Chlamydia

Overview

Chlamydia is a common sexually transmitted infection (STI) caused by the bacterium Chlamydia trachomatis that can occur in both men and women. It is easily treated and cured with antibiotics.

Disease epidemiology

Globally, it is the most common STI. The global prevalence among people aged 15 to 49 years was estimated to be 4.0% for women and 2.5% for men in 2020. Chlamydia genital infections occur frequently among sexually active adolescents and young adults.

In Singapore, chlamydia had the highest incidence, followed by syphilis and gonorrhoea, among the three notifiable STIs in 2019 and 2020. It was more commonly reported in men.

Pathogen(s)

Chlamydia trachomatis.

Transmission

Chlamydia can be transmitted through vaginal, anal, or oral intercourse with an infected individual. Semen does not have to be present to be infected with or spread the infection. Sexually active teenage girls and young women are more prone to develop chlamydial infection as the opening of the uterus (cervix) is not fully matured.

An infected mother can also transmit chlamydia to her baby during vaginal delivery.

Incubation period: The incubation period is poorly defined but is probably 5 to 14 days or longer.

Infectious period: Unknown but is presumed to last until treatment is completed. If untreated, it may persist for several months.

Clinical features

Many adult genital infections and most pharyngeal and rectal infections caused by chlamydia are asymptomatic. Chlamydia often does not cause symptoms especially in women. If symptoms do occur, they are usually mild and start to show between one to three weeks after exposure to the bacteria.

In women, symptoms may include:

• Abnormal vaginal discharge

• Bleeding between menstrual periods or after sex

• Pelvic pain

• Burning sensation when urinating

In men, symptoms may include:

• Burning when urinating

• Discharge from the penis

• Pain or discomfort in the testicles

Anal infection in women and men can cause:

• Pain

• Discharge

• Bleeding

Serotypes L1–L3 Chlamydia trachomatis can cause another STI called lymphogranuloma venereum. The symptoms of this infection include genital sores followed by fever and swelling of the lymph nodes in the groin.

Several important complications may result from chlamydia infections, including:

• Pelvic inflammatory disease

• Ectopic pregnancy and tubal infertility in women

• Epididymo-orchitis in males

• Conjunctivitis and reactive arthritis in both sexes

Maternal-foetal transmission to newborns during delivery may lead to neonatal conjunctivitis and pneumonia.

Risk factors

Risk factors include:

• Unprotected sex with an infected person

• Having multiple sex partners

• Inconsistent condom use

• Persons who exchange sex for money or drugs

• History or current presence of other STIs

Diagnosis

Tests for diagnosis include:

• Nucleic acid-based amplification testing (NAAT), a gold standard.

  • For females, cervical or vulvo-vaginal swabs are specimens of choice, followed by first void urine (FVU)

  • For males, urine is the specimen of choice; FVU is as sensitive as urethral swabs

• Polymerase chain reaction (PCR) can be used to test a range of specimens (urine, urethral, cervical, rectal, pharyngeal).

Treatment and management

Recommended regimens for uncomplicated chlamydia infections in adults:

• Doxycycline 100mg orally 2 times a day, for 7 days

Recommended regimens for chlamydia infections in pregnancy:

• Azithromycin 1g orally, single dose

Follow-up:

• A test-of-cure is not necessary if the patient had complied to and completed tetracycline or azithromycin treatment, unless symptoms persist or a reinfection is suspected.

• Test-of-cure is however recommended after 4 weeks of infection in infants, children and pregnant women, or when erythromycin was used.

• Non-culture tests (e.g., NAATs) performed within 4 weeks of completing treatment may yield false positive tests due to persistence of chlamydia antigens.

• Repeat infection in females may lead to increased risk of complications. Rescreening for reinfection 3 to 4 months after the initial infection may be required, especially for females with high-risk of infection.

• Serologic tests for syphilis and HIV should be performed during the follow-up; if negative, they should be repeated at three months after the last high-risk exposure.

Refer to the Department of Sexually Transmitted Infections Control (DSC)'s website for more information on alternative regimens.

Precaution, prevention, and control

Annual screening for chlamydia symptoms and other STIs is recommended for all individuals who are sexually active.

• Individuals with multiple sex partners, change in sex partner, or engaging in unprotected sex should consider regular screening

• More frequent screening than annual might be indicated for certain individuals based on their risk behaviours

Prevention of chlamydia includes:

• Consistent and correct use of condoms when engaging in sexual activity

• Limit the number of sex partners

• Get tested for STIs regularly

Management of sexual contacts:

Sex partners of symptomatic male patients within the last 60 days from symptom onset (or the most recent sex partner if the last contact was more than 60 days) should be screened and treated for chlamydial infection epidemiologically. The lookback period for contacts of female patients and asymptomatic males is longer, e.g., 3 months.

Notification

Chlamydial genital infection is a notifiable disease.

Who should notify:

• Medical practitioners

• Laboratories

When to notify:

• Medical practitioners – on clinical suspicion

• Laboratories – on laboratory confirmation

How to notify:

• Please refer to the Infectious Disease Notifications for more information.

Notification timeline:

• Within 72 hours from time of diagnosis.

Resources

Refer to Resources for communicable disease surveillance in Singapore.

Refer to DSC’s website for more information about alternative regimens.

References

• Centers for Disease Control and Prevention. STI treatment guidelines: Chlamydial infections. 2021

• Department of Sexually Transmitted Infections Control (DSC). STI management guidelines 7^th edition. 2021

• World Health Organization. Chlamydia. 2023