1. What’s New in STI Testing?
Dr Vendela McNamara
LLR Sexual Health Service

2. Learning Objectives
Overview of basic principles of PCR and its application to STI testing
Understand which anatomical sites are most suitable for STI sampling
Gain insight into importance of testing in relation to antibiotic resistance

4. Chlamydia Historically: Culture, DIF, ELISA PCR Highly sensitive
Suitable for self-taken samples
Can be combined with other tests (Gonorrhoea)
BUT
Potential for contamination
May miss genetic variants
Does not give information on antibiotic sensitivities

5. PCR (Polymerase Chain Reaction)

6. Chlamydia: Which Sites?
MSM
Urine, throat, rectal
Positive rectal Chlamydia- supplementary testing for LGV serovars
Pooled Sampling of pharyngeal/urethral/rectal samples (Sultan et al, J Clin Microbiol, March 2016)

7. Chlamydia: Which Sites?
Women
Vulvo-vaginal sample (VVS): Sensitivity 96-98% (superior to urine and to cervix)
Heterosexual Men
First Catch Urine (FCU)

8. Throat/Anorectal Sampling in Women?
Current BASHH guidance: consider anal swabs where there is a history of RAI
Gratrix et al, Clin Inf Diseases November 2014
3055 Canadian women screened for rectal Chlamydia (CT) regardless of history of AI
Prevalence of rectal CT 13.5%
133 cases of rectal only CT, ie: case detection rate increased from 300 to 433 (44.3%)
No association between rectal Chlamydia and history of AI

9. Throat/Anal Sampling in Women?
Koedijk et al Int J STD AIDS Sept 2012
National suveillance data from Dutch STI clinics , n=207,134
Overall CT pos 10.2%, GC 1.2%
427 isolated anorectal CT, 194 isolated pharyngeal infections, ie: 13% cases would have been missed if genital sampling only
115 isolated anorectal GC, 275 isolated pharyngeal infections, ie: 30% cases would have been missed if genital sampling only

11. Gonorrhoea PCR highly sensitive
Combined Chlamydia urine/rectal/throat samples for men
Combined vulvo-vaginal/rectal/throat samples for women
Microscopy: valuable as point of care testing
Culture still essential for antibiotic sensitivities

12. Gonorrhoea: Microscopy

13. Syphilis

14. Syphilis Serology Lesional testing VDRL replaced by RPR
EIA, TPPA usually positive within 1-3/12
Lesional testing
New data to suggest primary lesions may vary from classic single, painless chancre
Essential for early diagnosis before serology becomes positive
PCR
Dark ground microscopy

15. HIV Testing Fourth Generation testing for both antigen and antibody
1 month window period

16. Trichomonas Vaginalis

17. Trichomonas Sites for testing
Women: Posterior fornix, Self-taken, ?Urine
Men: Urine, urethra, preputial sac
Direct microscopy: Sensitivity as low as 40-60%
Rapid POC Tests, Genzyme Diagnostics: Sensitivity 80-95%
Culture- “gold standard” up until recently
PCR: Sensitivity 97%, Specificity 99% (Aptima TV, Genprobe)

18. Mycoplasma Genitalium
Proven role in NSU (15-30%), probable role in cervicitis/PID, ?proctitis
Difficult to culture
PCR testing recently available, includes detection of Macrolide resistance

19. Dean Street Express, Soho

21. Summary
PCR offers highly sensitive testing at multiple anatomical sites
Self taken swabs possible for asymptomatic patients
In age of emerging antibiotic resistance, surveillance of resistance patterns essential