Laboratory diagnosis of Sexually Transmitted Infections

 

Learning objectives:

1.     Classification of different STIs & agents causing them.

2.     Sample collection & transport methods

3.     Microscopic methods

4.     Culture methods

5.     Serological tests

6.     Molecular methods

 

·        The sexually transmitted infections are a group of communicable diseases which are transmitted by sexual contact.

Classification: Into two groups (1) Infections with local manifestations & (2) Infections with only systemic manifestations

1.     Infections with local manifestations

·        Genital ulcers

·        Urethral discharge

·        Vaginal discharge

·        Genital warts

·        Pelvic inflammatory diseases.

 

Agents causing local manifestations:

v  Genital Ulcer:

·        Syphilis: by Treponema palladium

·        Herpes genitalis:Herpes simplex virus type 2 & 1

·        Chancroid: by Haemophilusducreyi

·        Lymphogranulomavenereum: by Chlamydia trachomatis

·        Donovanosis: by Klebsiellagranulomatis

 

Comparison genital ulcer:

Disease	Genital ulcer	Lymphadenopathy
Syphilis	Painless, indurated single	Painless, moderate swelling (no bubo)
Herpes	Multiple,painful	Absence or moderate swelling (no bubo)
Chancroid	Painful, soft single or multiple	Painful, soft, marked swelling leads to bubo
LGV	Painless	Painful and soft
Donovanosis	Painless beefy red ulcer	Absent (pseudo bubo may be present due to subcutaneous swelling)

 

v  Urethral discharge:

§  Gonorrhea: Neisseria gonorrhoeae

§  Non gonococcal Urethritis(NGU)

§  Chlamydia trachomatis(D-K)

§  Mycoplasma genitalium

§  Herpes simplex virus

§  Candida albicans

§  Mycoplasma homonis

§  Trichomonasvaginalis

v  Vaginal Discharge:

§  Vulvo vaginal candidiasis: Candida albicans and non albicans spp.

§  Bacterial vaginosis:Gardnerellavaginalis, Mobiluncus species

§  Trichomonas vaginitis: Trichomonasvaginalis

v  Genital warts:

§  Condylomaacuminate:Human papilloma virus

v  Pelvic inflammatory disease(PID):

§  Neisseria gonorrhoeae

§  Chlamydia trachomatis

 

2.      Agents transmitted by sexual route, producing only systemic manifestations and do not cause local manifestations are: HIV, HBV, HCV

 

 

Laboratory Diagnosis

v Specimen Collection

·        Discharge from the infected area - vaginal or urethral discharge in a sterile container

·        Sterile swabs (if the discharge scanty): Charcoal impregnated swabsforgonococcal infection

·        Fluid from the vesicles:genital herpes

·        Blood in plain tube: serological test e.g. syphilis

v  Transport:

·        Immediately: Most of organisms are delicate not viable for long outside body

·        Transport medium: Modified Stuart ‘s medium

v Microscopy:

·        Wet mount examination: vaginal discharge

-        Trichomoniasis: Pus cells along with motile trophozoites

-        Candidiasis:  budding yeast cells along with pseudo hyphae

·        Gram-stained smear:

•        Bacterial vaginosis—clue cells (vaginal epithelial cells studded with gram variable pleomorphic coccobacilli) :Gardnerellavaginalis

•        Gonorrhea—intracellular kidney-shaped gram-negative diplococci

•        Candidiasis—gram-positive budding yeast cells along with pseudo hyphae

·        Giemsa stain:

•        Klebsiellagranulomatis - Donovan’s bodies( macrophages filled with bipolar stained bacilli)

•        Chlamydia trachomatis - inclusion bodies

·        Dark field microscopy and silver impregnation –

•         syphilis - spirally coiled bacilli

 

v Culture

Specimens are inoculated onto the appropriate culture media/cell line:

•        Thayer-Martin medium—for N. gonorrhoeae

•        Chocolate agar added with isovitalex and vancomycin— for H. ducreyi

•        McCoy cell line—for Chlamydia trachomatis

•        Sabouraud’s dextrose agar (SDA)—for Candida species

•        Vero cells, monkey kidney cell line - herpes simplex virus.

 

v Serology:

•        VDRL or RPR test, TPHA, TPI -syphilis

•        CFT-chlamydia infection

 

v Molecular Test

•        Multiplex PCR and real-time PCR:For simultaneous detection of pathogens suchas: C.trachomatis,Gonococcus, T. pallidum and H. ducreyi andHSV.