Lecture 27; Sexual behaviours

Question 1

Describe the factors to consider when it comes to transmission of STIs?

Answer 1

Modes of transmission // how plausible? i.e HIV has a narrow range of transmission

How probable per an act? i.e HIV = 1.4% per anal intercourse

How probable per relationship? HIV 6% chance of transmission in a year

Question 2

What drives incidence of STI transmission?

Answer 2

Prevelence drives incidence

i.e If not STIs are around then there isnt going to be incidence!

Question 3

What are considerations of partnership level transmission in STI?

Answer 3

• Treatments i.e Prep
• Condom use.
• Circumcision
• Type of contact
• STI co-factors
• Viral load in body compartments
• Stage of infection
• Subtype of STI

Question 4

At population rate what is Ro?

Answer 4

R0 = Average number of secondary cases generated by each infected person

Question 5

What determines R0 for STIs?

Answer 5

• Probability of transmission i.e Stage of infection, viral load, condom use, prep
• Structure of sexual contacts i.e Numbers, nature, timings etc etc
• Duration of infectiousness i.e testing, treatment, adherence

Question 6

How does sexual networks change risk?

Answer 6

Network placement changes your risk, not the number of partners you have.

• Greater or lesser outbreak potential depending on your and your contacts backgrounds etc.

= Superspreaders
= Reservoirs
= Proximity to infected

Question 7

What can change outbreaks?

Answer 7

Contact tracing
Condom use
Prep
Testing and treatment