By Gerardo Salinas


Chlamydia is an infection caused by the bacterium Chlamydia trachomatis. Chlamydia is most commonly spread through sexual contact (anal, oral, vaginal). It also can be spread from mother to newborn via the vaginal tract during birth. Chlamydia infections affect the genital tracts of men and women, but also can affect the eyes of newborns whom are infected by their infected mothers during birth. According to the Center for Disease Control (CDC), Chlamydia infections are the most prevalent of all sexually transmitted diseases (STDs) reported in the United States since 1994 (1). In 2006 alone 1,030,911 Chlamydia cases were reported to the CDC from the 50 states and the District of Columbia (1). This was the first time that Chlamydia infections exceeded 1 million cases (1). In 2006, Texas ranked 25th in the United States with 75,543 cases, 6022 more cases than it had in 2002 (1). The Austin-Round Rock area had 7,325 reported cases in 2006, 2,609 more cases than it had in 2002 (1). Chlamydia cases are usually under-reported annually due to the fact that infected people do not know they are infected because they are asymptomatic (without symptoms) (3).  The U.S. National Health & Nutrition Exam Survey estimates that there are 2,291,000 cases of Chlamydia infections of non-institutionalized U.S. civilians in the 14 - 39 years old age group (3).


The World Health Organization (WHO) in 1999 estimated 92 million new cases of Chlamydia infections among adults globally (11). The following list details the estimated numbers of new Chlamydia infection cases per each region of the world in 1999 (11):


South & Southeast Asia - 43 million

Sub-Saharan Africa - 16 million

Latin America & Caribbean - 9.5 million

Eastern Europe & Central Asia - 6 million

East Asia & Pacific - 5.3 million

Western Europe - 5 million

North America - 4 million

North Africa & Middle East - 3 million

Australia & New Zealand - 340, 000

These are the most recent estimates as the WHO is currently developing new estimates to reflect up to 2005. These estimates were suppose to have been ready for publication late 2007, but are still under development (10).


Chlamydia’s names derives from the Greek work “chlamys” which means “ to drape around the shoulder” (8). This “cloaking” or “draping” describes the intracytoplasmic inclusion caused by the bacterium as it “ drapes” around the infected cell’s nucleus. C. trachomatis are considered nonmotile, obligate intracellular parasites. At one time they were considered viruses since they multiply in the cytoplasm of host cells. They are now classified as bacteria(5,8). C. trachomatis contain both DNA and RNA. They also has a cell wall which is similar to the cell wall of gram negative bacteria which contains ribosomes (5,8).  C. trachomatis has a limited host range. Infections are restricted to humans and one strain is responsible for mouse pneumonitis. C. trachomatis  is divided into 3 biovars. Trachoma, lymphogranuloma venereum (LGV), and a third biovar which contains mice pneumonitis agent.  The human biovars are divided into 15 serotypes which are also known as serovars. The serovars are based on antigenic differences among the strains. The three serovars for LGV are L1, L2, L3. The other 12 serovars are associated with the trachoma biovar. The serotypes B, and D through K are associated with oculogenital disease and pneumonias while serotypes A, B, Ba, and C are associated with blinding trachoma. C. trachoma is bacterium is found in two forms: elementary body (EB) and reticulate body (RB)(8,9). EB is the infectious form and it usually lies outside of cells. Receptors for EB are primarily epithelial cells (columnar, cubical, or transitional) which are found on the mucous membranes of the urethral tract, end cervix, endometrial, fallopian tubes, anorectum, respiratory tract, and conjunctiva (9). LGV strains infect reticuloendothelial cells of lymph tissues causing systemic infections. 


There are several test which aid in identifying C. trachomatis. The following is a list of the diagnostic tests for Chlamydia:

A. Nucleic Acid Amplification Test (NAAT) -

            1. C. trachomatis DNA, SDA - This test directly detects the presence of  Chlamydia DNA. The test can be performed on either swab or urine specimens collected from men or women. It can also be performed on endocervical specimens submitted in  a liquid-based PAP test vial. This test is based on strand displacement amplification (SDA) and is highly sensitive and specific. A positive DNA result is highly indicative of a Chlamydia infection (7).

            2.  C. trachomatis RNA, TMA - This test directly detects the presence of Chlamydia ribosomal RNA (rRNA). This test can be performed on either swab or urine specimens collected from men or women. It is based on transcription- mediated amplification (TMA). A positive TMA result is highly indicative of Chlamydia infection(7). 

B. Nucleic Acid Hybridization Test (Gen Probe) - This hybridization test directly detects presence of Chlamydia by using a DNA probe which is specific for the organism’s nucleic acid. This can be performed on swab specimens from men and women, but not on urine specimens. Positive results are automatically confirmed using organism specific probes (7).

C. Direct Fluorescent Antibody Assay (DFA) - DFA test directly detects the presence of Chlamydia. Swab slide specimens can be collected from men or women. These specimens can be from endocervical, urethral, conjuctival, rectal, or nasopharyngeal sources. The specimens are incubated with fluoroscein-labeled monoclonal antibody. They are observed and examined microscopically for            fluorescence of Chlamydia elementary bodies. A positive DFA indicates the presence of Chlamydia infection (7).

D. Enzyme Linked Immunosorbent Assay (ELISA) - This assay relies on the ability of   biological materials, such as antigens, to adsorb to plastic surfaces, such as   polystyrene (solid phase). When the antigens bound to the solid phase are brought into contact with a patient’s serum, antigen specific antibody, if it is present, will bind to the antigen on the solid phase, thus forming antigen-antibody complexes.     Presence of these antigen-antibody complexes are indicative of Chlamydia exposure. This serum test is helpful as additional information, providing evidence of exposure, but does not show correlation with infected status. Serum specimens are collected from men or women (4).

E.  C. trachomatis Culture - This culture detects the presence of C. trachomatis. The bacterium is grown in a cell culture and identified using immunofluorescence assay   with monoclonal antibodies specific for the major outer membrane protein (MOMP), which is present in all 15 known serovars of C. trachomatis. A positive culture is highly specific for Chlamydia infection. Cultures can be collected from   endocervical, urethral, conjuctival, nasopharyngeal, throat swabs, as well as from, biopsies, seminal, pleural, peritoneal fluids (7).


It is important to note that proper collection and handling of specimens is crucial to avoid false-positive and false-negative results. Sampling too soon after the end of a treatment therapy may cause for incorrect results in some of the tests available (7). Test of cure, if ordered, should be administered 3 weeks after therapy (2,7). Sexually transmitted disease screening and Chlamydia testing during annual physical exams and at onset of signs and symptoms using any of the tests aforementioned will aid in controlling Chlamydia exposure in a population. Also, use of condoms, though not 100% effective, can lessen the risk of exposure to Chlamydia. Abstinence is the most effective way of avoiding exposure to Chlamydia.


Signs and symptoms of Chlamydia infections can vary in men and women. Chlamydia is known as the “silent” disease because about three quarters of infected women and about one half of infected men have no symptoms(2). When symptoms do occur, they are usually 1 to 3 weeks after exposure . Women may present with abnormal vaginal discharge, dysuria (painful urination), pelvic pain, lower back pain, fever, nausea, pain during intercourse, irregular bleeding between menses. Even if the infection spreads from the cervix to the fallopian tubes women may still be asymptomatic (2). Chlamydia infections in the cervix can also spread to the rectum (2). Chlamydia infection symptoms in men differ from women. Men may present with penile discharge, dysuria, penile itching, testicular/scrotal swelling and pain. Rectal pain, discharge, or even bleeding may occur if the infections is in the rectum (2).


Identifying and diagnosing Chlamydia infections is important since this will determine which is the best course for treatment of the infection. C. trachomatis sensitive to antibiotics such as azithromycin, or doxycycline. A single dose of azithromycin or a week of doxycycline (taken twice daily) are the most commonly used treatments (2). Azithromycin can be used in pregnant women (2). Erythromycin orally (4 doses daily for 2 weeks), not topically, is the antibiotic of choice for conjuctival Chlamydia infections in newborns (). A very important part of the treatment plan is notification of sexual partners who must subsequently be treated to avoid all involved to be reinfected. Test of cure can be administered 3 weeks after therapy has ended if indicated (2,7).


Chlamydia infections, if not treated, can cause both short-term and long-term complications. If untreated in women it can spread into the fallopian tubes and cause pelvic inflammatory disease (PID) (2). PID can cause permanent damage to fallopian tubes, the uterus, and the surrounding tissues. The damage caused can lead to infertility, chronic pelvic pain, increase in risk for ectopic pregnancies. Increase exposure to Chlamydia can also increase the risk of becoming infected with HIV by up to five times. In pregnant women, untreated Chlamydia infections can lead to premature delivery. Babies born to infected women can get Chlamydia infections in their eyes or respiratory tracts. Chlamydia is the leading cause of newborn pneumonia and conjunctivitis. In men, complications may include epididymitis (swelling of the tube which carries sperm from testis), pain, fever, and rarely, sterility (2).


There is no vaccine to protect the population from Chlamydia infections. At this time there are laboratories, such as Rocky Mountain Laboratories (RML), who are actively working to develop a vaccine against C. trachomatis. Dr. Harlan Caldwell of RML and his research group are actively testing a vaccine that can protect against all 15 Chlamydia varieties. His group’s studies have shown that the vaccine can prevent lab cells from becoming infected. They are currently testing it in animals (6). Until a vaccine is developed though, abstinence, sexual education/prevention programs, and timely and proper screening for and treatment for Chlamydia are the only recourse in controlling this infection. 




1. Center for Disease Control. STD Surveillance 2006. Available from: Accessed February 9, 2008.


2. Center for Disease Control. STD Treatment Guidelines 2006. Available from: Accessed February 9, 2008.


3. Center for Disease Control. Chlamydia-CDC Fact Sheet. Available from: Accessed February 9, 2008.


4. Diagnostic Automation, Inc. Chlamydia IgG ELISA. Available from: Accessed February 16, 2008.


5. The Merck Manual of Diagnosis and Therapy. 16th ed. Merck Research Laboratories. Rahway, N.J. 1992.


6. Pekoc K. RML Vaccine Concept Awarded for Innovation. NIH News. June 11, 2007. Available from: Accessed February 7, 2008.


7. Quest Diagnostics. December 2007. Prevention of Pelvic Inflammatory Disease (PID) - Screening for Chlamydia trachomatis and Neisseria gonorrheae. Available from: Accessed February 11, 2008.


8. TJ Clark Co. Chlamydia Trachomatis. Available from:  Accessed February 11, 2008.


9. The World Health Organization. Chlamydia Trachomatis. Available from: Accessed February 25, 2008.


10. The World Health Organization. Sexually Transmitted Infections. Available from: Accessed February 25, 2008.


11. The World Health Organization. Global Prevalence & Incidence of Selected Curable Sexually Transmitted Infections.  Accessed February 25, 2008.