Medically reviewed by: Stephanie Curreli, MD, PhD
Last Updated: Mar 1, 2019


Chlamydia is a sexually transmitted bacterial infection and the most common sexually transmitted disease (STD) in the United States with 2.8 million new cases annually. It affects both men and women and can spread via oral, vaginal or rectal intercourse. An infection may not always produce symptoms, which is why routine screening for chlamydia is recommended for at-risk sexually active men and women.

Chlamydia is easily treated with antibiotics. However, it can lead to serious reproductive health problems if left untreated. Pregnant women carry the risk of passing on the infection to their newborn.

Causes and Risk Factors

Chlamydia trachomatis is the species of bacteria that causes chlamydia. The route of transmission is through unprotected sexual contact (oral, vaginal and rectal) with an infected individual. The risk of infection is higher in individuals who are under the age of 25; engage in unprotected sexual contact; have multiple sexual partners; and/or have a prior history of STDs.

pap smear of chlamydia


The symptoms of chlamydia are often mild and therefore hard to notice. Symptoms may become noticeable 1-3 weeks following infection and include:

Diagnosis and Treatment

Laboratory tests that detect the chlamydia bacteria are the best way to diagnose the disease. The Centers for Disease Control and Prevention recommends routine screening for pregnant women and women under the age of 25 who are sexually active.

Chlamydia can be treated and fully cured with antibiotics such as azithromycin or doxycycline. The infection is cleared within 1-2 weeks of starting treatment, during which time it is important to abstain from sexual activity in order to prevent disease transmission. If left untreated, chlamydia can spread to the uterus and fallopian tubes in women and cause pelvic inflammatory disease (PID) - a serious condition that can result in permanent scarring and infertility. In men, the infection can spread to the epididymis and prostate gland, causing pain and fever. Infected women who are pregnant may pass the disease to their newborn during childbirth.


The best way to prevent chlamydia is by practicing abstinence or maintaining a monogamous sexual relationship with a non-infected partner. Correct use of condoms during both vaginal and rectal intercourse helps reduce the risk of contracting chlamydia and other STDs. All sexually active women under the age of 25 should seek routine screening for early detection and treatment of chlamydia. Pregnant women receive routine screening for chlamydia as part of prenatal testing. Individuals with a previous history of chlamydia can become reinfected and should continue to practice these preventative measures.


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Tina Shahian, PhD

Tina is a Life Science Writer for a number of online publications, including Her expertise is in conveying complex scientific topics to diverse audiences. Tina earned her PhD in Biochemistry from the University of California, San Francisco and her BS degree in Cell Biology from U.C. Davis. In her spare time, she enjoys drawing science-related cartoons.