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- 1. Epidemiology of tuberculosis. Peymane Adab, Richard Fielding, Susana Castan.
- 2. • Who are we? We work in the Department of Community Medicine, University of Hong Kong.
- 3. Why do a TB lecture? • Because, as you will see, it is one of the most important, readily preventable infectious disease in the world, yet it still kills and sickens millions each year. • That makes it worth doing something about!
- 4. Objectives After this lecture, you should be able to: • describe the epidemiology of TB in terms of time trends, geographical variation and susceptible groups;
- 5. • interpret changes in the epidemiology of TB; • describe the major factors that will affect future trends in TB.
- 6. About TB What is it? •One of the oldest diseases known1. •Usually a respiratory disease2 due to infection by Mycobacterium tuberculosis3.
- 7. Why worry about TB? • Worldwide, one person in three is infected with TB. It kills more than 3 million people annually. Yet it is completely curable and is (relatively) inexpensive to cure.
- 8. How global is TB? • Someone is infected with TB every second; • 33% of the world population is already infected; • 25% of all avoidable deaths in economically productive age groups are due to TB.
- 9. TB world-wide (1990) Africa Americas E Medite. SE Asia W.Pacific, Europe and other TOTAL Infected (x106 ) 171 117 52 426 574 382 1722 New cases (x103 ) 1,400 560 594 2,480 2,560 410 8,000 Deaths (x103 ) 660 220 160 940 890 40 2,910 *Case fatality rate 0.47 0.39 0.27 0.38 0.35 0.10 0.36
- 10. Where is the problem? Everywhere, but particularly in developing countries, • Where people are immune- compromised, HIV positive or weakened nutritionally.
- 11. Risk factors Who are most at risk? • Malnourished, elderly, poor. • Migrants, refugees, travelers. • Smokers, chronic alcoholics. • Those with co-morbidity: diabetes, HIV/AIDS, silicosis.
- 12. Sources of TB information 1. Notification of cases 2. Surveillance 3. Mortality statistics 4. Service activities data
- 13. Changing TB mortality • In the West, decline in TB mortality due to –elimination of poverty –improved nutrition –medical care (streptomycin reduced deaths in UK by 51% 1948-1971).
- 14. Mortality rate/100,000 population 0 50 100 8 7 6 5 4 3 2 1 Projected Deaths 2000 Deaths 1990 Source- WHO Global Health Statistics1996
- 15. Interpreting trends 1: real trends • Environmental: (nutrition, wealth housing,hygiene, sociopolitical). • Host changes: susceptibility (e.g. HIV/AIDS infection), travel, migration, sociodemographics. • Agent changes: Development of drug resistant strains of TB.
- 16. Interpreting trends 2: apparent trends • Changed social attitudes towards TB1; • Improved diagnostic techniques, recognition and awareness; • Improved notification procedures • Availability of health statistics.
- 17. TB Trends • Hong Kong This link provides an interesting historical perspective on TB mortality trends in Hong Kong during the 20th Century.
- 18. TB rates increasing • TB infection rates are projected to increase, due to; –aging populations, –increasing travel and migration1, –increasing drug-resistance, –increasing HIV prevalence.
- 19. Multi Drug Resistant strains of TB (MDR-TB) • MDR-TB is TB resistant to 2 or more main-line anti-TB drugs. • MDR-TB is increasing worldwide • More than 50 million people probably already infected • Poor adherence to treatment
- 20. HIV/AIDS • 1994: Of 14 million people HIV +ve, 40% also had TB. • TB leading cause of death if HIV +ve • weakened immunity increases risk of TB infection progressing to disease. • greater risk of misdiagnosis of TB in HIV and subsequent inadequate treatment.
- 21. • It is estimated that between now and the year 2020 nearly 1,000,000,000 more people will be newly infected, 200 million will get sick and 70 million will die from TB, if control is not strengthened. • The majority of these cases will occur in developing countries
- 22. TB Control and Prevention Main strategies include: • BCG vaccination • Case finding • Effective chemotherapy • Health Education • Chemoprophylaxis
- 23. Summary- TB is: • leading infectious cause of death • infection rates and drug resistant rates increasing, • travel and migration key risk factors • poor, weak and elderly most vulnerable • HIV positive people vulnerable and major threat to future trends.
Editor's Notes
- (1) In March 1882, Dr. Robert Koch discovered Mycobacterium Bacillus, in Germany. At that time TB was very prevalent. (2) This is the most frequent presentation. Extra-pulmonary TB (e.g. miliary, skeletal, meningeal, gastro-intestinal) also occur, particularly in children, immigrants from countries where TB is more common and in people with impaired immunity. (3) Tubercle bacilli are acid alcohol-fast bacilli (AAFB), that means they strongly resist decolourisation with acid or alcohol.
- Many people still die from TB, even though it is curable. It costs about US$2,000 per patient to treat. (The cost for Multi-Drug Resistant-TB rises to more than US$250,000 per patient.) TB control is difficult, which is why it is still an important cause of death. Currently, the principal control strategy for those with TB is contact-tracing and DOT (Directly Observed Therapy, to ensure patients complete treatment ). DOT both maximizes cure-rates and minimizes the risk of encouraging drug-resistant strains of TB bacilli.
- Follow the link to find more about TB, and a map with mortality data.
- E.Medite: Eastern mediterranean W. Pacific: excludes Japan, Australia, New Zealand Americas excludes USA and Canada Other (including USA, Japan, Australia, New Zealand) In 1990 prevalence of TB was 1,722,000,000; Incidence 8 million. *death/incidence ratio. 95% of new cases were in developing countries 5%, in developed countries.
- Follow the link to the WHO Global Program for TB control. Strategies for control depend on many factors including: the level of development, the economy and the incidence and prevalence of TB in each country.
- Historically, children under 5 years old were also at risk of TB. However, their risk has been markedly reduced since the introduction of BCG vaccination.
- 1. TB one of the most important notifiable diseases worldwide. Notifications are the most important source of data for following the epidemiology of TB and for initiation of contact tracing. 2-4. Surveillance includes monitoring death certificates, or contacts with health services used by patients with TB: chest clinics, outpatient clinics, hospital admission, other health facilities. All these sources have certain limitations in terms of accuracy and completeness. In particular, developing countries tend to have more basic health services and also poorer information. Data on TB, especially morbidity, are likely to be underestimates.
- However, it is not all good news. TB is on the increase among the growing numbers of homeless peoples in Europe and America, among the poorest living in economies under transition, such as in E. Europe. Also, those countries experiencing war or other politically-determined privations where disease surveillance and treatment have been disrupted, such as, currently, Afghanistan and Iraq, are probably seeing an increase in TB infections and deaths.
- A majority of deaths from TB occur in India (4), sub-Saharan Africa (1) and Asia (3). Latin America (5), China (8) and the Middle East (2) have moderate levels compare to established economies (7). Rates are increasing in some of the formerly socialist economies (6), such as Russia. India faces growing mortality from TB. The link between high mortality from TB and poverty is apparent from these data which exclude projected increases in mortality attributable to co-morbidity, including a growing HIV prevalence in some countries (particularly sub-Saharan Africa).
- A real change in disease incidence or mortality can occur due to changes in the environment, in the host or in the agent.
- Apparent changes in incidence or mortality can occur over time (apparent trend) without real changes in actual rates. It is very important to consider these influences when analyzing trends. (1) In 19th C. Europe TB was common and “consumption” a trendy, though tragic cause of death. In the operas La Boheme and La Traviata, both heroines die from TB, while the Romantic poet Shelley also succumbed. In the Oslo Art Gallery, a 19th C. painting “The Sick Child” depicts a young girl clearly dying from TB.
- Follow the link to a chart illustrating the changing pattern of TB related deaths in Hong Kong and how this relates to different historical socio-political events. In China, TB remains a feared and stigmatizing disease. It was a major killer in the 19th C. and the early 20th C. when western colonial ambitions and corruption bankrupted the nation. Contrast this image to that of TB in 19th Century Europe!
- World travel is increasing annually, also refugees and forced migrations are increasing due to regional wars, economic downturn or opportunities elsewhere. (1) At the turn of the 19th century an epidemic of TB on the Eastern Seaboard of the USA was due to waves of European immigration into cheap slum housing. So great was the demand for passages to the US that a whole fleet of fast steamships were built. The most famous of these was The Titanic. Had the Titanic not sank, many of her steerage passengers would have reached New York, and a new life, only to die of TB.
- Poor control and prevention programs, and incomplete treatment adherence, have contributed to emergence of MDR-TB strains. Remember the importance of DOT to guarantee adherence to treatment. In the west, MDR-TB is most common among homeless people in urban centres such as New York, London and Paris.
- In the 1980s, New York City discontinued TB surveillance and treatment programs introduced in the 1920’s to control the TB epidemic, then decimating the slum immigrant populations. At the same time HIV incidence began to rapidly increase. The result has been a rapid upswing in the incidence of TB during this decade, mainly among, but not limited to, HIV positive people, a significant proportion of which is MDRTB.
- The global burden of TB is inestimable. The majority of people getting TB will be those who can least afford weeks or months of sickness, the breadwinners of families who will die and leave unsupported dependents.
- In order to reverse the increasing trend in TB, effective control and prevention is required in all countries.
- As can be seen from some of the little historical vignettes we have presented, TB has been a major influence on shaping the human world. It looks like it will continue this habit well into the 21st Century! Further reading: Science, medicine and future. BMJ 1998;316:1962-64. TB: story of medical failure. BMJ 118;317:1260.