Gonorrhea guide: Screening and diagnostic testing

On this page

• Screening
• Diagnostic Testing
  • Nucleic acid amplification test (NAAT)
  • Culture
  • Gram stain
  • Recommended specimens and tests for N. gonorrhoeae
• References

Screening

Screening for N. gonorrhoeae is recommended for anyone presenting with risk factors for Sexually transmitted infection (STI). Screening is effective for detecting and treating asymptomatic infections as well as preventing complications, transmission and reinfection. Depending on the type of sexual activity, it may be necessary to collect specimens from multiple anatomical sites.

Adolescents and young adults

Screen sexually active people under 25.

Pregnant people

Screen all pregnant people during their first trimester or at their first antenatal visit, and again in their third trimester.

Screen pregnant people at the time of labour in any of the following situations:

• No prenatal screening has occurred (no valid results available at the time of labour).
• Third trimester screening has not occurred.
• A positive test result was obtained for NG or CT during pregnancy without appropriate follow-up, including treatment and a test-of-cure.^{Footnote 1}

Neonates

• Screen neonates exposed to gonorrhea

Other Sexually transmitted and blood-borne infections (STBBIs)

STBBI screening recommendations vary by age, gender/sex, medical and sexual history. Any person with STBBI risk factors should be screened for STBBIs and treated appropriately to prevent transmission and reinfection.

People with N. gonorrhoeae often have a co-infection with C. trachomatis^{Footnote 2Footnote 3Footnote 4}.

Gonorrhea can increase the risk of HIV acquisition and transmission^{Footnote 5Footnote 6Footnote 7}.

People being evaluated or treated for a gonorrhea infection should be screened for:

• Chlamydia
• Syphilis
• HIV, as per the recommendations in the HIV Screening and Testing Guide

Diagnostic testing

Clinical presentation and sexual history determine which specimens should be collected and the type of test to use. Laboratory tests for the diagnosis of gonorrhea may include culture, NAAT and microscopy (Gram stain).

Note:

• The sensitivity and specificity of these tests varies widely.
• Consult your local laboratory for available tests, specimen collection and test performance.

Nucleic acid amplification tests (NAATs)

NAATs are the most sensitive tests for N. gonorrhoeae^{Footnote 8Footnote 9} and may increase the number of cases diagnosed^{Footnote 9Footnote 10}.

NAAT may be done without waiting 48 hours post-exposure. This is based on expert opinion that NAAT can detect small amounts of DNA or RNA (inoculum).

Validated NAAT can be used to detect rectal and pharyngeal infections.

Some NAATs may generate false positive results due to possible cross-reaction with other Neisseria species. If a false positive result is suspected, consult with your laboratory for further guidance.

Culture

Culture provides antimicrobial susceptibilities and should be used when antibiotic resistance is suspected. Culture provides important case management information and is critical for improved public health monitoring of AMR patterns and trends^{Footnote 11Footnote 12Footnote 13Footnote 14Footnote 15Footnote 16}.

•  Successful culture requires proper collection and transportation of appropriate specimens, or immediate inoculation of medium^{Footnote 17Footnote 18}.
• Cultures obtained less than 48 hours after exposure may give false negative results

Since NAATs are more sensitive than culture, consider collecting specimens for both culture and NAAT where feasible.

• Consult with your local laboratory for guidance

Culture is strongly recommended (together with NAAT) in the following situations:

• As a TOC for suspected treatment failure
• If the infection was acquired in countries or areas with high rates of AMR. Ceftriaxone-resistant strains^{Footnote 19Footnote 20} have been reported in Canada, Japan and Australia, all associated with travel to South-East Asia.

Culture is also recommended (together with NAAT) in the following situations:

• Symptomatic patients
• PID
• Pregnant people
• Sexual abuse/sexual assault (rectal, pharyngeal, vaginal)^{Footnote *}

Gram stain

The presence of Gram-negative intracellular diplococci (GNID) seen on direct microscopic examination of urethral smears is highly predictive of N. gonorrhoeae in symptomatic men^{Footnote 18}.

The sensitivity and specificity of the Gram stain depends on the type of specimen^{Footnote 18}.

• Urethral specimens from symptomatic males have a sensitivity and specificity of 95%, but are less sensitive in asymptomatic males (50-75%)^{Footnote 21}.
• Endocervical specimens from adult females are not routinely recommended as the sensitivity is 45–65% and the specificity is 90%.
• Gram stain is not suitable for pharyngeal and rectal specimens.

Recommended specimens and tests for N. gonorrhoeae

Specimens and tests for urogenital sites (urethral, endocervical, vaginal)

Asymptomatic people:

NAAT is the screening test of choice.

Test	Specimens for asymptomatic malesFootnote 10	Specimens for asymptomatic females
NAAT	First-void urine or Urethral swab	Vaginal swab, self-obtained or collected by a clinician or Cervical swab or First-void urine

Note

Urine specimens should be first-void urine (initial 10 to 20 mL of the urine stream). Ideally, the person should not have voided for at least two hours prior to urine or urethral swab specimen collection. More recent voiding does not preclude testing.^{Footnote 22}

Males:

• First-void urine also called first-catch urine (FCU) is preferred over a urethral swab for NAAT

Females:

• NAAT for N. gonorrhoeae using vaginal swabs may identify more infections in females than cervical swabs, urethral swabs or urine^{Footnote 23}.
• Self-collected vaginal swabs are more acceptable to females than provider-collected vaginal swabs
• Acceptability of urine testing is high, making urine-based NAAT ideal for screening females.

Symptomatic people

Physical examination is essential when an STI is suspected. Collect specimens based on clinical presentation and sexual history, prior to treatment.

Due to high rates of concomitant infection, specimens should be collected for the diagnosis of both gonococcal and chlamydia infections by NAAT; and for culture, if available, for the diagnosis of gonococcal infection^{Footnote 3Footnote 10}. NAAT can detect both C. trachomatis and N. gonorrhoeae from a single specimen.

Symptomatic males:

• Obtain a urethral swab for Gram stain and culture if available.
  • It is preferable that the person not have voided for at least 2 hours prior to specimen collection; however, this is not mandatory^{Footnote 24Footnote 25}.
  • The presence of GNID seen on direct microscopic examination of Gram stain smears is highly predictive of N. gonorrhoeae^{Footnote 18}
  • Urethral specimens from symptomatic males have a sensitivity and specificity of 95%
• Obtain urethral specimens for NAAT (urethral swab or first-void urine)  

Symptomatic females:

• Obtain cervical swabs for NAAT and for culture, if available
  • NAAT may be the only available testing method in some laboratories
  • Cultures obtained less than 48 hours after exposure may give false negative results
  • Vaginal swabs (may be self-collected) or urine can also be used for NAAT.
  • Vaginal swabs may be collected without speculum exam
• Check whether your local laboratory accepts self-collected vaginal swabs.

Specimens and tests for extragenital sites (pharyngeal and rectal)

Asymptomatic and symptomatic

Consider collecting specimens for both culture and NAAT

• Check with local laboratory about the availability of NAAT for validating NAAT for extra-genital specimens. If NAAT is unavailable, test by culture.  

Pharyngeal specimens are recommended for:

• All females with a history of performing oral sex
• All males with a history of performing oral sex who are at high risk of exposure (gbMSM, multiple sexual partners or sex with a partner who is at high risk of infection) 

Rectal specimens are recommended for:

• People with a history of receptive anal intercourse, regardless of history of condom use
• People with rectal symptoms^{Footnote 26}

Consider rectal screening in all gbMSM regardless of history of receptive anal intercourse (RAI)^{Footnote 27Footnote 28Footnote 29}.

References