Chlamydia is the most frequently reported bacterial sexually transmitted infection (STI), caused by the bacterium Chlamydia trachomatis. A sudden diagnosis can be alarming for individuals in committed relationships, often leading to the mistaken assumption of infidelity. While sexual contact is the primary route of transmission, the definition of “sexual contact” is broader than many people realize. Understanding the various ways the bacteria can spread and how long it can remain undetected is key to making sense of an unexpected positive test result.
Transmission Beyond Genital Intercourse
The bacteria that cause chlamydia are primarily spread through contact with infected genital fluids, such as semen or vaginal secretions. Penetration is not required for transmission to occur. Any intimate contact that allows these fluids to reach a susceptible mucous membrane—like those lining the mouth, throat, rectum, urethra, or cervix—can result in an infection.
Oral sex is a significant route of transmission, allowing the bacteria to infect the throat or the genital area of the partner receiving oral contact. Anal sex can transmit the infection to the rectum, which is a common site of infection that may have no noticeable symptoms. The use of shared sex toys that have not been properly cleaned between partners can also facilitate the spread of the bacteria.
Manual-to-genital contact, sometimes called “fingering,” also presents a transmission risk if infected fluids touch a partner’s genitals or other mucous membranes. Less commonly, if infected genital fluids come into contact with the eye, it can cause conjunctivitis, a form of pink eye. These forms of intimate contact can transmit the bacteria even when partners do not consider the activity to be traditional sex.
Non-Sexual Routes of Infection
The Chlamydia trachomatis bacterium is fragile and requires the warm, moist environment of human cells to survive, limiting its ability to spread outside of direct, intimate contact. Therefore, common myths about transmission are not supported by evidence. It is not possible to contract chlamydia from sharing toilet seats, swimming pools, hot tubs, or shared towels, as the bacteria cannot survive long enough on these surfaces.
The only medically recognized non-sexual route for chlamydia transmission involves mother-to-child passage during childbirth. A pregnant person with an active genital infection can transmit the bacteria to their baby as it passes through the birth canal. This vertical transmission can cause serious health issues for the newborn, most commonly leading to conjunctivitis (an eye infection) and sometimes pneumonia.
The Timeline of Asymptomatic Infection
The most common reason a person in a monogamous relationship receives a positive diagnosis is the prolonged, asymptomatic nature of the infection. Chlamydia is frequently referred to as a “silent infection” because a high percentage of infected individuals (up to 70% of women and 50% of men) experience no noticeable symptoms. This lack of symptoms means the infection can be carried unknowingly for a significant amount of time.
If left untreated, chlamydia can persist in the body for months or even years, and the person remains contagious. A positive test result indicates the presence of the bacteria today but does not reveal the date of acquisition. The infection could have been acquired from a previous partner long before the current relationship began, remaining dormant until detected through routine screening. Regular testing is the primary method for detecting chlamydia before it can cause long-term complications, such as pelvic inflammatory disease or infertility.