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NEWS AND FILLER
Year : 2009  |  Volume : 30  |  Issue : 1  |  Page : 61-64
 

Diagnostic approach to gonorrhoea: Limitations


1 Department of Microbiology, AIIMS, India
2 Regional STD Teaching, Training and Research Center, VMMC & SJH, India
3 Department of Dermatology and Venerology, AIIMS, India

Date of Web Publication5-Sep-2009

Correspondence Address:
Seema Sood
Department of Microbiology, AIIMS, Ansari Nagar, New Delhi
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0253-7184.55475

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How to cite this article:
Verma R, Sood S, Manjubala, Kapil A, Sharma V K. Diagnostic approach to gonorrhoea: Limitations. Indian J Sex Transm Dis 2009;30:61-4

How to cite this URL:
Verma R, Sood S, Manjubala, Kapil A, Sharma V K. Diagnostic approach to gonorrhoea: Limitations. Indian J Sex Transm Dis [serial online] 2009 [cited 2019 Nov 19];30:61-4. Available from: http://www.ijstd.org/text.asp?2009/30/1/61/55475


Gonorrhoea is one of the oldest known bacterial sexually transmitted infections (STIs) that continue to cause a significant morbidity among the sexually active individuals. [1] A total of 62 million cases of gonococcal infections are estimated to occur each year globally, attesting to the public health importance of  Neisseria More Details gonorrhoeae ( N. gonorrhoeae ) . Rates of gonorrhoea vary greatly among developed and developing countries. The highest rates are in South and South-East Asia, sub-Saharan Africa, and Latin America. [2] However, the actual burden of STIs remains unknown in India. Prevalence data is available only for certain population groups from ad hoc surveys, which may not be a true representation of the total population. Based on these, the prevalence rate in women in facility-based samples varies from 0-16.5%, and in community it varies from 0-4.2%. [3],[4],[5] For men in the community, the prevalence rate varies from 1.7-2.1%, and in STD clinics it ranges from 8.5-25.9%.[5],[6] However, gonorrhoea is substantially under-diagnosed and under-reported, and approximately twice as many infections are estimated to occur each year. [7]

Currently, India is in the throes of a human immunodeficiency virus (HIV) epidemic. Numerous epidemiological studies suggest that there is approximately two- to five-fold greater risk of acquiring HIV in the presence of gonorrhoea. Early and appropriate diagnosis and treatment of gonorrhoea is an integral part of any quality and comprehensive HIV prevention strategy.[8],[9],[10],[11],[12] Although, a syndromic approach has been recommended that uses clinical algorithms based on a STD syndrome, the constellation of patient symptoms and clinical signs, to determine antimicrobial therapy. It is proven now that it does not perform well with women. Further attempts to infer a presumptive aetiological diagnosis based on clinical manifestations eliminate the laboratory component and thus, eliminates the treatment delays associated with aetiological management; but they are often inaccurate or incomplete. [13],[14]

The principal strategy for the control of gonorrhoea involves the diagnosis and treatment of symptomatic cases together with contact tracing and treatment of sexual partners. But these methods are failing to prevent the transmission of infection, as a majority of women (50-80%) together with a proportion of men (~10%) infected with N. gonorrhoeae , are asymptomatic. [2],[15] The lack of a sensitive and specific test suitable for mass screening and/or a vaccine to protect individuals at high risk, are two of the most important factors contributing to our failure to control this disease. [16]

Although, the urethra and the uterine cervix serve as the initial sites for gonococcal infection in men and women, respectively, infections of the conjunctiva, pharynx, and rectal mucosa are also reported. N. gonorrhoeae infection of these distinctly different epithelial cell surfaces leads to a spectrum of clinical manifestations of the disease. Gonorrhoea presents as lower genital tract infection, pelvic inflammatory disease (PID), and related sequelae in women, urethritis, and epididymitis in men; and proctitis, pharyngitis, conjunctivitis, and disseminated gonococcal infection, in both sexes. Disseminated disease, although uncommon, can cause arthritis-dermatitis syndrome, endocarditis, and/or meningitis. Newborn infants may develop gonococcal ophthalmia. [17],[18] It usually produces purulent exudates, but signs and symptoms of the disease may either be absent or indistinguishable from those of chlamydial infection. Therefore, laboratory procedures are needed for diagnosis. Until recently, little effort was placed on developing the improved methods of diagnosis.

Currently, tools for gonorrhoea diagnosis include microscopy, culture, and various other nonculture methods, which are usually performed on invasive specimen (endocervical and urethral swabs). However, serology is not useful for the diagnosis of this infection. [19]

Microscopy is a rapid point of care test that can be performed at bedside and facilitates the treatment of N. gonorrhoeae infection in patients at the first clinical visit. The microscopic diagnosis of gonococci is based on the cell morphology and arrangement, location, and color of the bacterial cells. Gonococci are mainly identified as gram-negative coffee bean-shaped diplococci, with concave sides opposing each other. Location of gonococci (mainly inside the polymorphonuclear leucocytes) is of crucial significance in the microscopic diagnosis of gonorrhoea. If only extracellular diplococci are identified, culture must be performed for definitive diagnosis.

It is important to remember that though microscopy works well with symptomatic men giving sensitivity, as high as, approximately 95%, and a specificity of 99%, the sensitivity is greatly reduced in asymptomatic patients (40−60%). Also, for the endocervical or urethral samples from women microscopy is not a recommended technique of diagnosis due to the low sensitivity and insufficient specificity (~40%).

Culture is still considered to be the "Gold Standard" for the definitive diagnosis of gonorrhoea. The sensitivity of culture is 85−95% for acute infection and the specificity is 100% under optimal conditions. [14],[20] Although, the methods of gonococcal culture have been well described, there are certain disadvantages of culture-based identification methods. These include the fastidiousness of the organism, which makes successful growth less likely if isolation media, specimen transport, and laboratory techniques, are not optimal. In addition, multiple steps are necessary for processing specimens, and the quality assurance needs to be addressed at each step. Also, the time duration necessary from specimen collection to reporting of results is long, i.e., at least 48-72 hours, thereby resulting in delays in diagnosis and treatment. The sensitivity of culture falls to approximately 50% in women with chronic infections. Additional sources of infection often go undetected because appropriate culture sites are not included, such as the pharynx and rectum. [2],[15],[21] Further, the regional laboratories are usually not equipped to culture N. gonorrhoeae. Despite the introduction of molecular tests in 1990s, identification of N. gonorrhoeae by culture, is important for the retention of the organism for other tests, such as for determination of antimicrobial susceptibility and subtyping.

Nonculture tests: Several nonculture tests have been introduced as possible alternatives to gonococcal culture. The enzyme immunoassay (introduced by Abbott Diagnostics as Gonozyme) was withdrawn because of poor sensitivity. Next came the generation of nucleic acid hybridization assays, the GeneProbe PACE II and the Diagene Hybrid Capture II assays. The reported sensitivity and specificity values for these tests suggest that they are not as sensitive or specific as culture.[20],[22] Further, sophisticated DNA technologies, especially nucleic acid amplification (PCR and Ligase chain reaction), have been developed and evaluated in many countries over the past few years. The commercially available Ligase chain reaction (LCR) test (by Abbott Laboratories) has been withdrawn because of issues related to quality assurance. [22] Polymerase Chain Reaction (PCR) for gonorrhoea is not only available commercially but many laboratories have designed in-house tests for the detection of this pathogen. Most popular test available is the Roche Cobas Amplicor assay. This test lacks the desired specificity as it cross- reacts with commensal species such as N. cinerea and N. subflava and also with Lactobacilli .[23],[24] Other commercially available tests for diagnosis include the Becton Dickinson ProbeTec SDA assay and the fully automated Gen-Probe APTIMA Combo 2 (AC2) assay. Regarding in-house assays, some groups are also working on formulation of diagnostic PCR targeting the CppB plasmid. However, approximately 10% of N. gonorrhoeae strains do not carry the CppB plasmid. It has also been observed that homology exists between the sequences of N. gonorrhoeae cryptic plasmid and the plasmids present in the other species of Neisseria .[21],[23],[25] Other strong candidates for diagnosis using PCR are the Opa gene and the porA pseudogene. Comparison of assays based on detection of Opa gene with 16S rRNA PCR has shown a five-fold higher sensitivity of the Opa assay, maybe due to a higher copy number. [21],[25] The use of porA pseudogene as a PCR candidate is still in the evaluation phase.

To date, PCR has been the most widely used amplification method and is being carried out in various laboratories worldwide for the diagnosis of gonorrhoea. The diagnostic performance of PCR for gonococcal infection detection has been evaluated with invasive endocervical and urethral swab specimens, and more recently with urine specimens. Several studies have shown that PCR assays perform well in detecting gonococcal infection on the invasive genital specimens, but the sensitivity decreases considerably, giving upto 50% false negatives, when urine samples were used. [25] This may be due to the inhibitors present in urine such as b-human chorionic gonadotropin, crystals, polysaccharides, humic acid, urea, hemoglobin, and nitrites. The false negativity was especially high in case of urine samples collected from women. The speculation made to explain the poor results obtained was that urethra is not the main site for N. gonorrhoeae infection in females. [24] The other problems associated with PCR assays are that they are expensive, require specialized equipment, and trained manpower. PCR has been tested only on symptomatic patients, therefore its performance in asymptomatic patients is not known. Besides, a high false positivity of PCR has been reported especially in commercial assays. Therefore, it is recommended as per the Public Health Laboratory Network (PHLN) guidelines laid down by National Neisseria Network, Australia that all commercial screening assays that are positive should also be positive on a reliable supplemental assay before a positive result is reported. [25]

Further, for the purpose of test evaluation, true positives should be defined by one or more of the following criteria:

  • Culture positive using contemporary isolation and identification techniques
  • Positive result on nucleic acid detection tests (NADTs) directed to targets on three different genes that are known to have discriminatory capacity
  • Sequencing of a gene known to separate gonococcal from nongonococcal species
The last two recommendations are feasible only in research setups that are equipped with specialized equipment and trained manpower. According to the WHO Western Pacific Region manual of tests for the detection of reproductive tract infection, an ideal diagnostic test is one that is rapid enough for the results to be available while the patient waits, as well as, being easy to perform, inexpensive, highly sensitive and specific, and requiring no specialized equipment. It should use samples obtained by noninvasive procedures. The results should be reliable, reproducible, and robust. Additionally, in the case of gonorrhoea, it should include determination of antibiotic susceptibility. [26],[27] Clearly, a single test with all of these characteristics does not yet exist.

 
   References Top

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2.WHO. Global prevalence and incidence of selected curable sexually transmitted infections: Overview and Estimates. Geneva: World Health Organization, 2001.  Back to cited text no. 2    
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24.Mukenge-Tshibaka L, Alary M, Bernier F, van Dyck E, Lowndes CM, Guédou A, et al . Diagnostic performance of the Roche AMPLICOR PCR in detecting Neisseria gonorrhoeae in genitourinary specimens from female sex workers in Cotonou, Benin. J Clin Microbiol 2000;38:4076-9.  Back to cited text no. 24    
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26.Mabey D, Peeling RW, Ustianowski A, Perkins MD. Diagnostics for the developing world. Nat Rev Microbiol 2004;2:231-40.  Back to cited text no. 26    
27.WHO/WPRO. STI/HIV: Laboratory tests for the detection of reproductive tract infections 1999.  Back to cited text no. 27    




 

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