Sunday, November 17, 2019

Chlamydia Infection Diagnosis

Chlamydia Infection Diagnosis
Early diagnosis and treatment of sexually transmitted diseases is a key intervention for its prevention and control. The NCSP promotes tests for chlamydia, the most commonly diagnosed bacterial STI, in sexually active youth on an annual or partner basis

Chlamydia infections are related with a wide group of diseases. C. trachomatis (serovar A, B, Ba and C) causes trachoma, the leading global cause of infectious blindness. D to K serovars are most commonly associated with sexually transmitted diseases and can cause infertility in women if left untreated. C. Trachomatis infection diagnosis and detection in women are difficult because it is asymptomatic in 80% from them . Chlamydia has a high prevalence among young men and women and over 13.5% of women <25 years of age have lower genital tract infections. Screening for women with C. trachomatis lower genital tract infection is important for preventing PID, ectopic pregnancy and infertility

Diagnosis of chlamydia infections

Clinical syndromes, such as non-gonococcal urethritis or mucopurulent cervicitis, can be diagnosed on the basis of clinical signs and symptoms, if supported by microscopic results of leukocytosis. However, chlamydia infections are often asymptomatic, so diagnosis generally requires identification / confirmation of specific laboratory tests for chlamydia. Use caution, particularly in low risk patients and in patients with low prevalence populations, to confirm positive test results to reduce the risk of false positives

Many tests are available today to detect C. trachomatis infection in a wide variety of samples. Urogenital infections in women can be diagnosed by testing urine or swab specimens from the cervix or vagina. In men, urine tests or samples from the urethra can be used. Rectal infection can be diagnosed using rectal swabs. However, there are significant differences in their respective ability to detect infections. The selection of the appropriate test and the need for possible confirmatory tests largely depend on the prevalence of infection in local populations. Therefore, familiarity with the different tests and their properties is needed to improve detection of infected individuals and reduce false positive results

Chlamydia Tests include:

Cell culture test. This old test is reliable but takes 48 to 72 hours to complete. Chlamydia infections can also be diagnosed by culture. The specimen must be grown in tissue culture since C. trachomatis is a mandatory intracellular organism and therefore cannot grow in artificial soils. Culture allows you to test antibiotic sensitivity and genotyping, which can be important for public health reasons. After 48 to 72 hours of growth, infected cells develop characteristic intracytoplasmic inclusions that contain substantial amounts of elemental and crosslinked bodies of C. trachomatis. These unique inclusions are detected by staining with a monoclonal antibody conjugated to fluorescein specific for the main outer membrane protein (MOMP) of C. trachomatis. Cell culture methods vary from laboratory to laboratory, leading to a likely substantial interlaboratory variation in performance

NAATs demonstrate that the common feature among NAATs is that they are designed to amplify nucleic acid sequences that are specific to the detected organism. Like other non-cultural tests, NAATs do not require viable organisms. The increased sensitivity of NAATs is attributable to their ability to produce a positive signal from a single copy of the target DNA or RNA. NAATs test a single nucleic acid (DNA or RNA) from the chlamydic organism or use a probe attached to the target nucleic acid. NAATs are very sensitive; I am able to detect a single genetic copy. NAATs are also very specific. There are several types of NAAT. The two most used tests are the polymerase chain reaction (PCR) and the ligase chain reaction (CSF). PCR amplifies the nucleic acids found in C. trachomatis' elementary body (EB)

Therefore, if a cure test is needed, it should be delayed until all DNA / RNA of chlamydia disappears, which generally takes more than 3 weeks. Direct staining of fluorescent antibodies (DFA). This test is faster than the traditional cultivation test. Depending on the commercial product used, the antigen that the antibody detects in the C. trachomatis DFA procedure is the MOMP or LPS molecule. The sample material is obtained with a swab or an endocervical brush, which is then wound onto the sample on a slide. After the slide has dried and the fixative has been applied, the slide can be stored or shipped at room temperature

The laboratory should process the slide within <7 days of obtaining the sample. A further advantage of DFA is that the quality of endocervical smears can be assessed by checking for the presence of cells in the column. DFA is best suited for labs that analyze a limited number of samples, as the procedure is tiring and time consuming. DFA tests have not been established as an initial test for the direct detection of N. gonorrhoeae in clinical specimens

Enzyme immunoassay (EIA). It is easy to perform and even faster than the traditional cultivation test, but it is not so precise. A considerable number of EIA tests have been marketed to detect C. trachomatis infection. C. trachomatis EIA tests disclose LPS from chlamydia with a monoclonal or polyclonal antibody that has been classificated as an enzyme. The enzyme converts a colorless substrate into a colored product, which is detected by a spectrophotometer. Samples can be stored and transported without refrigeration and must be processed within the times indicated by the manufacturer

A disadvantage of EIA methods that detect LPS is the potential for false positive results caused by the cross-reaction with LPS of other microorganisms, including other Chlamydia species. The manufacturers have developed blocking tests that verify the positive results of the VIA tests. The test is repeated on positive samples with the addition of a monoclonal antibody specific for LPS chlamydia. EIA tests should not be used with rectal specimens due to cross-reactions with faecal bacteria

DNA probe. This test is expensive but is more specific and convenient than culture, VIA or DFA tests. Genital sweep samples are not required. Urine tests can provide accurate results. The most common commercial test for C. trachomatis is the DNA probe, which uses nucleic acid hybridization to detect DNA from chlamydia from urogenital swabs. The DNA probe detects an infection with samples that have a minimum of 1000 EB. It has a sensitivity of 85-90% and a specificity of 98-99% with respect to culture and a sensitivity of 77-93% with respect to NAAT. Since false positive rates with DNA probes are high, the CDC recommends that the positive results of DNA probe tests in low prevalence populations be confirmed with a second test.
Serological tests

Serology has a limited value in tests for uncomplicated genital C. trachomatis infection and should not be used for screening since a previous chlamydial infection often causes long-lasting antibodies that cannot be easily distinguished from the antibodies produced in a current infection. More specific information on serological tests for C. trachomatis antibody has been reported elsewhere. Serological or diagnostic tests for N. gonorrhoeae are not available

Anti-C antibodies. trachomatis can be analyzed in serum. Chlamydia antibody serology is not useful for detecting acute infection due to poor specificity and reproducibility. serology is unable to distinguish between active infection and resolved infection. Serology can be helpful in assessing whether possible tubular factors are causing a woman's infertility and helping determine who could benefit from hysterosalpingography


It is common for people to infect sexual partners, as chlamydia infection is often present in the absence of symptoms. Chlamydia prevention programs have been implemented to reduce the burden of reproductive sequelae resulting from chlamydia infection. Since most reproductive complications of chlamydia occur in women and most infections are asymptomatic, the cornerstone of chlamydia prevention is the detection of infection in young women. Nucleic acid amplification diagnostic tests are the preferred diagnostic tests because of their superior sensitivity and can be performed on easily collected samples, such as urine or vaginal swabs

Researchers are studying topical microbicides and a vaccine as ways of preventing infection. An urgent research priority is also the development of a simple and inexpensive test for the diagnosis of chlamydia infection

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