Download 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
Africa
Americas
E Medite.
SE Asia
W.Pacific,
Europe
and other
171
117
52
426
574
382
1,400
560
594
2,480
2,560
410
660
220
160
940
890
40
*Case
fatality
rate
0.47
0.39
0.27
0.38
0.35
0.10
TOTAL
1722
8,000
2,910
0.36
6
New Deaths
cases
3
3
(x10 ) (x10 ) (x10 )
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
Projected
Deaths
2000
Deaths
1990
2
3
4
5
6
7
8
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
1
TB ;
• 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.