Lecture 27 - TB Epidemiology

Question 1

Proportion of global population with latent TB

Answer 1

~1/3 (~2 billion people)

Question 2

Number of cases of TB disease in 2012

Answer 2

8.6 million

Question 3

Number of TB deaths globally in 2012

Answer 3

1.3 million

Question 4

TB incidence in Australia

Answer 4

7/100,000 people

Question 5

TB incidence in Kwa Zulu Natal

Answer 5

900/100,000 people

Question 6

Major recent factor in TB infections

Answer 6

HIV pandemic

Question 7

Incidence

Answer 7

New cases in a year

Question 8

Prevalence

Answer 8

All cases in a year

Question 9

What effect does TB treatment have on TB prevalence?

Answer 9

Decrease in prevalence, as treatment decreases amount of time that someone has active TB for

Question 10

Effect of HIV infection on TB risk

Answer 10

Increases risk

Question 11

Why is the TB rate in Bangladesh stable?

Answer 11

Relatively low HIV rate

Question 12

HIV and TB rates in Brazil

Answer 12

Both are decreasing

Introduction of ART correlates with decrease in HIV. Decrease in TB follows decrease in HIV

Question 13

HIV and TB rates in South Africa

Answer 13

HIV rate increases

TB rate increases shortly after HIV increase

Question 14

Proportion of global TB cases in South-East Asia

Answer 14

~55%

Question 15

Largest risk factor in Australia for TB

Answer 15

Being born overseas in a TB high-risk country

Question 16

Risk of infection over time in a person born in a high-risk TB country, who has moved to Australia
1)
2)
3)

Answer 16

1) Greatest risk shortly after arriving Australia
2) Incidence decreases, but still is significant 30 years after arriving in Australia
3) Cumulative risk from immigrants from sub-Saharan Africa, South-East Asia reaches 2.5% after 30 years in Australia

Question 17

Contact tracing

Answer 17

If someone has active TB, test their contacts

Question 18

Mean time from exposure of notification of TB infection

Answer 18

53 days

Question 19

Multi-drug resistant TB

Answer 19

Resistant to isoniazid and rifamycin

Question 20

How to distinguish between TB strains
1)
2)
3)
4)

Answer 20

1) Drug resistance
2) Spoligotyping
3) Variable number of tandem repeats (mirutyping)
4) Whole-genome sequencing

Question 21

Highest-resolution technique to distinguish between TB strains

Answer 21

Whole-genome sequencing

Question 22

What is spoligotyping?

Answer 22

Compare mutatable parts of different TB genomes

Question 23

What is variable number of tandem repeats?

Answer 23

Compare parts of TB genomes that have tandem repeats. Compare number. Often compare 24 parts of genome.

Question 24

Beijing strain
1)
2)
3)

Answer 24

1) Common TB strain in SE Asia
2) Only 3-4 different variable number of tandem repeat types circulating
3) Hard to distinguish between strains with VNTR. Have to use whole-genome sequencing

Question 25

Demographic versus personal risk of TB
1)
2)

Answer 25

1) Similar baseline level of personal risk of household contact between Australia, South Africa and Peru slums
2) Extra risk based on prevalence of TB in country

Question 26

Case of TB outbreak in British Columbia
1)
2)
3)

Answer 26

1) Contact tracing of active TB initially identified a baby as the index case
2) This was incorrect, as babies are poor transmitters of TB
3) Original epidemiology done with VNTR of 24 loci. Whole-genome sequencing was used, 2 different TB strains were identified

Question 27

Why would a 100% vaccine given to 100% of the population not eliminate TB?

Answer 27

There are still cases of latent TB that can progress to active TB