10 Essential Facts About Chlamydia

If you’re sexually active, you should know about chlamydia, a common sexually transmitted bacterial infection. These 10 facts about chlamydia will bring you up to speed on who’s at risk, why regular screening is so important, and how to avoid getting it and other sexually transmitted infections (STIs).

1. Chlamydia Is Common, but Many People Don’t Realize They Have It

About 4 million chlamydia infections were reported to the Centers for Disease Control and Prevention (CDC) in 2018, but the real number is likely higher because chlamydia is considered an underreported infection.

“The number of reported cases is substantially lower than the true estimated incidence,” says Bradley Stoner, MD, PhD, associate professor emeritus at the Washington University School of Medicine in St. Louis and former president of the American Sexually Transmitted Diseases Association.

The National Notifiable Diseases Surveillance System relies on state and local public health departments to collect and report data on chlamydia (and certain other STIs) to the CDC. Those public health departments depend on individual physicians, hospitals, and laboratories to report cases of chlamydia to them. Accurate statistics require all parties to routinely comply with disease-reporting mandates.

2. Chlamydia Is Caused by Sexually Transmitted Bacteria 

The bacteria Chlamydia trachomatis causes chlamydia infection, which usually occurs in the genital tract, so the cervix in women and the penis in men. In both women and men, the bacteria may also infect the rectum and the throat.

“Infections are spread during any kind of sexual activity: vaginal, anal, or oral intercourse,” says Jonathan Schaffir, MD, clinical professor of obstetrics and gynecology at Ohio State University Wexner Medical Center in Columbus.

Chlamydia trachomatis can also cause conjunctivitis (pink eye) if the bacteria come into contact with the eyelids or the clear membrane covering the white of the eye.

Because chlamydia infections often cause no symptoms, individuals who have one may not seek medical attention or get treated for it. However, anyone who is infected with chlamydia can pass it to other people, who can, in turn, pass it to others.

3. Young Sexually Active Women Are Most Susceptible

Women between ages 15 and 24 are most likely to be newly infected with chlamydia, according to the CDC, but anyone who is sexually active — male or female — can be infected. Men who have oral or anal sex with men are also at risk, notes the CDC. The CDC recommends regular chlamydia screenings for people at an increased risk of contracting it.

You should be screened annually for chlamydia if you are:

• A sexually active woman under age 25
• A woman age 25 or older who has multiple sexual partners
• A woman whose sexual partner may have multiple sexual partners
• Pregnant and under age 25 or pregnant and age 25 or older with an increased risk (pregnant women at risk for chlamydia should be screened as early as possible in the pregnancy, with a repeat screening in the third trimester)
• A man who has sex with men
• At an increased risk for other health reasons

“I would emphasize that young women should be screened if they engage in any sexual behavior that puts them at risk because [chlamydia] often has no symptoms, and early treatment is important to avoid long-term damage and infertility,” Dr. Schaffir says.

Screening for chlamydia is painless: It usually involves testing a urine sample or a specimen swabbed from the vagina or penis. Some lab tests for chlamydia can use specimens from the throat or rectum.

4. Chlamydia Is Only Contagious From Person to Person

You can only get chlamydia by having intimate sexual contact with an infected person, not from casual contact, touching another person’s clothing, or consuming contaminated food or water.

“The chlamydia organism lives only in human cells and cannot be transmitted by external contact, such as towels or toilet seats,” Schaffir says.

5. Symptoms Can Differ for Men and Women

“By and large, most cases of chlamydia are asymptomatic — they are picked up by screening, which is why it’s so important to have good screening programs in place,” notes Dr. Stoner. Men or women who have chlamydia symptoms may experience painful urination.

Women may also have these symptoms:

• Abdominal pain
• Smelly discharge from the cervix
• Pain during sex
• Bleeding after sex
• Bleeding between periods

And men may have these symptoms:

• Discharge from the penis
• Painful testicles

6. Chlamydia Infection May Have Long-Term Health Consequences

For women, the long-term effects of an untreated chlamydia infection may include:

• Severe infection with pain and fever requiring a hospital stay
• Pelvic inflammatory disease, an infection of the upper reproductive tract
• Scarring in the reproductive tract that causes infertility
• Higher risk of ectopic pregnancy

Men are less likely than women to have major health problems linked to chlamydia, although they can develop epididymitis, an inflammation of a structure within the testicles called the epididymis that can result in infertility.

A chlamydia infection can sometimes result in reactive arthritis in both men and women.

7. A Woman Can Pass Chlamydia on to Her Newborn During Childbirth 

When a baby is exposed to the mother’s untreated chlamydia infection during childbirth, the infant can contract an eye infection or pneumonia, requiring treatment with antibiotics. Chlamydia during pregnancy also raises the risk of premature birth and low birth weight.

8. Antibiotics Are a Highly Effective Cure for Chlamydia Infection

Antibiotics prescribed for chlamydia include:

• azithromycin (Zithromax)
• doxycycline (Doryx)

A single oral dose of Zithromax is the most common treatment. Other drugs may be given in varying doses for a period of up to a week. Most cases of chlamydia clear up within a week after you start on antibiotics.

“If you think you have been exposed to chlamydia,” Stoner says, “see your healthcare provider to receive antibiotic medication to prevent the onset of infection.”

The partners of individuals diagnosed with chlamydia will need treatment, too, and in some states they can get it without a doctor visit through a practice called “expedited partner therapy,” in which the first person treated delivers the treatment to their partner or partners.

9. You Can Get Chlamydia More Than Once

With some diseases, having one infection makes you immune to future infections. That’s not the case with chlamydia. If you engage in sexual activity with a person who has a chlamydia infection, you can get it again, even if you’ve just completed treatment for it.

“Both partners should be treated before reinitiating sexual intercourse to prevent relapse,” Schaffir says.

10. Chlamydia Can Be Prevented

The most effective way to avoid getting a sexually transmitted infection is to not have sex. However, if you wish to have sexual contact, you can reduce your risk of infection with these actions:

• Minimizing the number of partners with whom you have intimate contact
• Asking your partners to get screened for STDs (and getting screened yourself) before engaging in sexual activity
• Always using latex condoms when having intercourse of any kind

Additional reporting by Ingrid Strauch.