Chlamydia – Causes, Signs and symptoms


Also called: Chlamydia Trachomatis Infection, Chlamydia Infection, Chlamydial Infection

Reviewed By:
David Slotnick, M.D.


Chlamydia is a common sexually transmitted disease (STD) caused by a bacterium called Chlamydia trachomatis. If left untreated, it can cause numerous medical problems, including serious damage to the reproductive organs.

Both women and men are affected, although there are far more reported cases of chlamydia in women than in men. It is transmitted through vaginal, anal and oral sex, but can also be passed from an infected mother to a newborn during vaginal childbirth. Younger women and those with multiple sexual partners are among those at a higher risk for chlamydia infection.

Most people with chlamydia do not usually have any symptoms. When they are present, signs and symptoms may include discharge from the vagina or penis, genital itching and lower abdominal pain. Because of the similarity in their symptoms, chlamydia is often mistaken for gonorrhea.

Chlamydia can be diagnosed through a urine test and by analyzing a fluid sample collected from the cervix or penis. The condition is easily treated with antibiotics. If left untreated, women with chlamydia may develop a serious infection of the uterus, fallopian tubes and other reproductive organs known as pelvic inflammatory disease (PID). In men, chlamydia can lead to a painful disease called epididymitis, which causes the testicles to swell. Both of these complications can lead to infertility.

Although abstinence is the best way to prevent infection, the risk of transmission may be reduced by practicing safe sex (e.g., using condoms, limiting the number of sexual partners). Those diagnosed with chlamydia should inform their current and past sexual partners immediately so they, too, can be tested for the STD. Treatment of partners reduces the risk of complications and of spreading the infection to other individuals. Because it is more common in younger women, the U.S. Centers for Disease Control and Prevention (CDC) recommends that women age 25 and under receive an annual screening test for chlamydia whether or not they exhibit symptoms.

About chlamydia

Chlamydia is a bacterial infection of the genital tract spread through sexual contact. If untreated, it can result in various medical complications, including damage to the reproductive organs.

The disease affects both women and men, although reported cases for women greatly exceed those for men. Chlamydia affects people in all age groups, but it is particularly prevalent among teenagers and young adults. According to the U.S. Centers for Disease Control and Prevention (CDC), the infection is most prevalent among women aged 20 to 25.

Chlamydia is sometimes confused with gonorrhea, another sexually transmitted disease (STD) caused by a different type of bacteria. Gonorrhea and chlamydia have similar symptoms and, if untreated, can have similar complications. Both are treated with antibiotics, but a different type of antibiotic is used to treat each disease.

In women, the bacteria that causes chlamydia often infects the cells of the cervix, but can spread to the uterus, fallopian tubes and ovaries. In men, the bacteria affect the urethra (the tube that carries urine from the bladder to outside the body), but can spread to the epididymis (the tube that carries the sperm from the testicles).

Chlamydia is transmitted through vaginal, oral or anal sex. Since chlamydia can be transmitted by anal sex, women or men who have anal intercourse can become infected in the rectum (the last several inches of the intestines that ends at the anus). Although it is less common, chlamydia can also infect the throats of women and men who have oral sex with an infected partner.

Chlamydia can also be passed from an infected mother to her infant during vaginal childbirth. Transmission to the newborn results from exposure to the mother’s infected cervix during birth. Infants with chlamydia may be born prematurely or have conjunctivitis (an infection of the eye, also known as “pink eye”) as well as pneumonia. Chlamydia is one of the most common STDs reported by physicians and other health providers to the CDC.

Estimates of the exact number of chlamydia cases vary. In 2004, there were 929,462 chlamydial infections reported to the CDC. However, since many people are not aware of their infections and are not tested, health officials estimate that the actual number of infections is much higher. Statistics vary among individual health organizations, but most estimates fall within the range of 2.8 million to 4 million chlamydia infections per year. 

Because chlamydia can lead to serious medical problems, there has been increased attention and screening for the disease in recent years. According to the CDC, from 1987 through 2003, the reported rate of chlamydial infection in women increased from 78.5 cases to 466.9 cases per 100,000 people. In 2004, there were three times more cases of chlamydia reported in women than in men. The jump in reported figures is likely the result of increased screening, use of more sensitive diagnostic tests and improved reporting, as well as the continued high incidence of the disease.

Risk factors and causes of chlamydia

Chlamydia is caused by the bacteria Chlamydia trachomatis, which is found in vaginal fluids and semen. Chlamydia trachomatis can be passed through vaginal, anal or oral sex.

There are a number of risk factors for chlamydia. They are:

  • Age. Because the cervix of teenage girls and young women is not fully matured and more susceptible to infection, this population faces a particularly high risk for infection if sexually active. Women and adolescents through age 20 years are at highest risk for the disease but data from the Centers for Disease Control and Prevention indicate the infection is most common among women from 20 to 25 years of age.

  • Number of sexual partners. The higher the number of sexual partners, the greater the risk of contracting chlamydia. The disease is more common in individuals who are not in long-term, monogamous relationships.

  • Lack of or improper condom use. People who do not use condoms, or who use them inconsistently or improperly during sexual intercourse are at a greater risk of becoming infected.

  • A sex partner with a sexually transmitted disease (STD). People with a sexual partner with an STD face a higher risk of getting chlamydia.

  • A sex partner who has not been treated. People with chlamydia whose sexual partners have not been treated face a higher risk of becoming reinfected. Also, people with a previous history of STDs are at a higher risk of developing chlamydia.

Signs and symptoms of chlamydia

Chlamydia is often called a “silent” disease because about 75 percent of women and 50 percent of men who are infected have no symptoms, according to the U.S. Centers for Disease Control and Prevention. If symptoms do occur, they usually appear within one to three weeks of exposure and may be mild.

Some signs and symptoms that may be present in people infected with chlamydia are:

  • Abnormal discharge from the penis or vagina
  • Burning sensation during urination
  • Lower abdominal or back pain
  • Nausea
  • Fever
  • Pain during intercourse
  • Burning or itching around the head of the penis
  • Swollen or tender testicles
  • Bleeding between menstrual cycles
  • Proctitis (inflammation of the rectum)

Patients diagnosed with chlamydia should inform their current and past sexual partners immediately. Testing and treatment of partners reduces the risk of complications and further spreading of the infection to other individuals.

Diagnosis methods for chlamydia

Chlamydia is diagnosed during a physical examination that includes a medical history and, in women, a pelvic examination. A physician may discuss sexual history, including number of sexual partners, past history of sexually transmitted diseases (STDs) and use of contraception.

Because chlamydia often produces no symptoms, the only conclusive way to diagnose the STD is with a laboratory test. Since the U.S. Centers for Disease Control and Prevention recommends that all sexually active women ages 25 and under receive a screening test, women may be given a test even if they have no symptoms. In addition, the U.S. Preventive Services Task Force (USPSTF) recommends that all pregnant women aged 25 years or younger be screened for the disease. However, some studies encouraged screening only in women with risk factors of the disease. Men may only be tested if they are symptomatic.

There are two types of tests that detect chlamydia:

  • Culture swab. For men, the physician may insert a slim swab into the end of the penis to get a sample from the urethra (the tube that carries urine from the bladder to outside the body). For women, the physician may take a sample of mucous from the cervix or vaginal discharge with a swab. In some cases, a sample may be taken from the anus. The sample is then sent to a laboratory where it is studied for the presence of bacteria.

  • Urine test. This may be performed on women and men. After collecting a sample of urine, it is sent to a laboratory where it is studied for the presence of the chlamydia bacteria.

Treatment and prevention of chlamydia

Chlamydia can be easily treated and cured with antibiotics, which may be administered in a single dose or taken over the course of a week. Pregnant women may be treated effectively with antibiotics without harming their fetus.

Patients should take all prescribed medication, even if symptoms are not present or disappear. Once chlamydia is diagnosed, all current and past sexual partners should be informed and treated to avoid reinfection. Patients and their sexual partners should avoid sexual contact until treatment is completed.

Patients are not usually retested for chlamydia after completing the medication unless symptoms persist or reinfection is suspected.

There are a number of steps that can be taken to reduce the risk of getting chlamydia. They include the following:

  • Practicing abstinence. The best way to prevent infection is to practice abstinence or avoid having vaginal, anal and oral sex.
  • Using condoms. Using a condom correctly during every sexual encounter can lower the risk of contracting chlamydia, as well as other sexually transmitted diseases (STDs).  For vaginal sex, use a male latex condom or a female polyurethane condom. For anal sex, use a male latex condom. For oral sex, use a dental dam, which is a rubbery material that can be placed over the penis or the vagina durning sexual contact.
  • Limiting sexual partners. Having multiple sexual partners increases the risk of getting chlamydia and other STDs. Maintaining a long-term, monogamous relationship is the best way to prevent contracting STDs. In addition, partners should honestly discuss their past sexual histories to understand the possible risks.

Because teenagers and young adults – especially females – are more susceptible to chlamydia infection, the U.S. Centers for Disease Control and Prevention recommends that sexually active women age 25 and under be given an annual screening test for chlamydia whether they exhibit symptoms or not. An annual screening test is also recommended for older women and men with risk factors for chlamydia, such as a new sexual partner or multiple sexual partners. Pregnant women, especially those aged 25 and younger, should be routinely screened for the disease as well to prevent transmission of the infection to the baby during birth.

Consequences of chlamydia

If left untreated, chlamydia can lead to serious reproductive and other health problems with both short- and long-term consequences. Like symptoms of the disease itself, symptoms of the damage chlamydia causes are often “silent.” Complications from untreated chlamydia include:

  • Pelvic inflammatory disease (PID). Chlamydia can spread into the uterus or fallopian tubes and cause PID (an infection of the uterus, fallopian tubes and other reproductive organs). This happens in up to 40 percent of women with untreated chlamydia. Although it may cause no signs or symptoms, PID can damage the fallopian tubes, ovaries and uterus, including the cervix. Untreated PID can lead to abscesses in the fallopian tubes and ovaries. The infection can cause scarring that may lead to infertility. PID affects up to 1 million women in the United States and half of all cases may be due to an untreated chlamydial infection.

  • Epididymitis. The epididymis is the tube that transports the sperm from the testicles. In rare cases, chlamydia bacteria can infect the epididymis and cause it to become inflamed and painful. This condition is called epididymitis and can lead to infertility.

  • Infertility. The inability to become pregnant after a year of continuous attempts. In women, a chlamydia infection can scar the fallopian tubes, preventing eggs from being fertilized. In men, chlamydia may infect the epididymis, leading to infertility.

  • An ectopic or tubal pregnancy. In this medical condition, a fertilized egg starts developing outside the uterus, usually in the fallopian tube but sometimes in the cervix, ovary or abdomen. The embryo must be removed to prevent rupture of internal organs.

  • Human immunodeficiency virus (HIV). Men and women infected with chlamydia are more likely to get HIV if exposed to the virus. The reason for the increased risk is that chlamydia causes a spike in the number of leukocytes (immune system cells) at the site of infection to help fight the infection. However, if exposed to HIV, it can infect these leukocytes.

  • Reiter’s syndrome. Rarely, genital chlamydial infection may cause Reiter’s syndrome. This involves arthritis (inflammation of the joints) that can be accompanied by skin lesions (abnormal tissue) and inflammation of the eye and urethra (the tube that carries urine from the bladder to the outside of the body).

In pregnant women, chlamydia infections may lead to premature delivery. Babies born to infected mothers can get conjunctivitis (an infection of the eye, also known as “pink eye”) as well as pneumonia.

Questions for your doctor regarding chlamydia

Preparing questions in advance can help patients to have more meaningful discussions regarding their conditions. Patients may wish to ask their doctor the following questions related to chlamydia:

  1. How do I know if I have chlamydia?
  2. How is chlamydia different from other sexually transmitted diseases?
  3. What type of treatment is best for my condition?
  4. What side effects will I experience with my treatment?
  5. What happens if I don’t get treated for chlamydia?
  6. How do I know which of my sexual partners are at risk for the disease?
  7. How will I know if my chlamydia has been successfully treated?
  8. If I get chlamydia once, do I have a greater chance of getting it again?
  9. Will chlamydia infection impact my chances of getting pregnant?
  10. If I am pregnant, will I receive a different treatment?
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