L19 - Sexually transmitted infections Flashcards
STI full name
Sexually transmitted infection
Recent Issues in STI in Hong Kong
- Resurgence of syphilis
- Gonorrhoea: Increase in plasmid and chromosomal mediated resistance
- Chlamydia trachomatis: remain a difficult infection to confirm
- Human papillovirus: associated with genital malignancies
- HIV: clusters of same sex transmission
Definition of STI
diseases that are transmitted by sexual contact
STI that may be transmitted via non-sexual routes
HIV, syphilis also transmitted by blood transfusion or needle stick injury.
What is unique about STI
1) Transmitted by sexual contact
2) Some (e.g. HIV, syphilis) may be transmitted by blood transfusion or needle stick injury
3) STI do not ‘travel alone’
4) Many STIs are asymptomatic
5) The nature of infection acquisition (sexual) interferes with necessary history taking and counselling, especially when not performed in an non-judgemental fashion
Euphemism of prostitute
Commercial sex workers
CSW full name
Commercial sex workers
Euphemism of STI clinics
Social Hygiene Clinics
Which department are social hygiene clinics under in Hong Kong?
Department of Health
Which groups (by occupation) constitute the most in social hygiene clinic attendees?
Service worker and shop sales workers; Housewives; Unemployed; Elementary occupations
Factors affecting the rate of movement of an STI through the population
1) Efficiency of transmission
2) The rate of new sex partner acquisition and partner’s sexual history
3) The duration of infectiousness
Encounter of STI pathogens/agents
Practically never found free in the environment (not free-living) as they do not survive in the environment (as they are very sensitive to drying, disinfectant & heat)
No animal reservoir, only asymptomatic human carriers as reservoir
Therefore - cannot be environmental encounter (e.g. toilet seat or hot tub)
Why don’t STI agents survive in the environment?
As they are very sensitive to drying, disinfectant and heat
Reservoir of STI agents
Asymptomatic human carrier; no animal reservoir
Entry of STI agents
- Enter through mucous membrane (columnar epithelium) or minute abrasions in skin surface (squamous epithelium)
- Enter at local sites (vagina, cervix, urethra, rectum, or pharynx)
- Tend to cause primary lesions at or near the site of entry
General Damage and detrimental consequences of STIs
- Pelvic inflammatory disease (infertility, ectopic pregnancy).
- Anogenital cancer.
- Secondary & tertiary syphilis.
- Recurrent herpes infection.
- Increase risk of HIV infection
- Adverse outcome of pregnancy.
- Congenital diseases (e. g. syphilis, herpes)
Three most typical STI presentation
1) Urethral discharge (urethritis)
2) Genital ulcer
3) Genital lumps
Pathogen of urethral discharge/urethritis
Main Causes
1) Neisseria gonorrhoea (GC)
2) Chlamydia trachomatis
Less common
1) Ureaplasma urealyticum
2) Mycoplasma genitalium
Rare
1) Herpes Simplex virus
2) Trichomonas vaginalis (parasite)
3) Yeast
Gonococcal (GU) urethritis characteristics (Incubation, Onset, Dysuria, Discharge, Relapse)
Incubation period: 2-5 days Onset: Abrupt Dysuria: prominent Discharge: Copious Relapse: Rare
Non-gonococcal (NGU) urethritis characteristics (Incubation, Onset, Dysuria, Discharge, Relapse)
Incubation period: 7 - 14 days Onset: Gradual Dysuria: Mild Discharge: Scanty Relapse: Common
Comparison between GU and NGU urethritis
GU vs NGU Incubation period: 2 - 5 days vs 7 - 14 days Onset: Abrupt vs Gradual Dysuria: Prominent vs Mild Discharge: Copious vs Scanty Relapse: Rare vs Common
Management strategy of urethritis
1) Establish presence of urethritis - by means of Physical examination + microscopy (visualisation of WBC, bacteria)
2) Two approaches
i) Empirical treatment, no workup in initial visit (cover both GC and CT)
ii) Workup (diagnostic examination performed) and treat
3) Evaluate and treat partner(s) appropriately
4) Follow up examination (optional)
pharmacology of urethritis treatment
- Single does ceftriaxone given intramuscularly for GC + single dose azithromycin for CT
- Doxycycline for 7 days (alternatives for CT)
- In Hong Kong, tetracyclines, penicillin, fluoroquinolones, oral cephalosporins now abandoned as first line GC urethritis treatment due to common resistance
Taking specimen for Microbiology tests for GC (procedures, precautions)
Procedure:
1) Directly inoculate onto agar plate at bedside
2) Transport specimen in special transport tube/swab
3) Send to lab immediately
Precautions:
- GC dies quickly
- Good result requires meticulous techniques
- Never refrigerate specimens
- Any delay will compromise yield
Microbiology tests (cell culture) for GC (Main test, culture medium, incubation)
Main test: Culture
Culture Medium: **Must use nutritive culture media with antibiotics (to inhibit overgrowth of normal flora)
- Modified Thayer-Martin medium
- Martin-Lewis medium
Incubation: 35 degree celsius, CO2 enriched, humid atmosphere
Chlamydial infections (Classification, nature, serotypical infections)
Classification: Family Chlamydiaceae; Genus Chlamydia
Nature: Obligate intracellular parasite
Serotypes:
1) C. trachomatis
a) A, B, C - Trachoma infection
b) D to K - Cervicitis, urethritis, PID, neonatal peumonia
c) L - Lymphogranuloma venereum (LGV)
2) C. pneumonia - respiratory tract infection
3) C. psittaci - psittacosis
Taking specimens for microbiology test (cell culture) for CT (nature, precautions)
Nature: Swabs, scrapings or small tissue samples
Precautions: Must be sent in special transport medium; should be immediately refrigerated (4 degrees Celsius) for up to 24 hours if cannot be delivered to lab immediately
Tests for CT
1) Cell culture to isolate CT (e.g. McCoy cell line)
2) Direct detection of antigen in specimen (i.e. Chlamydiazyme); based on EIA or immunoflorescence principles, using Chlamydia-specific antobodies
3) Serological testing (e.g. CFT/IF) NOT useeful for diagnosis
4) Nucleic acid amplification tests (e.g. PCR)
Tests for GC
1) Bacterial culture incubation (e.g. modified Thayer-Marton medium or Martin-Lewis medium)
2) Direct antigen detection not available
3) Serological test not available
4) Nucleic acid amplification tests (e.g. PCR)
Direct antigen detection for CT and GC
– Only for CT (not available for GC). e.g. Chlamydiazyme
– Based on EIA or immunofluorescence principles, using monoclonal Chlamydia-specific antibodies
– Read result as color change or under microscopy for fluorescent staining of Chlamydia elementary bodies
– Less sensitive than culture
– False-positive results from cross reacting bacterial species
Serological tests for GC and CT
1) GC - NO serological test
2) CT – Serological testing (e.g. CFT or IF) NOT
useful for diagnosis.
3) Antibody persist after infection
4) Tests interfere by cross reacting antibodies from
other chlamydial infection (e.g. C. psittaci, C. pneumoniae)
Nucleic acid amplification test for GC a1nd CT
Several commercial tests available:
1) Polymerase chain reaction (PCR)
2) Ligase chain reaction (LCR)
3) Transcription-mediated amplification (TMA)
Advantages:
1) More sensitive (vs. culture)
2) Could be performed on non-invasive specimens (e.g. urine, vulval swab) with good results; acceptable screening risk
3) For simultaneous detection of GC & CT specific nucleic acid in a single test
Disadvantages:
COST still a concern.
Infective causes of genital ulceration
1) Syphilis
2) Herpes simplex
3) Chancroid
4) Lymphogranuloma venereum (LGV)
5) Donovanosis
