Other Names:
Chlamydid infections

Chlamydia is the common name for a type of sexually transmitted infection (STI).  It is caused by the bacterium called Chlamydia trachomatis that is spread by having sexual contact (vaginal, anal or oral sex) with an infected individual. This bacterial strain then resides in the cervix or vagina of a woman or in the urethra and rectum of both men and women. Chlamydia can be transmitted from one person to another via unprotected sexual contact or even by touching the genitals of someone who already has the disease.  Aside from sexual contact, other risk factors include age, being diagnosed with another STI in the past, having another infection and number of sexual partners.

Chlamydia is one of the most common sexually transmitted diseases, yet people tend to know less about it than syphilis and gonorrhoea. Women are more likely to suffer severe health consequences as a result of the infection. But many doctors who treat sexually active young women are not screening for the disease. Untreated, chlamydia may spread into the womb and fallopian tubes, leading to pelvic inflammatory disease (PID), ectopic pregnancy and infertility.  Preliminary evidence has linked chlamydia infection with increased cervical cancer risk. Infection with chlamydia may also increase the risk of being infected with HIV, the virus that causes AIDS. Chlamydia may also be transmitted during childbirth; a mother who has chlamydia may pass on the disease to her child when the baby passes through the vaginal canal. Eye damage and pneumonia are known side effects of chlamydia infection in newborns. Rectal or genital chlamydial infections may also continue for up to one year for an infant who has been infected by chlamydia at birth.  If left untreated in a man, sexually transmitted chlamydia can result in epididymitis (pain and inflammation in the epididymis) or the spread of the infection to the prostate gland, triggering fevers, painful intercourse and lower back pain.



Chlamydia pneumoniae causes bacterial pneumonia. The CDC estimates that there are 2 to 5 million cases of pneumonia and 500,000 pneumonia-related hospitalizations per year, but the overall incidence for pneumonia Chlamydia pneumoniae specifically is unknown.  Nevertheless, it’s an infection that’s quite common, as the CDC highlights that around 50 percent of adults have already been infected with this bacteria strain by the age of 20.  The illness is most common in school-age children, but it should be noted that all ages are at risk for infection. Chlamydia pneumoniae infection can be easily transferred from one person to another via coughing, sneezing or touching infected objects in areas such as military barracks, college dorms, care facilities or prisons.  Aside from pneumonia, people who are infected with the bacteria strain may also develop bronchitis, gradual cough or even pharyngitis, laryngitis and sinusitis. Older adults have more severe disease/s and recurring infections.

Chlamydia psittaci  is another chlamydia strain that can lead to a rare condition called psittacosis known as "parrot fever." The CDC reports that since 1996, less than 50 cases occur per year in the U.S., however, some instances may have been unreported or undiagnosed.  Humans usually get parrot fever from parrots (as the name implies) and other birds such as chickens, turkey, pigeons, and ducks when they handle the bird, breathe fine particles of the bird’s urine, feces, or other body excretions, touch their mouth to the bird’s beak, and/or get bitten by a bird. The usual signs of parrot fever are: Fever and chills; Nausea and vomiting; Muscle, joint, and chest pain; Weakness and fatigue; Diarrhoea; Dry cough; Shortness of breath; Intolerance to light

Symptoms and side effects of Chlamydia trachomatis are different for men and women. Men should watch out for these warning signs: Yellow, green, or white discharge from the penis; Burning feeling while urinating; Pain and swelling in one or both testicles (considered to be less common); Rectal pain, discharge and bleeding; Conjunctivitis in the eyes; Throat infection.  In men, chlamydia leads to epididymitis or inflammation and pain in the epididymis, the tube responsible for keeping the testicles in place. Chlamydia could also move to the prostate gland, resulting in fever, painful sexual intercourse and lower back discomfort.8 In rare cases, chlamydia can affect a man's ability to have children.

Women should check for these indicators that they are infected with chlamydia: Abnormal vaginal discharge that's either yellow or green; Burning feeling while urinating; Traces of blood in the urine; Increased urinary urgency and frequency (especially if the urethra is infected); Dyspareunia or pain during sexual intercourse; Discharge, bleeding and pain in the anus.


Western countries are experiencing a chlamydia epidemic. According to the UK Public Health Laboratory Service, the number of diagnosed infections soared by 76% between 1995 and 1999 with a 14% increase in infections in the single year between 1998 and 1999.  Infection rates in 1999 were highest in London, where they reached 155 per 100,000 men and 184 per 100,000 women. Doctors believe the number of known infections represent only about 10% of all cases.  Chlamydia remains the most common STI in the UK:  in a Health Protection Report by Public Health UK published June 2015, there were 206,774 diagnosed cases of chlamydia. These account for 47 percent of new STI cases in the country, the highest incidence rate when compared to genital warts, gonorrhea and genital herpes. Of these cases. 138,000 were among people aged 15 to 24 years old. Approximately 70% of women infected with chlamydia have no symptoms until more serious consequences arise. Over 50% of women with PID have had chlamydia, the sexually transmitted disease most likely to cause tubal damage. The 21-25-year age group is at the highest risk of contracting the disease. A 1993 UK report found only 7% of the 1,600 people surveyed had heard of chlamydia.

Statistics from the US Centers for Disease Control and Prevention (CDC) reported 1.6 million cases of chlamydia in 2016, up from 1.4 million reported cases of chlamydia. Young people aged 15 to 24 years old accounted for about two-thirds of these cases and it is said that 1 in 20 sexually active young women of the same age group already have chlamydia.  Infants born to women with untreated chlamydial cervical infection had chlamydial conjunctivitis or the redness and swelling in the clear membrane of the eyes (18 to 44 percent of infants) and chlamydial pneumonia (3 to 16 percent of infants).  If left untreated, 20% to 40% of women with chlamydia will go on to develop pelvic inflammatory disease, which can cause infertility and chronic pelvic pain. The infection often goes undetected, because most women with chlamydia have no symptoms. Two out of three primary care physicians surveyed did not screen sexually active teenage women for chlamydia.


Infection with Chlamydia pneumoniae has been implicated in people with difficult-to-treat breathing problems and asthma. This bacterium lingers in the lungs and can trigger inflammation and airway constriction.

Narrower Problems:
Chlamydid infections in animals
Related UN Sustainable Development Goals:
GOAL 3: Good Health and Well-being
Problem Type:
D: Detailed problems
Date of last update
30.08.2019 – 12:14 CEST