STI and HIV aetiology and public health burden

Question 1

What is the basic reproductive rate

Answer 1

the number of secondary cases of an infection that arise from a primary case at t=0

Question 2

what does the Ro have to be for a disease to be an epidemic

Answer 2

Ro=2

Question 3

what does the Ro have to be for a disease to disappear

Answer 3

Ro=0.5

Question 4

what are the three factors that make up the formula for the basic reproductive rate

Answer 4

• transmission probability per sexual partner (b)
• duration of infection (d)
• rate of partner change (c)

Question 5

what is the formula for the effective reproductive rate

Answer 5

BcD(x)

x = the proportion of the population that is susceptible

Question 6

what types of things influences the transmission probability per sexual partner of a disease

Answer 6

condom usage
types of sex
duration of sex
bleeding associated with sex
another STI present
HIV present
load of organisms
duration of partnership

Question 7

what types of things influences the duration of the infection of an STI

Answer 7

• treatment and clinical services
  screening
• symptom recognition
• asymptomatic infection

Question 8

what types of things influences the rate of partner change

Answer 8

education
behavioural interventions
mixing patterns
concurrency
core and non core groups

Question 9

what is the “core group”?

Answer 9

the small population of people within the larger population that have a higher risk of infection compared to the overall population
(the SD of the mean)

Question 10

what is assortative and disassortative mixing

Answer 10

assortative - mixing between two high risk people

dissassortative - mixing between one high risk and one low risk person

Question 11

what is concurrency

Answer 11

those people who have more than one sexual partner at a time

Question 12

how do we account for the core group

Answer 12

rate of partner change (c) = mean partners + (SD)2/mean

Question 13

what is the theory behind why gonorrhoea rates went up in the last part of the 20th century

Answer 13

because fear campaigns we so strong that non risk gay men stopped having sex and only those having lots of partners continued to have sex with those who also had lots of partners: assortative mixing

Question 14

what is the dominant determinant of the prevalence of an STI

Answer 14

the duration of infection (D)

Question 15

what is PreP

Answer 15

pre-exposure prophylaxis (people who are HIV negative will take medication to prevent risk of HIV)

Question 16

what is PEP

Answer 16

post exposure prophylaxis

within 72 hours of someone who may have been exposed to HIV - treatment lasts 4 weeks

Question 17

what is the most effective way of preventing HIV transmission

Answer 17

HIV treatment with antiretrovirals to lower the viral load

Question 18

why is it so important to treat HIV in its primary stages

Answer 18

because the acute HIV is much more transmissible (much higher viral load)

Question 19

what are the symptoms of primary HIV infection

Answer 19

sore throat
fever
rash

Question 20

where would rapid HIV testing be useful

Answer 20

• poor access
• cost, geographical
• fear
• poor health service structure

Question 21

which STI in particular is associated with an increased transmission of HIV

Answer 21

genital ulcer disease - HSV