Chlamydia

C. trachomatis has 18 immunologically defined serovars:

In the United States, C. trachomatis is the most common bacterial cause of STIs, including

Maternal transmission of C. trachomatis causes neonatal conjunctivitis Neonatal Conjunctivitis Neonatal conjunctivitis is watery or purulent ocular drainage due to a chemical irritant or a pathogenic organism. Prevention with antigonococcal topical treatment at birth is routine. Diagnosis... read more and neonatal pneumonia Neonatal Pneumonia Neonatal pneumonia is lung infection in a neonate. Onset may be within hours of birth and part of a generalized sepsis syndrome or after 7 days and confined to the lungs. Signs may be limited... read more . Universal prenatal screening and treatment of pregnant women have greatly reduced the incidence of infant C. trachomatis infection in the United States (1 General reference Three species of Chlamydia cause human disease, including sexually transmitted infections and respiratory infections. Diagnosis depends on species; culture, nucleic acid amplification... read more ).

The organism can be isolated from the rectum and throat in adults (usually in men who have sex with men [MSM]). Rectal infection with L2 strains can cause severe proctocolitis that can mimic acute inflammatory bowel disease in MSM who are HIV-positive.

C. pneumoniae can cause pneumonia (especially in children and young adults) that may be clinically indistinguishable from pneumonia caused by Mycoplasma pneumoniae. In some patients with C. pneumoniae, pneumonia, hoarseness, and sore throat may precede coughing, which may be persistent and complicated by bronchospasm.

Approximately 6 to 19% of community-acquired pneumonia Community-Acquired Pneumonia Community-acquired pneumonia is defined as pneumonia that is acquired outside the hospital. The most commonly identified pathogens are Streptococcus pneumoniae, Haemophilus influenzae... read more cases are due to C. pneumoniae. Outbreaks of C. pneumoniae pneumonia pose a particular risk for people in congregate settings (eg, nursing homes, schools, military installations, prisons). No seasonal variations in occurrence have been observed.

C. pneumoniae has also been implicated as an infectious trigger of reactive airway disease.

(See also the Centers for Disease Control and Prevention's [CDC] Psittacosis: For Clinicians and Laboratorians.)

C. psittaci causes psittacosis. Strains causing human disease are usually acquired from psittacine birds (eg, parrots), causing a disease characterized by pneumonitis. Patients may have severe headache and abnormal liver blood tests.

Psittacosis is a rare infection. Since 2010, typically < 10 cases/year are reported to the CDC (see also the CDC's Psittacosis). However, psittacosis might be underdiagnosed because mild cases do happen. History of epidemiologic exposure is very important, eg, pet bird owners, veterinarians, and workers in the poultry industry. Outbreaks have occurred among workers who handle turkeys and ducks in poultry processing plants.

(See also the CDC's 2021 Sexually Transmitted Infections Treatment Guidelines: Chlamydial Infections.)

C. trachomatis STIs are best identified in genital samples using nucleic acid amplification tests (NAATs) because these tests are more sensitive than cell culture and have less stringent sample handling requirements. Currently, NAATs are available for testing genital and urine specimens from adults and adolescents. NAATs for genital infection can be done using urine or vaginal swabs obtained by the patient or clinician. Several commercially available NAATs have been approved for extragenital infections (eg, those in the rectum or pharynx).

Serologic tests are of limited value except for diagnosing lymphogranuloma venereum and psittacosis.

C. pneumoniae is diagnosed by culture of respiratory tract specimens or by NAAT testing. Two NAATs for C. pneumoniae are available as part of panels that simultaneously test for multiple respiratory pathogens.

A primary clue to the diagnosis of C. psittaci infection is close contact with birds, typically pet birds such as parrots or parakeets, including veterinarians and workers in turkey and duck processing plants. Diagnosis is confirmed by serologic tests. Culture is not generally available. There are no commercially available NAATs for C. psittaci, but PCR can be done by the Centers for Disease Control and Prevention (CDC) and some specialty laboratories. (See also the CDC's different methods for diagnosing psittacosis.)

Doxycycline 100 mg orally 2 times a day for 7 days is the recommended treatment for urogenital chlamydia in adolescents and adults who are not pregnant (1 Treatment references Three species of Chlamydia cause human disease, including sexually transmitted infections and respiratory infections. Diagnosis depends on species; culture, nucleic acid amplification... read more ). A review of randomized trials that compared doxycycline and azithromycin for treating urogenital chlamydial infection found that microbiologic treatment failure among men was higher for azithromycin than for doxycycline (2 Treatment references Three species of Chlamydia cause human disease, including sexually transmitted infections and respiratory infections. Diagnosis depends on species; culture, nucleic acid amplification... read more ). The recommendation also is based on studies that showed a 7-day course of doxycycline was superior to a single dose of azithromycin for treatment of rectal infection in men who have sex with men (3 Treatment references Three species of Chlamydia cause human disease, including sexually transmitted infections and respiratory infections. Diagnosis depends on species; culture, nucleic acid amplification... read more ). The recommendations for use of doxycycline were expanded to include women because rectal infection is not routinely screened for in this population.

A single dose of azithromycin 1 g orally is an alternative treatment option. Azithromycin may be useful in populations that may have problems with compliance and may not be able to tolerate a 7-day course of multidose doxycycline.

Pregnant women can be given only a single dose of azithromycin 1 g orally.

Current sex partners should be treated. Patients should abstain from sexual intercourse until they and their partners have been treated for ≥ 1 week.

When gonorrhea Gonorrhea Gonorrhea is caused by the bacterium Neisseria gonorrhoeae. It typically infects epithelia of the urethra, cervix, rectum, pharynx, or conjunctivae, causing irritation or pain and purulent... read more is present and chlamydial infection has not been excluded (uncommon, because all currently available NAATs for gonococcal infection are duplexed with a test for C. trachomatis), concurrent treatment for gonorrhea Treatment Gonorrhea is caused by the bacterium Neisseria gonorrhoeae. It typically infects epithelia of the urethra, cervix, rectum, pharynx, or conjunctivae, causing irritation or pain and purulent... read more is recommended.

Screening and treatment of pregnant women is the most effective way to prevent neonatal chlamydial infection, including conjunctivitis and pneumonia. Neonatal ocular prophylaxis with erythromycin or other preparations does not prevent neonatal chlamydial conjunctivitis.

Azithromycin and doxycycline are first-line antibiotics for treatment of C. pneumoniae and psittacosis.

Specific infections are discussed elsewhere in THE MANUAL: Lymphogranuloma venereum Lymphogranuloma Venereum (LGV) Lymphogranuloma venereum (LGV) is a disease caused by 3 unique strains of Chlamydia trachomatis and characterized by a small, often asymptomatic skin lesion, followed by regional lymphadenopathy... read more and urethritis, pelvic inflammatory disease Pelvic Inflammatory Disease (PID) Pelvic inflammatory disease (PID) is a polymicrobial infection of the upper female genital tract: the cervix, uterus, fallopian tubes, and ovaries; abscess may occur. PID may be caused by sexually... read more , epididymitis Epididymitis Epididymitis is inflammation of the epididymis, occasionally accompanied by inflammation of the testis (epididymo-orchitis). Scrotal pain and swelling usually occur unilaterally. Diagnosis is... read more , reactive arthritis Reactive Arthritis Reactive arthritis is an acute spondyloarthropathy that often seems precipitated by an infection, usually genitourinary or gastrointestinal. Common manifestations include asymmetric arthritis... read more , neonatal conjunctivitis Neonatal Conjunctivitis Neonatal conjunctivitis is watery or purulent ocular drainage due to a chemical irritant or a pathogenic organism. Prevention with antigonococcal topical treatment at birth is routine. Diagnosis... read more and neonatal pneumonia Neonatal Pneumonia Neonatal pneumonia is lung infection in a neonate. Onset may be within hours of birth and part of a generalized sepsis syndrome or after 7 days and confined to the lungs. Signs may be limited... read more , trachoma Trachoma Trachoma is a chronic conjunctivitis caused by Chlamydia trachomatis and is characterized by progressive exacerbations and remissions. It is the leading cause of preventable blindness... read more , and inclusion conjunctivitis Adult Inclusion Conjunctivitis Adult inclusion conjunctivitis is caused by sexually transmitted Chlamydia trachomatis. Symptoms include chronic unilateral hyperemia and mucopurulent discharge. Diagnosis is clinical... read more .

The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.