Aetiology and Risk Factors - STIs Flashcards
Why is gonorrhoea more common in Indigenous populations?
because of less access to testing and treatment which means the period of infectivity is months compared to days for people in urban areas
What is the basic reproductive rate (Ro)?
the number of secondary cases that arise from a primary case at t=0
What is an epidemic?
where one primary case leads to two secondary cases
What happens when Ro>1?
Initially all infected people come in to contact with susceptible people but as the disease spreads it will reach a steady state where new cases equals cured cases
What happens when Ro<1?
eventually the disease will die out
What does basic reproductive rate (Ro) depend on?
transmission probability per partnership, duration of infection and rate of partner change
What is the effective reproductive rate (Rt)?
the basic reproductive rate multiplied by the proportion susceptible, Rt = Ro x X
What determines the transmission probability per partnership?
condom usage, type of sex, duration of sex, bleeding associated with sex, presence of other STIs (HIV), viral load
Why is more difficult to control a viral STI than a bacterial STI?
the duration of infection for a viral STI is longer
How can transmission probability per partnership be reduced for HIV?
decrease cofactor STIs (gonorrheoa and chlamydia), decrease viral load with treatment, increase condom use (education and availability), change type of sex
What is PEP?
post exposure prophylaxs - an antiretroviral therapy taken for a month after exposure to possible HIV
Why did syphilis increase during WWII?
increased number of partners
Why did syphilis increase in the 1960s?
sexual revolution, less condom usage, more men having sex with men, contraceptive pill
Why did syphilis increase in the 2000s?
less condom usage, more unsafe sex, more partners among men who have sex with men
What is the non core group?
most people who have few partners - acts like the mean for the rate of partner change
What is the core group?
few people who have many partners - acts like the standard deviation for rate of partner change
What is assortative mixing?
high risk with high risk (core group with core group)
What is disassortative mixing?
high risk with low risk
What is concurrency of partners?
defined as a sexual partnership when one or more of the partnership members have other sexual partners while continuing sexual activity with original partner
Why is there no benefit in an STI intervention that is aimed at the non core group?
because even if the mean is reduced it wont reduce the standard deviation, also it may increase rates in the core group because it will increase the assortative mixing (core with core) and thus wont control STI transmission
Why is the HPV vaccine effective?
because it reduces the population that is suscpetible so will reduce the effective reproductive rate
