What Is Chlamydia?

Sexually transmitted diseases (STDs) are more common than many people might think—and not just among adults. In fact, according to the Centers for Disease Control and Prevention (CDC), nearly 20 million new STD infections occur each year. Almost half of them are among young people between the ages of fifteen and twenty-four.

Year after year, chlamydia, a common bacterial STD, remains the most frequently reported bacterial STD in the United States and Canada.
Year after year, chlamydia, a common bacterial STD, remains the most frequently reported bacterial STD in the United States and Canada. Overall, the number of reported cases in North America has increased steadily over the past twenty years. Some sources indicate that this reflects its prevalence throughout world history. As stated in The Microbial Biorealm, a report from Kenyon University’s biology department, chlamydia “has long plagued humanity as the most commonly contracted STD.” The CDC reported more than 1.5 million cases of chlamydia in 2015 (the most recent year for which data is available). Two-thirds of all reported chlamydia cases in 2015 were among persons under 25 years of age. Infection was highest in the age groups of 15–19 years and 20–24 years. However, since most people with the disease are not even aware of their infection—and therefore do not seek testing—this figure is much lower than the actual number of chlamydia cases. It is estimated that nearly three million Americans are infected annually. A disproportionate number of these are women. In 2012, women aged 20–24 years had the most chlamydia cases of any age group at 3,730.3 cases per 100,000 females. Young girls aged 15–19 had 2,994.4 reported cases per 100,000 females.

The Bacteria That Causes Chlamydia

Identified in 1907, chlamydia was once thought to be a virus (a kind of germ that cannot easily be treated with drugs). It was classified as a bacterium in the 1960s, when it was found to make its own proteins and have other characteristics of bacteria. The word “chlamydia” comes from the Greek root chlamys, a type of cloak that drapes over the shoulder. This refers to the way the chlamydia bacterium drapes itself around the nucleus of cells it attacks. It multiplies within the cell, then exits and moves on to other cells.

Chlamydia trachomatis
Chlamydia trachomatis bodies
CDC/Dr. E Arnum, Dr. N. Jacobs
Chlamydia trachomatis, the bacteria that causes the STD, is one of three species of the family of bacteria called Chlamydiaceae. Chlamydia trachomatis can also cause other infections, such as conjunctivitis (an eye infection) and pneumonia. Other species include Chlamydia pneumoniae (which can cause pneumonia, sinusitis, and bronchitis) and Chlamydia psittaci (which is carried by birds). But unless you are in medical school, “chlamydia” generally refers to the STD.

Who Gets Chlamydia?

Chlamydia and other STDs are not spread through casual contact. This means you can’t get chlamydia from a doorknob or toilet seat, or from shaking hands, hugging, or hanging out with someone who has it. It also is not spread through kissing. Chlamydia can affect anyone who has sexual contact with an infected person.

One reason young women are at such high risk for chlamydia is the fact that the cervix, the opening of the uterus (where a baby grows), of an adolescent girl is not fully developed. If the bacteria enter the body through her vagina, the underdeveloped cervix makes a better environment than a grown woman’s cervix for the bacteria to thrive. Young people may also be at higher risk because they are still developing their decision-making skills about sex and sexual activity.

How Is Chlamydia Spread?

Chlamydia bacteria live in an infected woman’s vaginal secretions or in an infected man’s semen (fluid that carries sperm). This means that if someone has chlamydia, he or she can pass it to someone else during vaginal, anal, or oral sex. The greater the number of sexual partners a person has, the greater the risk of contracting chlamydia. A pregnant woman can also pass chlamydia to her baby during birth, which can cause a number of health problems for the baby.

Female reproductive system
Female reproductive system
© Superstock, Inc.
Depending on how it was spread, the germ may invade the cervix, vagina, penis, rectum (the canal that connects the colon and anus), urethra (the tube that carries urine), or throat. In addition, it can travel from hand to eye, causing conjunctivitis (an eye infection also called pinkeye). In the United States, infection of the throat and eye is less common than infection of sexual organs. In impoverished regions, however, where crowding and unsanitary conditions are a problem, chlamydial eye infections are common. In parts of Africa and the Middle East, for example, chlamydia is often spread not only through sexual contact, but through infected people’s eye secretions. People with chlamydial eye infections can suffer from trachoma, a chronic inflammatory condition that can lead to blindness. It is estimated that worldwide, seven to nine million people are blind due to chlamydial infection.

What Are the Symptoms of Chlamydia?

Because of the way chlamydia operates, it is sometimes known as the “silent” disease. It is called this because it is able to cause infection without actually damaging cells. This is why more often than not, a person with chlamydia shows no symptoms. In some cases, symptoms never appear, even as the disease progresses and causes serious damage to a person’s reproductive system. The person may have no idea that he or she has the disease until a test proves it. This is especially true for women—fewer than 30 percent of those infected show symptoms.

If there are symptoms, they usually appear one to three weeks after sexual contact with an infected person. They may be mild and only last a short time. In women, symptoms include:

  • Increased or abnormal vaginal discharge

  • Pain or a burning feeling when urinating

  • Irritation or itching around the vagina

  • Bleeding after sexual intercourse or other abnormal vaginal bleeding

  • Pain in the lower abdomen or lower back, nausea, or fever, if the infection has spread to the uterus or fallopian tubes (where eggs move from the ovaries to the uterus)

Male reproductive system
Male reproductive system
LifeArt image © 2006 Lippincott Williams & Wilkins. All rights reserved
Among infected men, symptoms are slightly more common and may include:

  • A clear, white, or yellowish discharge from the penis

  • A burning feeling when urinating

  • Burning or itching around the opening of the penis

  • Pain or swelling of the testicles

If chlamydia is spread through anal sex, rectal symptoms may appear. For both men and women, these include pain, discharge, and bleeding. The appearance of one or more possible symptoms of chlamydia warrants a doctor’s visit.