Chlamydia is the most common sexually transmitted disease. Yet, many people with this infection are not aware of it because they have no symptoms. As a result, chlamydia often goes untreated, which can lead to serious complications. On the other hand, virtually all cases can be treated successfully and inexpensively with antibiotics. Thus, widespread testing for chlamydia, even among those without symptoms, is clearly beneficial.
The CDC recommends routine chlamydia testing for:
- all women with cervical discharge containing both mucus and pus;
- all sexually active women under the age of 20;
- those with a prior history of a sexually transmitted disease;
- those with multiple sexual partners;
- those with a new sex partner in the past three months; and
- those who do not consistently use barrier contraceptives (those that physically block sperm from fertilizing an egg, such as a condom).
How Is Chlamydial Infection Detected?
Successfully screening for and preventing the spread of chlamydia depends on the ability to diagnose infections accurately, rapidly, and inexpensively. Several tests are available for diagnosing chlamydia, each with their own advantages and drawbacks. The best diagnostic method for you may depend on the clinical setting, desire for accuracy, the test's cost, and the prevalence of the infection within the population.
Until recently, a cell culture was considered the most accurate way to diagnose Chlamydia trachomatis infections and the standard against which all other tests were measured. In this method, cells taken from the affected part of the body are grown (cultured) on a glass surface in the laboratory to identify abnormalities. The main advantage of a cell culture is that it always excludes chlamydial infection when it is truly absent. For this reason, cell cultures remain the diagnostic method of choice in cases with legal implications, such as rape or incest. However, cell cultures for chlamydia are moderately expensive and have at least a three-day waiting period for results. Furthermore, this method only detects infection 70 to 80% of the time because the requirements for collection, storage, and transport are stringent and not always met.
Two diagnostic methods use immunologic technology as a way to detect molecules on the surface of C. trachomatis.
- The enzyme immunoassay involves detecting enzymes that are part of the bacterium, and thus, markers for its presence in a patient's blood. Like other kinds of serology (testing for antibodies or pathogens in the serum), this automated method is objective, quick, and easy to perform. However, the accuracy rate is lower than that of a culture.
- The Direct Fluorescent Antibody (DFA) assay identifies components of antibodies to a specific pathogen in the serum. The presence of antibodies (produced by the immune system) to C. trachomatis indicates infection. Although an individual sample can be processed fairly rapidly, this method is not suitable for screening large numbers of specimens because it is labor-intensive and requires a certain amount of skill to be interpreted accurately. Also, like the enzyme immunoassay, Direct Fluorescent Antibody is not as accurate as a cell culture.
- DNA Probes and Tests
Newer tests that employ DNA technology offer the potential for improved sensitivity, ease of handling, and rapid processing at costs comparable to-or lower than-the immunologic methods.
In DNA probe methods, cloned or synthetic genes are used as ?probes? that bind to parts of the nucleic acid of an organism. A lab scientist is then able to identify the organism. DNA probes are the least expensive of all the chlamydia diagnostic tests. They are rapidly performed, well suited for large populations, and are as accurate as a cell culture. Furthermore, gonorrhea can be analyzed from the same sample. The main disadvantage of the DNA probe is the high cost of the equipment needed to process samples and detect infectious agents.
Nucleic acid amplification techniques offer the greatest promise for the future. Of these, the polymerase chain reaction (PCR) has been studied the most. Often used in forensic medicine, the PCR method involves taking a cell sample, isolating its genetic material, and then replicating it. This makes the cell's genetic code (and the infectious agent itself) easier to identify. This method has some advantages:
- detection is improved because chlamydia DNA replicates between the time a serum sample is collected and tested, resulting in more infected genetic material; and
- PCR can be performed on urine or vaginal swab samples, which are easier to collect than cervical swabs.
However, one disadvantage is that urine and vaginal samples typically contain organisms from both the urethra and endocervix (the membrane that lines the cervix), which makes isolating the infection's location more difficult.
The ability of PCR to detect chlamydia is at least equal to-and probably greater than-a cell culture. Although PCR is relatively labor-intensive, with a four- to five-hour processing time, it costs the same as the enzyme immunoassay. Fully automated systems are currently being developed, which will reduce cost and turnaround time. If researchers can find a way to overcome the effect of inhibitors, PCR will provide clear clinical advantages over any of the other methods currently used.