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!

ObjectivesAfter 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 TBWhat 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)

AfricaAmericasE Medite.SE AsiaW.Pacific,Europeand other

TOTAL

Infected

(x106 )17111752

426574382

1722

Newcases

(x103 )1,400560594

2,4802,560410

8,000

Deaths

(x103)66022016094089040

2,910

*Case fatality

rate0.470.390.270.380.350.10

0.36

Where is the problem?

Everywhere, but particularly in developing countries,

• Where people are immune-compromised, HIV positive or weakened nutritionally.

Risk factorsWho 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

0 50 100

8

7

6

5

4

3

2

1

ProjectedDeaths2000

Deaths1990

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 KongThis 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.