar results also indicated by the limited Cardiff data show that people from the subcontinent are around 40 times more likely to contract the disease. Black groups are around 12 times more likely to catch the disease, and people from Chinese and other ethnic groups are around 19-20 times more likely to contract TB. The high population of ethnic minority groups in Riverside, Grangetown and Butetown could therefore partially explain the similarly high tuberculosis incidence in those wards. Other environmental factors also influence the incidence of tuberculosis. TB has been previously linked to social deprivation, both in Cardiff and in general.(10,12)
The Census in 1991 collected data on five social deprivation indices:

• Households with three or more children and no earner
• Overcrowded households
• Lone parent households
• Households without a car
• Households lacking basic amenities

Table 3 shows the 10 most socially deprived wards in Cardiff according to the five indices used. As the table shows, Butetown, Grangetown, and Riverside are among the most socially deprived areas of Cardiff. It can be extremely difficult to distinguish the effects of social deprivation and ethnic group on TB incidence.(5) Studies have achieved contrasting results. In Leeds, Goldman et al found that although incidence was higher amongst Asian children than in white children, it was greater in the most deprived areas of the city independent of race.(7) However, another recent study by Doherty et al showed race was a more important factor than poverty in the difference in rates across the boroughs of London.(6) Nonetheless, it would appear that the high incidence of TB in Butetown, Grangetown and Riverside could be put down to a combination of social deprivation and high populations of ethnic minority. However it cannot be automatically assumed that there is any systematic relationship between the distribution of social and ethnic characteristics in the wards, and the distribution of characteristics amongst those persons living in the wards who have TB.

The data available from the notifications could not establish whether any link existed between TB incidence and homelessness or residence in an institution such as a prison or temporary hostel. Previous studies have shown that these groups should also be considered to be at higher risk of TB infection than the rest of the population.(4,9) It is necessary to identify those groups and communities in Cardiff who are at highest risk from TB. Clancy et al (1991) suggested some benchmarks for use when classifying TB risk, based on incidence per 100,000 per year. According to these classifications, no group in Cardiff is classed as high risk. However, the Indian subcontinent ethnic group is only slightly below this class (at 96.5 cases per 100,000), and Butetown as a ward has an incidence of 64.2 cases per 100,000.

Clearly any effective prevention and control strategy must address the chief risk factors, but the needs of the wider population should also be taken into account. A joint approach between Bro Taf Health Authority and Cardiff County Council is necessary to combat the disease. The majority of control and prevention measures are exercised by the health authority, including case identification and diagnosis, notification, contact tracing, treatment, chemoprophylaxis and immunisation. But the importance of public health measures in TB control should not be underestimated. TB mortality was already falling rapidly before Robert Koch identified the TB bacillus in 1882. By 1940, mortality was nearly 10 times lower than the level a century before - all prior to the discovery of effective chemotherapy and the BCG vaccine. This has been put down to general improvements in nutrition, sanitation and social conditions, and indicates the crucial role public health interventions have to play in TB control.(2)

Cardiff CC has a major influence on the quality of housing conditions, both in its role as a social landlord, and in its enforcement role in private sector housing (through the environmental protection department). By focusing resources into poor housing areas, the council can have a major impact on the standard of housing. The knock-on effect of this will help contribute to a reduction TB incidence, particularly when combined with other programmes detailed above. Riverside is already the subject of a housing renewal area, aiming to improve the quality of environmental and social conditions in the area. The housing enforcement division is also looking at focusing resources on particular areas, including Grangetown and parts of Butetown. The council owns many lodging houses in Butetown, and these should be looked at urgently, to ensure that social conditions are adequate. The council can also have an influence on social deprivation through planning and economic development. These measures should be used to encourage investment in deprived areas, providing extra jobs, services and commerce, leading to an improvement in the social status of the area.

Health promotion staff in the local authority also have a role to play by getting involved in education programmes and encouraging people to make use of local health services. Increasing awareness among the public may result in higher levels of presentation of cases to GPs, enabling the contact tracing and control procedures to take place. Education programmes should cover the symptoms of TB, and should strongly emphasise the treatable nature of the disease. It should also mention the steps to be taken if someone suspects that they have TB. Links should be established with those working with high-risk groups, to make them aware of TB symptoms, to enable quick identification and treatment of cases.

Where health services are not locally available, the local authority should consider providing transport, either through the existing public bus system or by community transport services. Data highlighting the high-risk groups and areas can also be used as a lever to gain extra resources, by presenting the purse-holders of the council with evidence that certain areas or schemes need further investment.

TB is still a problem at the end of the 20th century, contrary to the opinions of some parents and healthcare professionals as Kynch found (for example, "There is no TB any more"... "We don't do BCG any more... the doctor says it is the same in the whole country").(10) Although in Cardiff the general incidence and age-standardised rates are normal for England and Wales, certain groups are at much higher risk. The schemes detailed in the strategy above would help to further the battle against TB in Cardiff, although the WHO estimated in 1993 that there would be no reduction in TB in low-prevalence countries over the next decade.

ACKNOWLEDGEMENTS
The author wishes to thank Dr Meirion Evans of Bro Taf Health Authority for making the notification data available; also Will Lane and Dennis Gardner (Cardiff County Council) for their assistance and advice; and Neil Roche in Cardiff Research Centre for the provision of the social deprivation data. Thanks also to Liz Weekes in the BCG Unit at Llandough Hospital for her help and assistance.

REFERENCES
1. Bassett, 1995
2. Beaglehole R., Bonita R. & Kjellstrom T. Basic epidemiology, WHO, Geneva 1993.
3. Benenson A.S. [Ed.] Control of communicable diseases in man (16th edition), American Public Health Association, 1995.
4. Citron K.M., Southern A. & Dixon M. Out of the shadow, Crisis, London, 1995.
5. Darbyshire J.H. "Tuberculosis: old reasons for a new increase?", British Medical Journal Vol. 310 pp 954-5, 1995.
6. Doherty M.J., Tocque K., Bellis M.A., Spence D.P.S., Williams C.S.D. & Davies P.D.O. "Tuberculosis notifications in England: the relative effects of poverty and ethnicity", Thorax Vol. 50 (Supplement 2) p A60, 1995.
7. Goldman J.M., Teale C., Cundall D.B., & Pearson S.B. "Childhood tuberculosis in Leeds, 1982-90: social and ethnic factors and the role of the contact clinic in diagnosis", Thorax Vol. 49 pp 184-5, 1994.
8. IWGT (Interdepartmental working group on tuberculosis) The prevention and control of tuberculosis in the United Kingdom: recommendations for the prevention and control of tuberculosis at local level, Department of Health/Welsh Office, 1996.
9. Kumar D., Citron K.M., Leese J. & Watson J.M. "Tuberculosis among the homeless at a temporary shelter in London: report of a chest x-ray screening programme", Journal of Epidemiology and Community Health Vol. 49 pp 629-33, 1995.
10. Kynch J. Poverty, unemployment and tuberculosis: An investigation of Cardiff TB cases 1984-1992, University College of Swansea (unpublished), 1993.
11. MRCCEG (Medical Research Council Cardiothoracic Epidemiology Group) "National survey of notifications of tuberculosis in England and Wales in 1988", Thorax Vol.47 No. 10 1992 pp 770-775, 1992
12. Spence D.P.S., Williams C.S.D., Hotchkiss J. & Davies P.D.O (1992), "Tuberculosis and poverty", Thorax Vol. 47 p 849
Further reading
CDC DTBE (Center for disease control - division of TB elimination), Frequently asked questions about TB, CDC, USA, 1999. www.cdc.gov/nchstp/tb/faqs/qa.htm
Mims C., Playfair J.H.L., Roitt I.M., Wakelin D., Williams W. Medical microbiology, Mosby-Year Book Europe, London, 1993.
Public Health Laboratory Service, Facts and figures - tuberculosis notifications by gender and age group, England and Wales 1982-1997, PHLS, UK, 1999. http://www.phls.co.uk/facts/
WHO "Estimates of future global tuberculosis morbidity and mortality", Morbidity and Mortality Weekly Review Vol. 42 p 49, 1993.
WHO The World Health Report 1998 - Life in the 21st century: A vision for all, WHO, Geneva, Switzerland, 1998.