Chlamydia trachomatis and Neisseria gonorrhoeae by Nucleic Acid Amplification (GEN-PROBE)
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Chlamydia is caused by the obligate intracellular bacterium Chlamydia trachomatis and is the most prevalent sexually transmitted bacterial infection (STI) in the United States.(1,2) In 2010, 1.3 million documented cases were reported to the CDC.(2) Given that 3 out of 4 infected women and 1 out of 2 infected men will be asymptomatic initially, the actual prevalence of disease is thought to be much greater than reported.(2) The organism causes genitourinary infections in women and men and may be associated with dysuria and vaginal, urethral, or rectal discharge. In women, complications include pelvic inflammatory disease, salpingitis, and infertility. Approximately 25% to 30% of women who develop acute salpingitis become infertile.(2) Complications among men are rare, but include epididymitis and sterility. Rarely, genital chlamydial infection can cause arthritis with associated skin lesions and ocular inflammation (Reiter syndrome). Chlamydia trachomatis can be transmitted from the mother during delivery and is associated with conjunctivitis and pneumonia. Finally, Chlamydia trachomatis may cause hepatitis and pharyngitis in adult.
Once detected, the infection is easily treated by a short course of antibiotic therapy.(2) Annual Chlamydia screening is now recommended for all sexually active women age 25 years and younger, and for older women with risk factors for infection, such as a new sex partner or multiple sex partners.(2) The CDC also recommends that all pregnant women be given a screening test for chlamydia infection.(2) Repeat testing for test-of-cure is not recommended after treatment with a standard treatment regimen unless patient compliance is in question, reinfection is suspected, or the patient's symptoms persist. Repeat testing of pregnant women, 3 weeks after completion of therapy, is also recommended to ensure therapeutic cure.(2)
Gonorrhea is caused by the bacterium Neisseria gonorrhoeae. It is also a very common STI, with 301,174 cases of gonorrhea reported to CDC in 2009.(1,2) Like Chlamydia, many infections in women are asymptomatic, and the true prevalence of gonorrhea is likely much higher than reported.(1,2) The organism causes genitourinary infections in women and men and may be associated with dysuria and vaginal, urethral, or rectal discharge. Complications include pelvic inflammatory disease in women and gonococcal epididymitis and prostatitis in men. Gonococcal bacteremia, pharyngitis, and arthritis may also occur. Infection in men is typically associated with symptoms that would prompt clinical evaluation. Given the risk for asymptomatic infection in women, screening is recommended for women at increased risk of infection (eg, women with previous gonorrhea or other STI, inconsistent condom use, new or multiple sex partners, and women in certain demographic groups such as those in communities with high STI prevalence.)(2) The CDC currently recommends dual antibiotic treatment due to emerging antimicrobial resistance.(2)
Culture was previously considered to be the gold standard test for diagnosis of Chlamydia trachomatis and Neisseria gonorrhoeae infection. However, these organisms are labile in vitro, and precise specimen collection, transportation, and processing conditions are required to maintain organism viability, which is necessary for successful culturing. In comparison, nucleic acid amplification testing (NAAT) provides superior sensitivity and specificity and is now the recommended method for diagnosis in most cases.(2-5) Immunoassays and nonamplification DNA tests are also available for Chlamydia trachomatis and Neisseria gonorrhoeae detection, but these methods are significantly less sensitive and less specific than NAATs.(2-5)
Improved screening rates and increased sensitivity of NAAT testing have resulted in an increased number of accurately diagnosed cases.(2-5) Improved detection rates result from both the increased performance of the assay and the patients' easy acceptance of urine testing. Early identification of infection enables sexual partners to seek testing and/or treatment as soon as possible and reduces the risk of disease spread. Prompt treatment reduces the risk of infertility in women.
Detection of Chlamydia trachomatis or Neisseria gonorrhoeae
A positive result indicates that rRNA of Chlamydia trachomatis and/or Neisseria gonorrhoeae is present in the specimen tested and strongly supports a diagnosis of chlamydial/gonorrheal infection.
A negative result indicates that rRNA for Chlamydia trachomatis and/or Neisseria gonorrhoeae was not detected in the specimen.
The predictive value of an assay depends on the prevalence of the disease in any particular population. In settings with a high prevalence of sexually transmitted disease, positive assay results have a high likelihood of being true positives. In settings with a low prevalence of sexually transmitted disease, or in any setting in which a patient's clinical signs and symptoms or risk factors are inconsistent with gonococcal or chlamydial urogenital infection, positive results should be carefully assessed and the patient retested by other methods (eg, culture for Neisseria gonorrhoeae), if appropriate.
A negative result does not exclude the possibility of infection. If clinical indications strongly suggest gonococcal or chlamydial infection, additional specimens should be collected for testing. A result of indeterminate indicates that a new specimen should be collected.
This test has not been shown to cross react with commensal (nonpathogenic) Neisseria species present in the oropharynx.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Care must be taken to avoid cross-contamination during handling of PreservCyt solution liquid Pap specimens. If testing PreservCyt specimens processed with the ThinPrep 2000 processor, it is important to follow procedures to reduce the risk for cross-contamination during Pap processing such as bleaching of the PreservCyt filter cap and changing gloves between each sample. Refer to the ThinPrep 2000 Processor Operator's Manual and the APTIMA Specimen for further guidance.
The performance of endocervical, vaginal, and male urethral swab specimens, male and female urine specimens, and PreservCyt solution liquid Pap specimens has not been evaluated in adolescents less than 16 years of age. This report is intended for use in clinical monitoring or management of patients; it is not intended for use in medico-legal applications. The performance of vaginal swab specimens has not been evaluated in pregnant women.
Appropriate specimen collection and handling is necessary for optimal assay performance.
Results should be interpreted in conjunction with other laboratory and clinical information.
A negative test result does not exclude the possibility of infection. Improper specimen collection, concurrent antibiotic therapy, presence of inhibitors, or low numbers of organisms in the specimen (ie, below the sensitivity of the test) may cause false-negative test results.
In low-prevalence populations, positive results must be interpreted carefully as false-positive results may occur more frequently than true-positive results in this setting.
In general, this assay should not be used to assess therapeutic success or failure, since nucleic acids from these organisms may persist for 3 weeks or more following antimicrobial therapy.
The presence of mucous does not interfere with this assay. However, this test requires endocervical cells, and if excess mucous is not removed prior to collection, adequate numbers of these cells may not be obtained.
No interference is expected due to:
-Lubricants and spermicides
The effects of use of tampons, douching, specimen types other than those listed in Specimen Required, and specimen collection variable have not been determined.
Testing of urine specimens with this method is not intended to replace cervical exam and endocervical sampling for diagnosis of urogenital infection; infections may result from other causes or concurrent infections may occur.
Testing urine specimens as the sole test for identifying female patients with chlamydial or gonococcal infections may miss some infected individuals.
Performance estimates for urine specimens are based on evaluation of urine obtained from the first part of the urine stream; performance on midstream collections has not been determined.
This assay does detect plasmid-free variants of Chlamydia trachomatis.
This assay does not detect Chlamydia pneumoniae.
This assay has not been shown to cross-react with commensal (nonpathogenic) Neisseria species in the oropharynx.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Centers for Disease Control and Prevention. 2002. Reporting of laboratory-confirmed chlamydial infection and gonorrhea by providers affiliated with three large Managed Care Organizations-United States, 1995-1999. MMWR Morb Mortal Wkly Rep 2002;51:256-259
2. Centers for Disease Control and Prevention: Sexually Transmitted Diseases Treatment Guidelines, 2010. MMWR Morb Mortal Wkly Rep 2010;59:RR12
3. Crotchfelt KA, Pare B, Gaydos C, Quinn TC: Detection of Chlamydia trachomatis by the GEN-PROBE AMPLIFIED Chlamydia trachomatis Assay (AMP CT) in urine specimens from men and women and endocervical specimens from women. J Clin Microbiol 1998 Feb;36(2):391-394
4. Gaydos CA, Quinn TC, Willis D, et al: Performance of the APTIMA Combo 2 assay for detection of Chlamydia trachomatis and Neisseria gonorrhoeae in female urine and endocervical swab specimens. J Clin Microbiol 2003 Jan;41(1):304-309
5. Chernesky MA, Jang DE: APTIMA transcription-mediated amplification assays for Chlamydia trachomatis and Neisseria gonorrhoeae. Expert Rev Mol Diagn 2006 Jul;6(4):519-525