New diagnostic tests for gonorrhea and chlamydia

Abstract

Genitourinary infections caused by Neisseria gonorrhoeae and Chlamydia trachomatis pose significant public health problems in this country. Our ability to effectively screen for, and prevent the spread of, these organisms depends on the availability of accurate and efficient detection methods. Culture has been the traditional reference standard for both organisms and has the advantage of 100% specificity. Gonorrhea culture is very inexpensive, whereas chlamydia culture is moderately expensive. The disadvantages of culture include variable sensitivity, complex logistics, and slow turnaround times. Antigen detection methods, such as direct fluorescent antibody testing and enzyme immunoassay, have fast turnaround times and simplified logistics but lower sensitivity than culture. Recently developed tests using nucleic acid technology offer the potential for improved sensitivity, ease of handling, and rapid processing at costs comparable to, or less than, antigen detection methods. Hybridization techniques utilize fluorescent DNA probes that bind directly to species-specific ribosomal RNA. The polymerase chain reaction (PCR) and ligase chain reaction (LCR) amplify species-specific DNA sequences prior to detection. The hybridization techniques are the least expensive and appear to have similar accuracy to PCR and LCR. Polymerase chain reaction and LCR may be performed on first-catch urine samples, which offer the advantages of ease of collection and greater yield of organisms. Urine samples typically contain organisms inhabiting both the urethra and endocervix, whereas endocervical specimens do not contain organisms in women who are colonized solely in the urethra. Endogenous inhibitors limit the sensitivity of the amplification techniques. If their effect could be eliminated, PCR and LCR would provide clear clinical advantages over any of the other methods in use.