C. trachomatis is divided into a number of serotypes, which correlate with the clinical syndrome they cause (Figure 1). For example, C. trachomatis, the major causal agent of the syndrome NGU, is currently the most common reportable infectious disease in the United States. C. trachomatis can also cause eye infections, with symptoms ranging from irritation to blindness. Trachoma, which is an ancient disease, was well described in Egyptian writings around 3800 B.C. It remains widely prevalent in developing areas of the world.

Fig1. Correlation between chlamydial species/serotypes and disease.

A. Clinical significance

 C. trachomatis causes a range of GU and eye infections.

 1. Nongonococcal urethritis: Annually, more than 4 million urogenital C. trachomatis infections occur in the United States in young, sexually active individuals of all socioeconomic groups. In men, the urethra is the initial site of infection. Women may present with cervicitis and/or urethritis. Infections are often asymptomatic, although communicable. [Note: Among women, the asymptomatic rate is higher than 50 percent.] Whether locally symptomatic or not, the infection may ascend into the upper reproductive tract to involve the epididymis in men and fallopian tubes and adjacent tissues in women (pelvic inflammatory disease). Chlamydial NGU is symptomatically similar to infections caused by Neisseria gonorrhoeae, although the average incubation time is longer (2 to 3 weeks), and the discharge tends to be more mucoid and contains fewer pus cells. In addition, the two infections often occur simultaneously. Therefore, patients suspected of chlamydial infection should be treated for gonococcal infection. NGU is caused by serotypes D–K of C. trachomatis (see Figure 1). These serotypes also cause eye infections, for example, in infants born to genitally infected women (Figure 2). Infection with C. trachomatis confers little protection against reinfection, which commonly occurs. Repeated or chronic episodes may lead to infertility in both sexes and to ectopic pregnancies.

Fig2. Neonatal conjunctivitis due to chlamydial infection.

2. Lymphogranuloma venereum: C. trachomatis serotypes L1, L2, and L3 cause lymphogranuloma venereum (LGV), a more invasive sexually transmitted disease. It is uncommon in the United States but endemic in Asia, Africa, and South America. LGV is characterized by transient papules on the external genitalia, followed in 1 to 2 months by painful swelling of inguinal and perirectal lymph nodes. Adenopathy (swelling of the lymph nodes) is often accompanied by mild constitutional symptoms. The inguinal ligament often forms a cleft known as the “groove sign” between masses of inguinal lymph nodes. The affected lymph nodes suppurate (to form or discharge pus), and chronic inflammation and fibrosis lead to extensive ulceration and blockage of regional lymphatic drainage.

3. Trachoma: C. trachomatis, serotypes A, B, Ba, and C cause a chronic keratoconjunctivitis that often results in blindness. Trachoma is transmitted by personal contact, for example, from eye to eye via droplets, by contaminated surfaces touched by hands and conveyed to the eye, or by flies. Because of persistent or repeated infection over several years, the inflammatory response with attendant scarring leads to permanent opacities of the cornea and distortion of eyelids.

 4. Neonatal conjunctivitis and other infections: Over 50 percent of infants born to women infected with C. trachomatis, serotypes D–K (see Figure 1) will contract symptomatic infection on pas sage through the birth canal. The most common presentation is inclusion conjunctivitis of the newborn (see Figure 2). This acute, purulent conjunctivitis (named for the inclusion bodies seen in infected conjunctival epithelial cells) usually heals after appropriate antimicrobial therapy, without permanent dam age to the eye. If untreated, the infection can lead to permanent scarring of the cornea or conjunctiva. Approximately 1 of 10 infected infants will present with or develop pneumonia, which can be treated with erythromycin.

 5. Inclusion conjunctivitis in adults: Individuals of any age may develop transient purulent conjunctivitis caused by C. trachomatis serotypes D–K (see Figure 1). Such individuals are often found to be genitally infected as well.

B. Laboratory identification

  C. trachomatis can be demonstrated in clinical material by several direct procedures and by culturing in human cell lines. Samples, particularly from the urethra and cervix in GU infection and conjunctivae in ocular disease, should be obtained by cleaning away overlying exudate and gently scraping to collect infected epithelial cells.

1. Direct tests: Microscopic examination using direct fluorescent anti body staining reveals characteristic cellular cytoplasmic inclusions. C. trachomatis infections can be detected with high sensitivity and specificity using DNA amplification performed on urine specimens. This permits cost-effective screening of large numbers of individuals without the need for access to a medical clinic and a pelvic examination. Figure 3 shows the high prevalence of infection among young females.

Fig3. Prevalence of chlamydial infection in the United States (2010). A. by sex; B. Among females according to age.

 2. Culturing methods: C. trachomatis can be cultivated by tissue culture in several human cell lines. In the standard procedure using McCoy cells, addition to the culture medium of a eukaryotic metabolic inhibitor, such as cycloheximide, enhances growth of the parasite. The presence of chlamydial inclusions can be demonstrated after 2 to 7 days of incubation.

 3. Detection of serotypes: Serotypes of C. trachomatis can be determined by immunofluorescence staining with monoclonal antibodies. However, the procedure is not widely used because it adds little to clinical impressions. Serologic testing for specific antibodies is similarly not helpful except in suspected LGV, in which a single high-titer response is diagnostic.

 C. Treatment and prevention

 Chlamydiae are sensitive to a number of broad-spectrum antibacterials. Azithromycin and tetracycline are currently the drugs of choice. Resistant strains have not been reported in the clinical setting. Erythromycin should be used in small children and pregnant women because of the effects of tetracyclines on teeth and bones. The only recommended treatment for a concurrent gonococcal infection is with ceftriaxone. A topical ocular preparation containing erythromycin provides moderately effective prophylaxis in newborns. Detection (a particular problem in asymptomatic individuals) followed by specific treatment is the key means of control.

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