Epidemiology of tuberculosis. Peymane Adab, Richard Fielding, Susana Castan.

Who are we? We work in the Department of Community Medicine, University of Hong Kong. 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 known 1. Usually a respiratory disease 2 due to infection by Mycobacterium tuberculosis 3. Mycobacterium tuberculosis 3

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?global 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)

Where is the problem? Everywhere, but particularly in developing countries, Where people are immune- compromised, 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% ).

Mortality rate/100,000 population 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 TB 1 ; 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 migration 1, –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.