Inoculation of cell cultures with a genital specimen has been the conventional method for the laboratory diagnosis of C. trachomatis. This method was popularized during 1970s and 1980s. Relative to newer methods, the conventional approach entails more expense and is more labor intensive and time consuming (2 to 3 days). It also requires considerable manual expertise to perform the meticulous handling of the specimen during transport to maintain viability of inoculated organisms as well as cell cultures. Enzyme immunoassays (EIAs) and direct fluorescence assays (DFAs) are antigen detection methods that are still commonly used in many clinical diagnostic laboratories (Newhall et al., 1999; Van Dyck et al., 2001). Both methods bear less stringent demands on transport requirements, and test results can often be obtained on the same day. As specimens are transported stably under ambient conditions, EIA is suitable for public health laboratories covering large geographic areas. It is also inexpensive because specimens can be processed in batch using automated equipment (Newhall et al., 1999). Because the test is based on the detection of chlamydial genus-specific lipopolysaccharide (LPS) using monoclonal or polyclonal antibodies linked to a solid-phase support, chlamydial LPS antibodies may also cross-react with the LPS of other Gramnegative bacteria to give false-positive results. Either DFA or blocking assays are needed to confirm positive EIA results and thus improve specificity. On the other hand, EIA lacks sensitivity as screening assay, especially for asymptomatic men, possibly due to its lower detection limit of 10,000 elementary bodies (Lin etal., 1992).
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