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NCID > For Healthcare Professionals > Diseases and Conditions > Sexually-Transmitted Infections

Sexually-Transmitted Infections

Sexually-Transmitted Infections

Causative Agents

In 2009, the top 5 sexually-transmitted infections (STIs) diagnosed in Singapore were: Chlamydia trachomatis (infection of the urethra, cervix, pharynx and rectum), Neisseria gonorrhoeae (infection of the urethra, cervix, pharynx and rectum), non- gonococcal urethritis (NGU), herpes simplex virus (HSV): types 1 and 2 (ano- genital herpes), and human papilloma virus (HPV) (ano-genital warts). Other important STIs are Treponema pallidum (syphilis), Trichomonas vaginalis (trichomoniasis), and human immunodeficiency virus infection (HIV).

Incubation Period

Chlamydia : 5 - 14 days
Gonorrhoea : 3 - 5 days
Ano-genital herpes : 2 - 14 days
Ano-genital warts :1- 6 months (mean 3 months)
Syphilis : 10 - 90 days (mean 21 days)
Trichomoniasis : a few days
HIV : mean of 1 month to acute HIV infection, mean of 5 to 8 years to AIDS if untreated

Infectious Period

Gonorrhoea, chlamydia : active infection, symptomatic or asymptomatic Ano-genital herpes : presence of vesicles and erosions; asymptomatic
viral shedding is also an important route of transmission
Ano-genital warts : higher with presence of active lesions;
subclinical infections common
Syphilis : during primary and secondary stages
Trichomoniasis : active infection, symptomatic or asymptomatic
HIV infection : infectious from early on till demise if untreated

STI may present with:

  • genital discharges (gonorrhoea, chlamydia, trichomoniasis)
  • ano-genital ulcers (herpes, syphilis)
  • ano-genital growths (warts, molluscum contagiosum)
  • rashes (syphilis, scabies)
  • pelvic inflammatory disease (gonorrhoea, chlamydia)
  • epididymo-orchitis (gonorrhoea, chlamydia)
  • HIV infection may present in several ways depending on the organ systems affected (see chapter on HIV).

Many STIs may be asymptomatic and can be detected only if the appropriate laboratory screening tests are performed (see references).

  • Ano-genital Herpes (First episode/ Recurrent)
    • Typical vesicles or erosions in the ano-genital area  (may be severe with  initial episode).
    • Confirmed by viral isolation, direct immunofluorescence (DIF), PCR, EIA   or type-specific serological test against glycoprotein gG1 (HSV-1) & gG2 (HSV-2) for HSV (serology is not useful for first episode infection as it takes between 6 and 8 weeks for serological detection following a first episode).
  • Chlamydia Genital Infection—(A laboratory diagnosed infectious disease)
    • Nucleic acid amplification test (NAAT) (e.g. PCR) positive for C.  trachomatis from ano-genital specimen or urine; or
    • Antigen detection (e.g. EIA, IF) positive for C.  trachomatis  from  ano- genital specimen.
    • Chlamydia serology is not useful as it does not distinguish between past or current infection; there is also cross-reactivity with other chlamydial species.
  • Gonorrhoea
    • Purulent genital discharge (associated with dysuria in males), history of  recent unprotected sexual intercourse; or
    • Gram-stained smear from genital discharges  with  Gram-negative intracellular diplococci; or
    • Positive culture on selective media for N. gonorrhoeae; or
    • Urine nucleic acid amplification test (NAAT) (e.g. PCR) positive for N. gonorrhoeae.
    • Gonorrhoea serology is not useful due to lack of sensitivity & specificity.
  • Non-Gonococcal Urethritis (NGU)
    • Mucopurulent or whitish discharge from urethra associated with dysuria or urethral discomfort/itch in males, history of recent unprotected sexual intercourse; or
    • Gram-stained smear showing increased pus cell count (5 or more WBC per high-power field) in absence of Gram-negative intracellular diplococci; or
    • Visible threads in the first glass of a 2 glass urine test.
  • Infectious Syphilis
    • Presence of primary chancre usually solitary, indurated, non-tender (but the ulcer may also be atypical), inguinal lymphadenopathy;
    • Presence of clinical features of secondary syphilis e.g. rash especially on palms and soles, ano-genital patches and growths, generalized lymphadenopathy, patchy hair loss; confirmed by:
      • Positive dark-field microscopic examination of exudate from primary or secondary ano-genital lesions for spirochaetes; or
      • Reactive blood tests for syphilis:
        • Non-specific treponemal tests (RPR/VDRL)
        • Specific treponemal tests (TPPA/TPHA, LIA, Syphilis EIA)
  • Non-Infectious Syphilis
    • Presence of clinical features of tertiary syphilis (viz. cardiovascular syphilis, central nervous system syphilis); or
    • Asymptomatic infection with reactive blood tests for syphilis
    • Note - persistence of reactive serology in patients with treated syphilis may be indicative of a serological scar
  • Trichomoniasis
    • Diagnosed by direct wet-mount microscopy and culture. Serology is not useful.
  • Mycoplasma: There are no clear guidelines for screening with serology.
  • Candida: Serology is not useful as it is not indicative of a genital cause/disease.

  • All patients with a STI should be screened for syphilis, hepatitis B and HIV infection.
  • Patients should receive recommended antimicrobials in the correct dosages (see references). Test-of-cure is important to assess treatment efficacy particularly for gonorrhoea and syphilis.
  • Chlamydia:
    • Doxycycline 100mg bid x 7days (avoid if pregnant)
    • Erythromycin 500mg qid x 7 days
    • Erythromycin ethylsuccinate 800 mg qid x 7days
    • Azithromycin 1gm x 1 dose (useful if adherence is an anticipated problem)
  • Gonorrhoea:
    • All patients with gonorrhoea should be given concurrent treatment for chlamydia.
    • Fluoroquinolones are not recommended due to high prevalence (80%) of resistance in N. gonorrhoeae.
    • Repeat smears and cultures should be performed on or around the 14th post-treatment day.
    • For those with penicillin allergy, IM spectinomycin can  be  used.  Or  consider allergy testing and desensitization. Specialist consultation recommended.
    • Uncomplicated (pharynx/urethra/rectum/cervix):
      • IM Ceftriaxone 250mg x 1 dose; or
      • Cefixime 400mg x 1 dose
    • Severe or Disseminated Gonococcal Infections (DGI):
      • IV Ceftriaxone 1-2g daily. Duration depending on site of infection and response
  • Syphilis:
    • Cases of syphilis should be treated with intramuscular benzathine penicillin. They should have serological tests repeated at 3 months, and then every 6 months for 2 years. Suspected cases of neurosyphilis should have a lumbar puncture performed.
    • For late latent syphilis, syphilis of unknown duration, congenital syphilis, neurosyphilis or syphilis in pregnancy, the treatment recommendations are different and relevant expert advice should be sought.
    • Primary and Secondary Syphilis:
        • IM Benzathine Penicillin G 2.4 million units x 1 dose. (Some authorities use 2 doses for secondary syphilis); or
        • IM Aqueous Procaine Penicillin G 600,000 units daily x 10 days
    • Penicillin allergic patients:
        • Doxycycline 100mg bid x 14 days; or
        • Erythromycin 500mg qid x 14 days; or
        • Azithromycin 500mg daily x 10 days
  • Cases of first-episode genital herpes should be treated with acyclovir or related medications. Recurrent genital herpes may be treated with either episodic or suppressive anti-viral regimens (see references).
  • Ano-genital warts can be treated medically or surgically; they  should  be followed up till all visible warts are cleared. Regular PAP smears are recommended for female patients.
  • Cases of trichomoniasis are treated with metronidazole (see references).

  • Chlamydia, gonorrhoea, syphilis (infectious, non-infectious and congenital), NGU, genital herpes (first episode and recurrent) should be notified to the DSC clinic by fax (62994335) using form MD 131 or electronically via CD-LENS.
  • Provide information on type of HSV detected where available.
  • Repeat notifications of recurrent genital herpes are not necessary.
  • The name, NRIC, address and telephone number need not be completed, but initials, sex, date of birth, ethnicity and residential status should be provided.

  • Patients with STI should be given information about their current infection.
  • To prevent future infections, information on safer sex should be given too e.g. correct and consistent condom use.
  • Partner management/contact tracing should be conducted to diagnose and treat infections in sex partners, to prevent complications and further transmission.
  • Antenatal mothers should be routinely screened  for syphilis,  hepatitis B and  HIV infection.
  • Hepatitis B vaccination should be given to those who are negative for HBV markers.
  • Brothel-based sex workers are provided with STI/HIV educational information and taught negotiation skills to achieve 100% condom use; they are screened routinely for syphilis, gonorrhoea, chlamydia, HIV and hepatitis B infections. Targeted STI/HIV education for at risk groups e.g. youth, MSM, military personnel, and clients of sex workers should be conducted regularly.
  • Patients are encouraged to seek early treatment, not to self-medicate and to complete all prescribed medications.
  • Self-medication with antibiotics may result in the emergence of drug-resistant strains. Medical practitioners should not dispense antibiotic chemoprophylaxis as there is no one universally effective antibiotic, this may also result in a false sense of security and may be dangerous.


  1. DSC clinic website: Accessed Dec 2010.
  2. STI Management Guidelines - Department of STI Control, National Skin Centre, 2007
  3. MOH Clinical Practice Guidelines on genital ulcers & discharges, May 2009: Accessed Dec 2010.

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