Epidemiology study of tuberculosis
Aims
You are going to study epidemiological data to identify trends. You will also consider the benefits of
studying and using this type of data.
Setting the scene
Epidemiology is the study of epidemics, which is the widespread occurrence of infectious diseases. One
such disease is tuberculosis (TB) which is caused by a type of bacteria called Mycobacterium
tuberculosis (or M. tuberculosis for short).
TB can affect the lungs and is passed from person to person through the air. It can cause coughs, chest
pains, and sometimes the infected person can cough up blood from deep in their lungs. People with
these TB symptoms can be treated with antibiotics, or it can be prevented with a BCG vaccine.
If it is not treated, those who show these symptoms could die. Some people carry TB but do not develop
these symptoms, because their immune system keeps the bacteria under control. These people are not
infectious.
Questions
1 a Explain what is meant by ‘disease’.
A disease is a condition that is caused by the body not functioning properly. It can
affect the body physically and mentally.
(1 mark)
b
Explain the difference between communicable and non-communicable diseases.
If a disease is communicable it can be spread between organisms which are caused by
microorganisms whereas if a disease is non communicable it doesn’t spread and only
affects that one person or thing that has that disease
(4 marks)
2
The table below shows the number of deaths from TB in England and Wales from 1855 to 1955.
Year
Number of deaths from TB (per
100 000 of the population)
Year
Number of deaths from TB (per
100 000 of the population)
1855
296
1915
114
1860
278
1920
116
1865
274
1925
88
1870
269
1930
no data
1875
241
1935
67
1880
225
1940
51
1885
200
1945
59
1890
182
1950
47
1895
165
1955
14
1900
149
1960
1905
133
1965
1910
118
1970
a
Plot a line graph to show this data.
b
i
Describe the trend in the data.
The trend slowly decreases.
(1 mark)
ii
Suggest an explanation for this trend.
Because they found a cure for the disease, so the deaths decreased
(1 mark)
c
For each of the following, explain whether or not it affected the trend in deaths from TB and
suggest a reason for this.
i The discovery in 1882 of M. tuberculosis, the bacterium that causes TB
This affected the trend of the deaths from tuberculosis because without
the discovery of the bacterium that caused the virus they would not be able to
make a vaccine and cure the virus.
ii
World War I in 1914 – 1918
The deaths slowly decreased at the time of the war.
(2 marks)
iii World War II in 1939 – 1945
The deaths were decreasing quicker than before.
(2 marks)
iv The development in 1944 of the first effective antibiotic against TB
The development of the antibiotic made the deaths rapidly decrease.
(2 marks)
3
The table below shows the number of people identified with TB, and the percentage of people
identified with human immunodeficiency virus infection and acquired immune deficiency syndrome
(HIV/AIDS) in South Africa, between 1990 and 2006.
(The first officially reported HIV/AIDS case in South Africa was in 1982, but data for the population as
a whole is only available from 1990.)
a
Year
Number of people identified
with TB
(per 100 000 of the
population)
Number of people identified
with HIV
(as a percentage of the
population)
1980
185
data not available
1982
200
data not available
1984
192
data not available
1986
154
data not available
1988
183
data not available
1990
222
0.7
1992
199
2.0
1994
211
7.6
1996
293
14.3
1998
333
19.7
2000
333
24.5
2002
495
26.5
2004
592
29.5
2006
626
29.1
Plot this data as two lines on the same graph. Use two y-axes. Use the y-axis on the left to plot
the data for TB, and a y-axis on the right to plot the data for HIV.
(8 marks)
b
i
Describe the trends in the data.
(4 marks)
ii
Describe the evidence for there being a correlation between the incidence of TB and that
of HIV/AIDS.
(2 marks)
iii HIV/AIDS affects the immune system therefore it is not so able to fight infection. Use this
information, as well that in the Setting the scene section above, to suggest a possible
explanation for a correlation between TB and HIV/AIDS.
(3 marks)
4
Suggest four reasons why it is important to collect and study data, such as that shown in your
graphs.
(4 marks)
5
Look at the graphs you have drawn.
a Compare the trend for TB in South Africa with the trend for TB in England and Wales.
(1 mark)
b
Suggest two reasons for these different trends.
(2 marks)
c
Is it valid to compare these two trends?
(2 marks)
Student follow-up
1
In the UK, the vaccine against TB (called the BCG vaccine) is not automatically given as part of the
normal National Health Service (NHS) vaccination schedule. It is offered shortly after birth,
particularly to children in high risk areas thought to have an increased risk of coming into contact with
TB, or who have parents or grandparents born in a country where there is a high rate of TB.
a Suggest why the BCG vaccination is not automatically given to all babies in the UK as part of the
normal NHS vaccination schedule.
(2 marks)
b
The BCG vaccination is sometimes given to adults. Suggest two reasons why it might be given
to an adult in the UK.
(2 marks)