Lecture 12. Public Health 3: Sexually Transmitted Infections (STI) Flashcards
How many diagnosed cases of STIs were there in England in 2019?
466,742
What is the current STI causing the most concern?
Chlamydia (45-50% of total cases)
When was vaccination against HPV introduced?
2008
What disease was virtually eliminated in the UK through antibiotic use but has seen a resurgence in gay men?
Syphilis (8010 cases in 2019 with 7189 of those being men)
Where are STIs diagnosed?
Genitourinary medicine (GUM) clinics
How is prevalence calculated?
Incidence x duration
What was the prevalence of chlamydia in females aged 16-24 in 2010-2012?
~3.2%
Of those with chlamydia, what percentage are asymptomatic?
70% women
50% men
What are the two aims of the National Chlamydia screening program?
Surveillance data (incidence in those people who report and are accurately diagnosed)
Treatment of infected individuals = control
What is the relationship between genital chlamydial infection, pelvic inflammatory disease (PID) and the sequelae of PID?
10-40% of untreated genital chlamydial infections result in PID
PID can result in infertility (in ~20% of cases) and ectopic pregnancy (in ~47%)
What are the risk factors of STIs?
STI have a lower limit to the “intimacy” of contact required for transmission (‘flu can be transmitted via sexual contact)
Risk of acquiring STI is almost exclusively determined by the rate of sexual partner change (Not necessary by the number of sexual contacts within a partnership)
Choice of partners (Men are ~4yrs older than their female partners, IQ of non-casual sexual partners is highly correlated)
What age groups are the biggest risk of getting an STI in males and females?
Male: 25-34 (4.7%)
Female: 16-24 (6.7%)
How can sexual behaviour be measured up to 1985 and why was this stopped?
Interview/questionnaire
Up to 1985 all were biased, and concentrated on attitudes & motivations
What must be accounted for when measuring sexual behaviour through random, large-scale surveys?
They are subject to non-disclosure
Definitions of sexual acts are not commonly agreed (e.g in all studies the number of partners claimed by men exceeds those claimed by women)
What is NATSAL?
The National Survey of Sexual Attitudes and Lifestyles
Rolled out every 10 years (started in the 90s)
What data is shown from NATSAL 3 (2010-12)?
Average age of first intercourse had decreased, but average age of first child had increased
The number of people having large numbers of sexual partners over a five year time span has increased
Why do reported results ≠ actual results?
Self-report is a poor predictor of recent sexual behaviour
(e.g large number of 16 year olds claim large amount of sexual patterns or women having PSA when claiming they didn’t have sex)
What are prostate-specific antigen (PSA levels)?
Measure of exposure to semen in the past 2 days
What is the distribution of sexual activity within the UK?
Most people have no/few partners, few have very many (about 20% of people have 80% of sexual partnerships)
Which is higher in the distribution sexual activity, variance (v) or mean (m)?
v > > m
What is the average variance and mean number of sexual partners of homosexuals within the UK?
v ≈ 5 per year
m ≈ 1 per year
What is R₀ proportional to?
(m² + v)/m = (m + v/m)
What is the core group?
10+ sexual partners
Small proportion have disproportionate effect on epidemic
Basic reproduction number should include the variability in behaviour
Most likely to become infected and most likely to infect
What is an assortative sexual behaviour?
People with many sexual partners are more likely to have partners who have many sexual partners
What is a random sexual behaviour?
People have sexual partners at random
What is a disassortative sexual behaviour?
People with many sexual partners have partners who have few sexual partners
What sexual behaviour increases R₀?
Assortative
What is concurrency?
Sexual partnerships in parallel bigger risk than sexual partnerships in series
What does human papillomavirus (HPV) cause?
Genital warts and cervical, anal, penile & oropharyngeal cancers
Is the HPV vaccine against all types of HPV?
No, only some
Why did did the UK switch from the bivalent Cervarix to Garadasil HPV vaccine?
Garadasil protects against the four main types of HPV (6, 11, 16 and 18) and is more cost-effective
If all females are successfully vaccinated against HPV, do males need to get a HPV vaccine?
If all females were successfully vaccinated, then heterosexual males would not contract HPV. However given that the benefits of the programme would be seen over an extended period of time, it agreed to apply a different rate to assessing the vaccine which meant that a gender neutral programme was deemed to be cost-effective.
