Chlamydial Infections

Chlamydial (kla-MID-ee-al) infections are caused by three species of microorganism * . Chlamydia trachomatis can cause eye or lung infections and can also infect the urinary and genital areas of both men and women. Chlamydia pneumoniae causes infections of the respiratory tract, and Chlamydia psittaci causes ornithosis, known as parrot fever, which is similar to the flu.

What Diseases Are Caused by Chlamydial Infections?

Chlamydia trachomatis

In the United States, Chlamydia trachomatis (tra-KO-ma-tis) is responsible for more cases of sexually transmitted infections (STIs) than any other organism. Sexually transmitted infections are passed from one partner to another during sexual activity. According to the Centers for Disease Control and Prevention (CDC), in 2013 more than 1.4 million cases were reported in the United States, but an estimated 2.86 million infections by Chlamydia trachomatis occur annually, including those not reported to the CDC.

Chlamydia trachomatis also causes an eye infection called trachoma (tra-KO-ma). This inflammation of the membrane covering the eye causes the eye to become irritated and red with a thick discharge. Infants whose mothers have chlamydial infections may become infected during birth. These infants can develop eye infections a few days after birth or pneumonia several weeks after birth.

Chlamydia pneumoniae

Chlamydia pneumoniae (noo-MO-neeeye) can cause infections in the respiratory tract. The result can be bronchitis * , pneumonia * , or pharyngitis * . In the United States, Chlamydia pneumoniae is one of the leading causes of pneumonia in people between the ages of 5 and 35 years.

Chlamydia psittacosis

The illness psittacosis (sit-a-KO-sis), also called ornithosis or parrot fever, is caused by Chlamydia psittaci carried by birds (mainly parrots, parakeets, and lovebirds). In human beings, it causes an illness that is like the flu. Only people who work closely with birds, such as pet-store employees or trainers of carrier pigeons, are liable to contract this disease.

How Are Chlamydial Infections Transmitted?

Chlamydial infections are passed from one person to another through direct contact. Sexually transmitted chlamydia is passed from one person to another by direct sexual contact, and the people at most risk are those who have unprotected sex (sexual intercourse without use of a condom) or multiple sex partners.

Parrot fever is caused by inhalation of dust from feathers and droppings or by the bite of an infected bird. Trachoma is transmitted by eye-to-eye or hand-to-eye contact, eye-seeking flies, or by sharing contaminated articles such as towels, handkerchiefs, or eye makeup.

Who Are at Risk for Chlamydial Infections?

Those at greatest risk for Chlamydia trachomatis infections include sexually active individuals, especially those with partners who have the infection. Unborn babies of mothers with the disease are also at risk for infection during birth. People who work with birds that are illegally brought into the United States are at risk of infection with Chlamydia psittaci.

What Are the Symptoms of Chlamydial Infections?

The most common symptom of Chlamydia trachomatis infections in men and women is a burning sensation during urination. Unfortunately, many women who are infected do not have any symptoms. If they are pregnant and do not know that they have been infected, they may unknowingly pass the disease to their baby during birth. Besides a burning sensation when urinating, a person with Chlamydia trachomatis may have an abnormal discharge from the genital area. The genital area may become inflamed, and in women, the inflammation can spread to the internal reproductive organs. Women may then develop pelvic inflammatory disease (PID), a condition that causes a woman to become infertile (unable to become pregnant).

Transmission Electron Micrograph (TEM) of chlamydia bacteria.

Transmission Electron Micrograph (TEM) of chlamydia bacteria.
David M. Phillips/Science Source.
* occurs, and vision is diminished or completely lost.

Parrot fever has an incubation * period of one to three weeks. There is then a sudden onset of fever, chills, loss of appetite, and fatigue. Later a cough develops, which progresses to pneumonia. Up to 30 percent of people who have untreated parrot fever die.

How Are Chlamydial Infections Treated?

Chlamydial infections can be successfully treated with antibiotics * . Because untreated chlamydial infections can lead to serious and permanent problems, possible infections should be treated and evaluated by a doctor as soon as possible. While being treated for genital infections due to chlamydia, individuals should inform their sexual partners, who should be tested and treated if necessary. Parents of newborn children should be alert to the condition of the baby's eyes. If they become red, swollen, or have a thick discharge, a physician should be contacted immediately. Persistent coughing by a newborn is also a signal to call a doctor.

Can Chlamydial Infections Be Prevented?

The best prevention for genital infection by chlamydia is to avoid sexual contact with an infected person. Abstaining from sexual relations is the only certain way to avoid contracting Chlamydia trachomatis because it is common for infected people not to know they have the infection.

Blindness due to trachoma infection can be prevented by giving a single dose of the antibiotic azithromycin to individuals who live in areas where the condition is endemic * .

Parrot fever can be prevented by buying birds from reputable pet stores or breeders who sell imported birds that have been quarantined * , examined, and fed antibiotic-treated bird feed for 45 days.

See also Pelvic Inflammatory Disease (PID) • Sexually Transmitted Infections (STIs): Overview • Zoonoses: Overview


Books and Articles

Kamberg, Mary-Lane. Chlamydia (Your Sexual Health). New York: Rosen Young Adult, 2015.


National Women's Health Resource Center. “Chlamydia.” . (accessed November 28, 2015).


American Sexual Health Association. PI Box 13827, Research Triangle Park, NC 27709. Telephone: 919-361-8400. Website: (accessed March 28, 2016).

Centers for Disease Control and Prevention. 1600 Clifton Rd., Atlanta, GA 30333. Toll-free: 800-311-3435. Website: (accessed March 28, 2016).

National Women's Health Resource Center. 157 Broad St., Suite 200, Red Bank, NJ 07701. Toll-free: 877-986-9472. Website: (accessed March 28, 2016).

* microorganism is a tiny organism that can be seen only by using a microscope. Types of microorganisms include fungi, bacteria, and viruses.

* bronchitis (brong-KYE-tis) is a disease that involves inflammation of the larger airways in the respiratory tract, which can result from infection or other causes.

* pneumonia (nu-MO-nyah) is inflammation of the lungs.

* pharyngitis (far-in-JI-tis) is inflammation of the pharynx, part of the throat.

* cornea (KOR-nee-uh) is the transparent circular layer of cells over the central colored part of the eyeball (the iris) through which light enters the eye.

* incubation (ing-kyoo-BAY-shun) is the period of time between infection by a germ and when symptoms first appear. Depending on the germ, this period can be from hours to months.

* antibiotics (an-tie-by-AH-tiks) are drugs that kill or slow the growth of bacteria.

* endemic (en-DEH-mik) describes a disease or condition that is present in a population or geographic area at all times.

* quarantine is the enforced isolation (for a fixed period) of apparently well people or animals who may have been exposed to infectious disease.

Disclaimer:   This information is not a tool for self-diagnosis or a substitute for professional care.

(MLA 8th Edition)