Lecture 27 - TB Epidemiology Flashcards
Proportion of global population with latent TB
~1/3 (~2 billion people)
Number of cases of TB disease in 2012
8.6 million
Number of TB deaths globally in 2012
1.3 million
TB incidence in Australia
7/100,000 people
TB incidence in Kwa Zulu Natal
900/100,000 people
Major recent factor in TB infections
HIV pandemic
Incidence
New cases in a year
Prevalence
All cases in a year
What effect does TB treatment have on TB prevalence?
Decrease in prevalence, as treatment decreases amount of time that someone has active TB for
Effect of HIV infection on TB risk
Increases risk
Why is the TB rate in Bangladesh stable?
Relatively low HIV rate
HIV and TB rates in Brazil
Both are decreasing
Introduction of ART correlates with decrease in HIV. Decrease in TB follows decrease in HIV
HIV and TB rates in South Africa
HIV rate increases
TB rate increases shortly after HIV increase
Proportion of global TB cases in South-East Asia
~55%
Largest risk factor in Australia for TB
Being born overseas in a TB high-risk country
Risk of infection over time in a person born in a high-risk TB country, who has moved to Australia
1)
2)
3)
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
Contact tracing
If someone has active TB, test their contacts
Mean time from exposure of notification of TB infection
53 days
Multi-drug resistant TB
Resistant to isoniazid and rifamycin
How to distinguish between TB strains 1) 2) 3) 4)
1) Drug resistance
2) Spoligotyping
3) Variable number of tandem repeats (mirutyping)
4) Whole-genome sequencing
Highest-resolution technique to distinguish between TB strains
Whole-genome sequencing
What is spoligotyping?
Compare mutatable parts of different TB genomes
What is variable number of tandem repeats?
Compare parts of TB genomes that have tandem repeats. Compare number. Often compare 24 parts of genome.
Beijing strain
1)
2)
3)
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
Demographic versus personal risk of TB
1)
2)
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
Case of TB outbreak in British Columbia
1)
2)
3)
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
Why would a 100% vaccine given to 100% of the population not eliminate TB?
There are still cases of latent TB that can progress to active TB
