What is chlamydia?
Chlamydia infection is a sexually transmitted infection (STI) caused by the bacteria
Chlamydia trachomatis.

How common is chlamydia?
Chlamydia infection is the most common bacterial STI. In 2013, there were over 1.4 million cases of Chlamydia reported. According to the most recent estimates, 15–24 year-old females continue to have higher rates of Chlamydia than any other age-sex group. In men, the highest rates of reported chlamydia infections are among 20-24 year olds.1
How is chlamydia spread?
Chlamydia infection can be spread through vaginal, anal, or oral sex. It can also be spread from an infected mother to her baby at delivery and cause an eye or lung infection.

Does chlamydia cause symptoms?
Most of the time, a chlamydia infection does not cause symptoms. About 90% of females and 85% of males have no symptoms from a chlamydia infection.2 Since so few people have symptoms of the infection, they do not know that they have an STI and do not go to the doctor to be treated. Without symptoms, infected people can spread the chlamydia infection to their sexual partners without knowing it. Infected males who remain untreated frequently re-infect their female partners.
Because this infection does not usually cause symptoms, the U.S. Preventive Services
Task Force recommends that all sexually active females aged 24 and younger undergo screening for chlamydia infection.3,4 The CDC also recommends that sexually active women aged 25 or younger, pregnant women, as well as older women with a new sex partner or multiple sex partners, are screened at least once every year.5
What are the symptoms of chlamydia?
Some people do get symptoms when they have a chlamydia infection. Symptoms of chlamydia include painful urination and discharge from the penis or vagina. If the chlamydia infection involves the anus and rectum, pain and bleeding of the rectum may occur.

Are there any treatments available for chlamydia?
Chlamydia infection is curable with antibiotics. However, many infections go unrecognized for long periods of time because the infected person does not have symptoms. If a chlamydia infection causes damage to a person’s body before antibiotic treatment is started, that damage may be permanent.

What complications can result from chlamydia?
One potential complication of chlamydia infection in a female is pelvic inflammatory disease (PID). If the chlamydia infection spreads from the cervix up into the uterus and fallopian tubes, PID can develop. PID may cause permanent damage in the fallopian tubes and scarring in the pelvic area. This damage to the fallopian tubes and scarring in the pelvis increases the chances that a woman will experience infertility, ectopic pregnancy, and chronic pelvic pain.
Another possible complication of chlamydia infection is the spread of the infection from a mother to her baby. If a mother has an active chlamydia infection at the time of delivery, the infant may develop a chlamydia infection in the eyes or lungs.

Does chlamydia affect the spread of HIV?
When a person has an active chlamydia infection, they are more likely to acquire HIV from a sexual partner. Chlamydia infection may increase the chances of getting HIV.6
Among men who have sex with men repeated chlamydial or gonorrheal infections increases the risk of HIV by about 8 times.7

Can chlamydia be prevented?
Yes; chlamydia can be prevented by refraining from sexual activity until a person is in a lifelong, mutually monogamous relationship with an uninfected partner. Mothers should be screened for chlamydia infection during pregnancy to prevent the spread of chlamydia infection to their babies.


This is an image of a normal cervix. This picture was kindly provided by W. David Hager, MD, FACOG, of the Women’s Care Center in Lexington, KY.


This is an image of a cervix affected by chlamydia. Pus and inflammation are present. This picture was kindly provided by W. David Hager, MD, FACOG, of the Women’s Care Center in Lexington, KY.


1. Centers for Disease Control and Prevention, “Sexually Transmitted Disease Surveillance, 2013.” Atlanta, GA: U.S. Department of Health and Human Services.2014. Accessed April 2015
2. Korenromp EL, Sudaryo MK, de Vlas SJ, et al. What proportion of episodes of
gonorrhoea and chlamydia becomes symptomatic? Int J STD AIDS. 2002; 13(2):91-101.
3. U.S. Preventive Services Task Force. Screening for chlamydial infection: recommendation statement. Ann Intern Med 2007; 147(2):128–134. Available from: Accessed April 30, 2015.
4. Meyers DS, Halvorson H, Luckhaupt S. Screening for chlamydial infection: an evidence update for the U.S. Preventive Services Task Force. Ann Intern Med 2007;147(2):135–142.
5. Centers for Disease Control and Prevention. Sexually transmitted diseases treatment guidelines, 2014. Accessed April 2015
6. Centers for Disease Control and Prevention. Chlamydia – CDC fact sheet. Available at Accessed February 27, 2013.
7. Bernstein KT, Marcus JL, Nieri G, Philip SS, Klausner JD. Rectal gonorrhea and chlamydia re-infection is associated with increased risk of HIV seroconversion. J Acquir Immune Defic Syndr 2010; 53:537–543.


Updated: May 2015