Chlamydia is a bacterial sexually transmitted infection (STI) caused by the organism Chlamydia trachomatis. It is one of the most common bacterial STIs globally, yet it frequently goes undiagnosed because it often produces no symptoms at all. This asymptomatic nature, often leading to the term “silent infection,” is the primary reason it spreads widely and can lead to severe, long-term health complications if left untreated. Public health efforts focus heavily on routine screening rather than waiting for symptoms to appear due to this high percentage of silent cases.
Prevalence of Asymptomatic Cases
The proportion of Chlamydia trachomatis infections that are asymptomatic is notably high, but it varies depending on the infected person’s sex and the specific site of infection. For women, the percentage of infections without noticeable symptoms is consistently reported to be between 70% and 80%. Up to four out of every five women who contract chlamydia may not experience signs that prompt them to seek medical care.
Among men, the rate of asymptomatic infection is slightly lower but still represents a majority of cases, typically around 50% or more. Some studies report the absence of symptoms in men to be as high as 73.9% to 94.6% in urogenital infections, suggesting significant variability across populations. Since many infected individuals have no symptoms, they can unknowingly transmit the bacterium, perpetuating the spread of the infection.
The location of the infection also influences the likelihood of symptoms. While chlamydia primarily affects the genital tract, it can also infect the rectum and pharynx through anal and oral sexual contact. Rectal and pharyngeal infections are often asymptomatic, even when the genital infection is not. This silent nature at multiple infection sites makes comprehensive screening, including extragenital testing when indicated by sexual history, a necessary strategy for effective detection and control.
Risks of Silent Infection
An asymptomatic infection is dangerous precisely because it progresses without presenting any warning signs, allowing the bacteria to cause chronic inflammation and damage over time. The most serious consequence for women is Pelvic Inflammatory Disease (PID), which occurs when the infection ascends to the upper reproductive tract. PID can cause scarring in the fallopian tubes, which may lead to chronic pelvic pain, ectopic pregnancy, or tubal factor infertility.
For men, an untreated infection can lead to urethritis, an inflammation of the urethra, even if subclinical. A more specific complication is epididymitis, which is the inflammation of the tube that carries sperm from the testicles. While less common than PID in women, epididymitis can cause pain and swelling in the testicles and may, in rare cases, affect fertility.
Beyond the direct damage to the reproductive system, an untreated chlamydia infection can also increase the risk of contracting and transmitting Human Immunodeficiency Virus (HIV). If a pregnant individual is infected, the bacterium can be passed to the newborn during delivery, potentially causing conjunctivitis or pneumonia in the infant.
Current Screening Recommendations
Since the majority of chlamydia cases are asymptomatic, relying on symptoms for diagnosis is an insufficient public health approach. To counter this, health organizations like the Centers for Disease Control and Prevention (CDC) recommend proactive, routine screening for specific populations. The primary target for annual screening is all sexually active women younger than 25 years of age.
Screening is also recommended for women aged 25 years and older who have increased risk factors, such as having a new sexual partner, multiple partners, or a partner diagnosed with an STI. Pregnant individuals who are younger than 25 or at increased risk should be screened at their first prenatal visit, with rescreening during the third trimester for those who remain at risk. This targeted approach aims to catch silent infections in population groups with the highest prevalence and risk for complications.
For men, routine, widespread screening is not universally recommended, but it is strongly considered in clinical settings with a high prevalence of chlamydia, such as adolescent clinics or STI specialty clinics. Men who have sex with men (MSM) are a key target group and are advised to be screened at least annually at all sites of contact, including the urethra and rectum. The rationale for these guidelines is to interrupt the silent transmission chain and prevent the severe, avoidable complications caused by the bacterial infection.