**2. Diagnosis of chlamydial infections**

Several diagnostic techniques are available to diagnose chlamydia, including DNA amplification testing (NAAT), culture, antigen detection, and genetic probes; microscopy is not useful for this purpose. Nevertheless, NAAT is the preferred diagnostic technique due to its superior sensitivity, specificity, and wide availability [34, 35].

#### **2.1 Nucleic acid amplification testing (test of choice)**

DNA or RNA sequences from *C. trachomatis* are amplified using polymerase chain reaction (PCR), transcription-mediated amplification (TMA), or strand displacement amplification (SDA). The "gold standard" of diagnostics is to use these sensitive, specific tests if they are available [34, 36].

#### **2.2 The preferred testing specimen for diagnosis varies by syndrome**

#### *2.2.1 Genitourinary infection or screening in females*

A vaginal swab is the most appropriate specimen that the patient can collect. NAAT can be performed on either endocervical specimens (for example, cervical specimens collected into liquid cytology medium for Pap testing) or vaginal swabs for females undergoing speculum exams (for example, to evaluate symptoms of cervicitis). Compared to vaginal and endocervical swab samples, first-catch urine samples detect up to 10% fewer infections in females [36, 37].

#### *2.2.2 Test performance*

The NAATs can collect specimens without a pelvic examination in females [38]. The most sensitive specimen for diagnosing chlamydial infection in females is a swab of vaginal fluid [38, 39]. Compared with urine and, in some cases, endocervical swabs, NAAT on vaginal swab fluid on females had higher sensitivity than urine and, in some cases, endocervical swabs. Several studies have shown that NAAT on rectal specimens can detect rectal chlamydia more accurately than culture and still have high specificity [40]. Men who have sex with men (MSM) can also self-collect these samples to facilitate screening [41].

#### **2.3 Other diagnostic techniques**

#### *2.3.1 Rapid tests for chlamydia*

Even though NAAT has replaced culture as the new "gold standard," same-day results have not been available traditionally. NAAT-based rapid tests have been developed. Their use will likely be influenced by practical issues, such as waivers for non-laboratory use and cost, as they become more available [41].

#### *2.3.2 The XPert C trachomatis/N gonorrhea (CT/NG) assay*

A NAAT, the XPert C trachomatis/N gonorrhea (CT/NG) test provides results for chlamydia (and gonorrhea) within 90 minutes [42]. It is FDA-approved for use on vaginal and endocervical swabs. Using electrochemical detection technology, the Binx

#### Chlamydia trachomatis*: A Tiny Being beyond the Nature DOI: http://dx.doi.org/10.5772/intechopen.111425*

io CT/NG NAAT assay produces results within 30 min [43]. It is FDA-approved for use on vaginal swabs. 96, 99, 91, and 100% were the sensitivity, specificity, positive, and negative predictive values for CT. **Culture methods** for detecting chlamydiosis are now limited to research and reference laboratories due [44]. **Serology for C trachomatis** (complement fixation titers >1:64) is usually performed infrequently, is nonstandardized, and requires a high level of expertise for interpretation. Furthermore, it may not perform as well as a test to diagnose rectal infections in males as in females with upper genital tract infections [45–47]. **Testing for antigens requires** invasive methods such as cervix swabs or urethral swabs. Compared to culture, this method has an 80–95% sensitivity. Currently available **genetic probe methods** require invasive testing with a direct cervix or urethral swab since they do not amplify genetic targets. This assay is 80% more sensitive than culture. Although these tests are relatively inexpensive, their sensitivity is significantly lower than NAAT, and NAAT has become more cost-competitive, so they are no longer as commonly used.

Adolescent girls and young women may no longer be required to visit their doctors annually since there is no longer a need for annual cervical cancer screening. A young woman's annual visit is an important opportunity to obtain advice and information regarding her reproductive health, access contraception, receive counseling regarding sexually transmitted diseases (STDs), and to be screened for these diseases.
