Epidemiology of Tuberculosis

Epidemiology of tuberculosis. Peymane Adab, Richard Fielding, Susana Castan. • Who are we? We work in the Department of Community Medicine, University of Hong Kong. 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! Objectives After this lecture, you should be able to: • describe the epidemiology of TB in terms of time trends, geographical variation and susceptible groups; • interpret changes in the epidemiology of TB; • describe the major factors that will affect future trends in TB. About TB What is it? • One of the oldest diseases known1. • Usually a respiratory disease2 due to infection by Mycobacterium tuberculosis3. 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. 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. TB world-wide (1990) Infected 6 New Deaths cases 3 3 Africa Americas E Medite. SE Asia W.Pacific, Europe and other TOTAL (x10 ) (x10 ) (x10 ) 171 117 52 426 574 382 1722 1,400 560 594 2,480 2,560 410 8,000 660 220 160 940 890 40 2,910 *Case fatality rate 0.47 0.39 0.27 0.38 0.35 0.10 0.36 Where is the problem? Everywhere, but particularly in developing countries, • Where people are immunecompromised, HIV positive or weakened nutritionally. Risk factors Who are most at risk? • Malnourished, elderly, poor. • Migrants, refugees, travelers. • Smokers, chronic alcoholics. • Those with co-morbidity: diabetes, HIV/AIDS, silicosis. Sources of TB information 1. Notification of cases 2. Surveillance 3. Mortality statistics 4. Service activities data 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). Mortality rate/100,000 population 1 2 3 4 5 6 7 8 Projected Deaths 2000 Deaths 1990 0 50 100 Source- WHO Global Health Statistics1996 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. Interpreting trends 2: apparent trends • Changed social attitudes towards TB1; • Improved diagnostic techniques, recognition and awareness; • Improved notification procedures • Availability of health statistics. TB Trends • Hong Kong This link provides an interesting historical perspective on TB mortality trends in Hong Kong during the 20th Century. TB rates increasing • TB infection rates are projected to increase, due to; –aging populations, –increasing travel and migration1, –increasing drug-resistance, –increasing HIV prevalence. 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 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. • 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 TB Control and Prevention Main strategies include: • BCG vaccination • Case finding • Effective chemotherapy • Health Education • Chemoprophylaxis 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.