C. trachomatis serovars D–K cause sexually transmitted diseases, especially in developed countries, and may also produce infection of the eye (inclusion conjunctivitis). In sexually active men, C. trachomatis causes nongonococcal urethritis and, occasionally, epididymitis. In women, C. trachomatis causes urethritis, cervicitis, and pelvic inflammatory disease, which can lead to sterility and predispose to ectopic pregnancy. Proctitis and proctocolitis may occur in men and women, although these infections appear to be most common in men who have sex with men. Any of these anatomic sites of infection may give rise to symptoms and signs, or the infection may remain asymptomatic but communicable to sex partners. Up to 50% of nongonococcal urethritis (men) or the urethral syndrome (women) is attributed to chlamydiae and produces dysuria, nonpurulent discharge, and frequency of urination. Genital secretions of infected adults can be self inoculated into the conjunctiva, resulting in inclusion conjunctivitis, an ocular infection that closely resembles acute trachoma.

The newborn acquires the infection during passage through an infected birth canal. Probably 30–50% of infants of infected mothers acquire the infection, with 15–20% of infected infants manifesting eye symptoms and 10–40% manifesting respiratory tract involvement. Inclusion conjunctivitis of the newborn begins as a mucopurulent conjunctivitis 5–12 days after delivery. It tends to subside with erythromycin or tetracycline treatment or spontaneously after weeks or months. Occasionally, inclusion conjunctivitis persists as a chronic chlamydial infection with a clinical picture indistinguishable from that of subacute or chronic childhood trachoma in non endemic areas and usually not associated with bacterial conjunctivitis.

Laboratory Diagnosis

A. Specimen Collection

 Proper specimen collection is the key to the laboratory diagnosis of chlamydia infection. Because the chlamydiae are obligate intracellular bacteria, it is important that the specimens contain infected human cells as well as the extracellular material where they might also be present. Endocervical specimens should be collected after removal of discharge and secretions from the cervix. A swab or cytology brush is used to scrape epithelial cells from 1 to 2 cm deep into the endocervix. Dacron, cotton, or rayon on a plastic shaft should be used to collect the specimen; some other swab materials (calcium alginate) and wooden shafts are toxic to chlamydiae. A similar method is used to collect specimens from the vagina, urethra, or conjunctiva. The commercial diagnostic nonculture tests for chlamydia do not require viable organisms. In general, these proprietary tests include the specimen collection swabs and transport tubes that have been demonstrated to be suitable for the specific tests. For culture, the swab specimens should be placed in a chlamydiae transport medium, such as 2-sucrose phosphate supplemented with bovine serum and antibiotics that inhibit normal microbiota, and kept at refrigerator temperature before transport to the laboratory.

Urine can be tested for the presence of chlamydial nucleic acid. Only the first 20 mL of the void should be collected because a larger volume of bladder urine would dilute the initial urine that passes through the urethra; this could result in a negative test result because of the dilution.

B. Nucleic Acid Detection

 Nucleic acid amplification tests (NAATs) are the tests of choice for the diagnosis of genital C. trachomatis infections. There are at least five U.S. Food and Drug Administration (FDA)-cleared assays in the United States. They use a variety of molecular methods that target the C. trachomatis cryptic plasmid or 23SrRNA, including PCR, strand displacement, and transcription-mediated amplification. These tests have become widely used and have replaced most of the nonamplification methods. Although they are highly sensitive and specific, they are not perfect.

Specimen types that are appropriate for testing by NAATs include first void urine from males and females and vaginal, cervical, and urethral swabs. Some of the commercial companies that market these platforms are in the process of validating or have validated extragenital sources such as conjunctival, oropharyngeal, and rectal samples. The nucleic acid detection tests have been adapted to simultaneously detect Neisseria gonorrhoeae.

C. Direct Cytologic Examination (Direct Fluorescent Antibody) and Enzyme-Linked Immunoassay

Commercially available direct fluorescent antibody (DFA) and enzyme-linked immunoassay (EIA) assays to detect C. trachomatis continue to be marketed. The DFA uses mono clonal antibodies directed against a species-specific antigen on the chlamydial MOMP. The EIA detects the presence of genus-specific antigens extracted from EBs in the specimen. DFA remains useful for detection of chlamydiae in extragenital samples, such as conjunctival swabs. Because of their very low sensitivity and the widespread availability of the more sensitive NAATs, EIAs are being phased out as acceptable methods for screening for both chlamydia and gonorrhea.

D. Culture

 Culture of C. trachomatis has historically been used to diagnose chlamydia infections. Culture, however, is costly and arduous. Results are delayed compared with the timeliness of NAATs and other tests. Culture is generally much less sensitive than NAATs; the degree of lower sensitivity is largely dependent on the culture method used. Culture is now done in a limited number of reference laboratories. A number of susceptible cell lines can be used, most often McCoy, HeLa 229, or HEp-2. The cells are grown in monolayers on coverslips in dram or shell vials. Some laboratories use flat-bottomed microdilution trays, but cultures by this method are not as sensitive as those achieved with the shell vial method. The cells are treated with cycloheximide to inhibit metabolism and increase the sensitivity of isolation of the chlamydiae. The inoculum from the swab specimen is centrifuged onto the monolayer and incubated at 35–37°C for 48–72 hours. A second monolayer can be inoculated, and after incubation, it can be sonicated and passaged to another monolayer to enhance sensitivity. The monolayers are examined by direct immunofluorescence to visualize the cytoplasmic inclusions. Chlamydial cultures by this method are about 80% sensitive but 100% specific.

E. Serology

Because of the relatively great antigenic mass of chlamydiae in genital tract infections, serum antibodies occur much more commonly than in trachoma and are of higher titer. A titer rise occurs during and after acute chlamydial infection. Because of the high prevalence of chlamydial genital tract infections in some societies, there is a high background of antichlamydial antibodies in the population; serologic tests to diagnose genital tract chlamydial infections generally are not useful.

In genital secretions (eg, cervical), antibody can be detected during active infection and is directed against the infecting immunotype (serovar).

Treatment

 It is essential that chlamydial infections be treated simultaneously in both sex partners and in offspring to prevent reinfection. Tetracyclines (eg, doxycycline) are commonly used in nongonococcal urethritis and in nonpregnant infected women. Azithromycin is effective and can be given to pregnant women. Topical tetracycline or erythromycin is used for neo natal N. gonorrhoeae infections but may not effectively prevent neonatal C. trachomatis infection. Systemic therapy should be used for inclusion conjunctivitis because topical therapy may not cure the eye infections or prevent respiratory disease.

Epidemiology and Control

 Genital chlamydial infection and inclusion conjunctivitis are sexually transmitted diseases that are spread by contact with infected sex partners. Neonatal inclusion conjunctivitis originates in the mother’s infected genital tract. Prevention of neonatal eye disease depends on diagnosis and treatment of the pregnant woman and her sex partner. As in all sexually transmitted diseases, the presence of multiple etiologic agents (eg, gonococci, treponemes, trichomonads, and herpes sim plex viruses) must be considered. Instillation of erythromycin or tetracycline into the newborn’s eyes does not prevent development of chlamydial conjunctivitis. The ultimate control of this—and all—sexually transmitted disease depends on safe sex practices and on early diagnosis and treatment of infected persons. To accomplish the latter, the Centers for Disease Control and Prevention recommends annual screening of all sexually active women ages 25 years and younger.

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مواضيع ذات صلة

Chlamydia psittaci and Psittacosis

Chlamydia Pneumonia and Respiratory Infections

Trachoma

Coxiella burnetii

Ehrlichia and Anaplasma

Rickettsia and Orientia

Cultivation of Mycoplasma and Ureaplasma

Laboratory Diagnosis of Mycoplasma and Ureaplasma

Epidemiology and Pathogenesis of Mycoplasma and Ureaplasma

Tropheryma whipplei

Mycoplasma Pneumonia and Atypical Pneumonias

Leptospira and Leptospirosis