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Chlamydia, caused by the bacterium Chlamydia trachomatis, remains the most commonly reported bacterial infection in the United States and the most prevalent sexually transmitted infection worldwide. Rising global rates, frequent asymptomatic presentation, and the wide spectrum of associated diseases—including cervicitis, urethritis, pelvic inflammatory disease, epididymitis, proctitis, neonatal conjunctivitis, and trachoma—underscore its public health impact. This course reviews the distinct serovars that correlate with varied clinical syndromes, timely diagnosis through nucleic acid amplification testing, appropriate antimicrobial therapy, partner management, and follow-up testing, which are essential to preventing complications such as infertility, ectopic pregnancy, chronic pelvic pain, and adverse neonatal outcomes. This activity explores the epidemiology, clinical manifestations, diagnostic strategies, and evidence-based treatment of C trachomatis. Participants should expect to strengthen diagnostic accuracy, improve therapeutic decision-making, enhance screening and counseling practices, and optimize interprofessional coordination. This activity for healthcare professionals is designed to enhance the learner's competence in identifying chlamydia infections, performing the recommended evaluation, applying current guidelines, and implementing an appropriate interprofessional approach when managing this condition to reduce transmission, prevent long-term sequelae, and deliver safer, more comprehensive patient-centered care. Objectives: Screen high risk patients for Chlamydia trachomatis according to current guidelines. Identify patients with symptoms consistent with Chlamydia trachomatis infections. Select appropriate antibiotics to treat Chlamydia trachomatis infections. Coordinate with the interprofessional team to ensure appropriate management of patients with Chlamydia trachomatis infections. Access free multiple choice questions on this topic.

Chlamydia is a sexually transmitted infectious disease caused by the bacterium Chlamydia trachomatis. In the United States, chlamydia is the most commonly reported bacterial infection.[1] Globally, Chlamydia trachomatis is the most common sexually transmitted infection (STI), and reported rates of infection have been climbing in the last few decades.[2] C trachomatis causes the ocular infection trachoma, which is the leading infectious cause of blindness worldwide.[3] In females, the cervix is the most commonly infected anatomic site. This can manifest as cervicitis, urethritis, pelvic inflammatory disease, perihepatitis, or proctitis. Chlamydial infections in women, especially if untreated, increase the risk of infertility and ectopic pregnancy, leading to high medical costs.[4] Associated risks of chlamydia infection during pregnancy are also present. Additionally, infants born vaginally to mothers infected with genital Chlamydia trachomatis may develop conjunctivitis or pneumonia. In men, infection with Chlamydia trachomatis can lead to urethritis, epididymitis, prostatitis, proctitis, or reactive arthritis. Both men and women infected with C trachomatis may also experience conjunctivitis, pharyngitis, and lymphogranuloma venereum (see Image. Follicular Conjunctivitis). Lymphogranuloma venereum (LGV), caused by distinct serovars of Chlamydia trachomatis, is a less common disease characterized by enlarged lymph nodes or severe proctocolitis.[5]

Chlamydia trachomatis is a gram-negative, anaerobic, intracellular obligate bacterium that replicates within eukaryotic cells.[6] C trachomatis differentiates into 18 serovars (serologically variant strains) based on monoclonal antibody-based typing assays. These serovars correlate with multiple medical conditions as follows: Serovars A, B, Ba, and C: Trachoma (a serious ocular illness endemic in Africa and Asia) [3] Serovars D-K: Genital tract infections and neonatal infections Serovars L1-L3: LGV, which correlates with genital ulcer disease in tropical countries [7]

Urogenital chlamydia infections are the most commonly reported bacterial infections in the United States and the most common cause of STIs in the world.[1][2] The overall rate of urogenital infection amongst United States women is roughly 2 times that of United States men, with a higher prevalence in people 15 to 24 years of age.[8] Epidemiological evidence strongly links lower socioeconomic status with a higher risk of Chlamydia trachomatis infection.[9] A recent study found higher rates of repeat chlamydia positivity more than 30 days but less than 365 days after a previous positive test among people of Black race, 13 to 19 years of age, and with a history of prior STI.[10]

Chlamydia is unique among bacteria, possessing an infectious cycle and 2 developmental forms: the infectious form, known as the elementary body, and the reticulate body. The elementary body is metabolically inactive and is taken up by host cells. Within the host cell, the elementary body will differentiate into the metabolically active reticulate body. The reticulate body will then use host energy sources and amino acids to replicate and form a new elementary body, which can then infect additional cells.[6] C trachomatis targets the squamocolumnar epithelial cells of the endocervix and upper genital tract in women, and the conjunctiva, urethra, and rectum in both men and women.[11] The bacterium is transmitted through direct contact with infected tissue, including vaginal, anal, or oral sex, and can even be passed from an infected mother to the newborn during childbirth.[11]

Typical intracytoplasmic inclusions and free chlamydiae are identifiable in Giemsa-stained cell scrapings. Stained conjunctival scrapings are positive in 90% of infants with neonatal conjunctivitis and 50% of adults with inclusion conjunctivitis.[12] Cytology techniques can be used to evaluate endocervical scrapings; however, their sensitivity and specificity are low.[13]

C trachomatis can lead to many urogenital infections, including cervicitis, pelvic inflammatory disease, urethritis, epididymitis, prostatitis, and lymphogranuloma venereum.[14] Extragenital infections caused by C trachomatis include conjunctivitis, perihepatitis, pharyngitis, reactive arthritis, and proctitis (see Image. Alpha-1 Antitrypsin Deficiency in Emphysema). More frequently, patients remain asymptomatic reservoirs of the disease. In the minority of patients who become symptomatic, clinical signs depend on the location of the infection. Below are the common signs and symptoms associated with C trachomatis urogenital infections. Cervicitis: Over 80% of women will be asymptomatic or have mild symptoms, eg, vaginal discharge, bleeding, abdominal pain, and dysuria.[15] Only a minority of women have the classic presentation of mucopurulent cervicitis with discharge and easily induced endocervical bleeding. Some women may complain of postcoital bleeding or intermenstrual bleeding. Pelvic inflammatory disease (PID): This occurs when C trachomatis ascends to the upper reproductive tract. Most commonly, these patients will have abdominal or pelvic pain with or without signs and symptoms of cervicitis. Other symptoms include nausea, vomiting, fevers, chills, low back pain, pain with intercourse, dysuria, or postcoital bleeding.[16] Urethritis: This condition is most commonly seen in men. Subtle clinical differences between gonococcal urethritis and chlamydial urethritis exist, but making a reliable distinction without testing is not possible. Urethritis presents with dysuria and urethral discharge, which is typically white, gray, or sometimes clear, and may only be evident after penile "stripping" or during morning hours. Women with urethritis may complain of frequency or dysuria and may mistake their symptoms for a urinary tract infection. Urinalysis will reveal pyuria, but neither bacterial culture nor Gram stain will reveal organisms.[14]

Urethritis: This condition is most commonly seen in men. Subtle clinical differences between gonococcal urethritis and chlamydial urethritis exist, but making a reliable distinction without testing is not possible. Urethritis presents with dysuria and urethral discharge, which is typically white, gray, or sometimes clear, and may only be evident after penile "stripping" or during morning hours. Women with urethritis may complain of frequency or dysuria and may mistake their symptoms for a urinary tract infection. Urinalysis will reveal pyuria, but neither bacterial culture nor Gram stain will reveal organisms.[14] Perihepatitis: Also known as Fitz-Hugh-Curtis syndrome, this syndrome occurs when a chlamydia infection leads to inflammation of the liver capsule and the surrounding peritoneal surfaces. This syndrome is most commonly seen in patients who have a pelvic inflammatory disease, and perihepatitis is associated with right upper quadrant or pleuritic pain. Unlike other conditions that may affect the liver or cause right upper quadrant pain, abnormalities in liver enzymes are not typically found.[17] Epididymitis: Typically, men will present with unilateral testicular pain and tenderness, possible hydrocele, palpable swelling of the epididymis, and fever.[11] Proctitis: Rectal infection with chlamydia can be asymptomatic if caused by genital serovars D through K. However, if LGV serovars L1-L3 are the cause of proctitis, patients may complain of rectal pain, discharge, and bleeding in the setting of receptive anal intercourse. Patients may also present with a fever or malaise. This is seen almost exclusively in males who have sex with males; however, anal intercourse is not uncommon in heterosexual intercourse.[11] Prostatitis: Symptoms include dysuria, urinary dysfunction, pelvic pain, and pain with ejaculation.[18] Expressed prostatic secretions may reveal increased leukocyte counts on microscopy. Reactive arthritis: Approximately 1% of men with urethritis due to chlamydial infection also develop reactive arthritis, and a third will have the reactive arthritis triad of arthritis, urethritis, and uveitis, formerly known as Reiter syndrome.[19]

Prostatitis: Symptoms include dysuria, urinary dysfunction, pelvic pain, and pain with ejaculation.[18] Expressed prostatic secretions may reveal increased leukocyte counts on microscopy. Reactive arthritis: Approximately 1% of men with urethritis due to chlamydial infection also develop reactive arthritis, and a third will have the reactive arthritis triad of arthritis, urethritis, and uveitis, formerly known as Reiter syndrome.[19] Conjunctivitis: Direct inoculation with genital secretions containing C trachomatis serovars can lead to conjunctival infection. Symptoms typically include nonpurulent conjunctivitis (erythematous injection of the surface epithelium). The conjunctiva may have a cobbled appearance. Conjunctivitis is the most common manifestation of chlamydial infection in newborns.[20] Pneumonia: Infants born to mothers who have a cervical infection with C trachomatis may develop pneumonia 5% to 30% of the time.[21] Recognition usually occurs between 4 to 12 weeks of age, though almost all infants have symptoms before 8 weeks. Nasal congestion and cough are common, and some infants may have thick nasal secretions.[22] Infants usually have no fever or only a minimal fever; they may have tachypnea, and they may have a characteristic paroxysmal staccato cough. In preterm infants, apneic spells may be seen. Rales may be heard on auscultation of the lungs, but wheezing is uncommon. Pharyngitis: Although C trachomatis is not typically considered a significant cause of pharyngitis, it can be detected in the pharynx via nucleic acid amplification tests. Lymphogranuloma venereum: Patients will present with painless genital ulcers. The ulcers typically have a small, stellate appearance. The development of inguinal lymphadenopathy typically follows the appearance of ulcers.

Among C trachomatis infections, trachoma is the only infection which is diagnosed clinically. Other chlamydial infections with specific clinical syndromes require laboratory confirmation. The gold standard for the diagnosis of urogenital chlamydia infections is nucleic acid amplification testing (NAAT). The preferred method for testing is via vaginal swabs for females or the first-catch urine for males. Urine can be used for females, however it may be less sensitive. Testing can also be performed on endocervical or urethral swabs. Swabs should have a wire or plastic shaft; the tip should be dacron or rayon, or a cytobrush. Other materials may inhibit Chlamydia trachomatis. Alternative methods of testing include culture, rapid testing, serology, antigen detection, and genetic probes. If no testing is available, treatment is recommended based on clinical presentation.[14] When a patient presents with suspected chlamydia infection, a workup for other STDs should be carried out. A complete blood count is essential if PID is suspected. One may consider testing for HIV, gonorrhea, and syphilis. The sexual partner must be tested for chlamydia.[23] A pregnancy test should be performed, as pregnancy is a contraindication to doxycycline therapy.[24] Additionally, cytology is often used in patients with conjunctivitis and ocular trachoma. Cultures are usually not done for chlamydia as the organism is difficult to grow in the laboratory. However, in patients with anal and rectal involvement, cultures are ideal as other tests are difficult to interpret. The United States Preventive Services Task Force (USPSTF) recommends regular screening for chlamydia in all sexually active women 24 years or younger and in women 25 years and older who are at increased risk of infection because, if left untreated, the infection is associated with PID, infertility, and chronic pelvic pain.[25] In males, the leucocyte esterase test in urine is diagnostic for gonorrhea or chlamydia in the absence of a urinary tract infection.[23]

The goal of treatment is to prevent complications associated with infection (eg, PID, infertility), decrease the risk of transmission, and resolve symptoms. Treatment for uncomplicated urogenital chlamydia infection is with doxycycline or azithromycin.[23] A 2019 Cochrane review found that azithromycin had higher microbiological failure rates than doxycycline, but little to no difference in risk of clinical failure.[26] However, directly observed single-dose azithromycin therapy may be preferred to doxycycline when nonadherence is a substantial concern.[23] Levofloxacin is an alternative option. Chlamydial infection and gonococcal infections often coexist. In men, the combined treatment for urogenital gonococcal infection should be based on the detection of the organism by NAAT or Gram stain. In women, the Gram stain is less helpful because of the possibility of colonization by typical Neisseria species within the vaginal flora. Therefore, combined treatment should be dependent on a patient's individual risk and local prevalence rates.[23] Patients should have partners identified and tested. They should also be counseled on high-risk behaviors, avoid sexual activity for 1 week after initiating therapy, and consider testing for HIV. Doxycycline has also been recommended for postexposure prophylaxis in appropriate populations.[27] Verification of cure should occur 3 weeks after treatment completion, and retesting should be performed 3 months after treatment.[23] If symptoms persist after treatment, consider secondary bacterium coinfection versus reinfection. Follow-up culture is not recommended for most people, but may be considered in pregnant females.[28]

Because Chlamydia trachomatis can lead to a broad spectrum of clinical diseases or manifestations, the differential diagnosis of various presenting complaints is also broad. Clinicians should consider other etiologies that may affect each body area or organ system and may manifest similarly, including: Dysuria Gonorrhea Genital herpes Urinary tract infection Abdominal pain Appendicitis Cholecystitis Constipation Pelvic pain Endometriosis Ovarian cysts Adenomyosis Vaginal discharge Bacterial vaginosis Trichomonas vaginalis Gonorrhea Vaginal candidiasis Foreign body Mycoplasma genitalium infection Ureaplasma infection Rectal discharge Inflammatory bowel disease Gonorrhea Conjunctivitis Viral infection Allergy Gonococcal infection Postcoital or intermenstrual bleeding Cervical cancer Cervical or endometrial polyp Cervical ectropion Leiomyoma Pregnancy Genital ulceration Herpes simplex Syphilis Chancroid Granuloma inguinale

Antibiotic treatment has a 95% effectiveness rate for first-time therapy. The prognosis is excellent when treatment is initiated promptly and the entire course of antibiotics is completed. Although treatment failures with primary therapies are quite rare, reinfection is common and is usually related to the nontreatment of infected sexual partners or acquisition from a new partner. Death is rare but can be caused by progression to salpingitis and tubo-ovarian abscess with rupture and peritonitis. The most significant morbidity occurs with repetitive infection with chlamydiae, which leads to scarring of the fallopian tubes and subsequent sterility.[30]

PID places women of childbearing age at increased risk for ectopic pregnancy. Inflammation and scarring within the upper genital tract may impair fertility or contribute to chronic pelvic pain. Chlamydial infection during pregnancy also elevates the likelihood of prelabour rupture of membranes (PROM), premature prelabour rupture of membranes (PPROM), and preterm delivery.[31]

Chlamydia trachomatis infection frequently progresses without symptoms, yet undiagnosed or untreated disease can lead to significant reproductive and systemic complications. Routine screening helps detect silent infection and prevent sequelae such as pelvic inflammatory disease, infertility, ectopic pregnancy, and adverse pregnancy outcomes. Annual screening is recommended for all sexually active females younger than 25, with targeted screening for older women at increased risk, men who have sex with men, individuals with HIV, and specific age groups entering correctional facilities. Because C trachomatis is a notifiable infection, timely reporting, partner notification, and appropriate treatment remain essential components of public health management.[25] Effective care relies on coordinated efforts across the healthcare team. Physicians, general practitioners, advanced practitioners, nurses, and pharmacists must apply strong clinical assessment skills, evidence-based screening strategies, and clear patient education to support early detection and treatment. Interprofessional communication ensures accurate reporting, streamlined partner management, and consistent follow-up. Collaborative workflows strengthen patient-centered care by reducing barriers to screening, supporting adherence to therapy, and improving safety through timely diagnosis and prevention of complications. This shared approach promotes better outcomes, enhances team performance, and reinforces trust and engagement throughout the continuum of care.

Chlamydia trachomatis infection frequently progresses without symptoms, yet undiagnosed or untreated disease can lead to significant reproductive and systemic complications. Routine screening helps detect silent infection and prevent sequelae such as pelvic inflammatory disease, infertility, ectopic pregnancy, and adverse pregnancy outcomes. Annual screening is recommended for all sexually active females younger than 25, with targeted screening for older women at increased risk, men who have sex with men, individuals with HIV, and specific age groups entering correctional facilities. Because C trachomatis is a notifiable infection, timely reporting, partner notification, and appropriate treatment remain essential components of public health management. Effective care relies on coordinated efforts across the healthcare team. Physicians, general practitioners, advanced practitioners, nurses, and pharmacists must apply strong clinical assessment skills, evidence-based screening strategies, and clear patient education to support early detection and treatment. Interprofessional communication ensures accurate reporting, streamlined partner management, and consistent follow-up. Primary care practitioners should educate patients on the importance of using a condom during sex, practicing safe sex, or abstaining from sexual activity to prevent chlamydia. Pharmacists should verify dosing and agent selection for antimicrobial therapy, check for drug interactions, and report any concerns to the prescriber. This approach results in decreased incidence and improved outcomes. Collaborative workflows strengthen patient-centered care by reducing barriers to screening, supporting adherence to therapy, and improving safety through timely diagnosis and prevention of complications.