Chlamydia: Videos & Practice Problems

Chlamydia is a common sexually transmitted infection caused by Chlamydia trachomatis, a gram-negative bacterium that is spherical in shape but too small to be seen with a standard light microscope. Instead, infected epithelial cells reveal the presence of the bacteria within their cytoplasm. Unlike gonorrhea, which can replicate both inside and outside host cells, C. trachomatis is an obligate intracellular pathogen, meaning it can only reproduce within host cell vesicles.

Chlamydia often presents as non-gonococcal urethritis (NGU), characterized by urethral inflammation not caused by Neisseria gonorrhoeae. Diagnosis typically involves nucleic acid amplification tests (NAATs), such as PCR, performed on swabs from the vagina or urethra, or urine samples in males, since the bacteria are not visible under light microscopy.

This infection primarily targets the urethra in males and the cervix or uterus in females but can also infect the rectum, throat, and eyes. The bacterium has a unique biphasic life cycle involving two forms: the elementary body and the reticulate body. The elementary body is a small, metabolically inactive, infectious form that survives outside host cells, similar to a spore. Once inside a host cell, it transforms into the reticulate body, a larger, metabolically active form that replicates within the vesicle. After replication, reticulate bodies convert back into elementary bodies, which are released when the host cell lyses, spreading the infection.

Chlamydia can be transmitted from mother to newborn during childbirth, potentially causing conjunctivitis or pneumonia in infants. Routine prenatal screening and prophylactic antibiotic eye ointment for newborns help prevent these complications.

Many chlamydia infections are asymptomatic, especially in females, where approximately 75% of cases show no symptoms, and about 50% in males. When symptoms do occur, males may experience dysuria (painful urination), urethral discharge, itching, or swelling and pain in the testicles (orchitis) and epididymis (epididymitis). Females may notice vaginal discharge with odor, intermenstrual bleeding, itching, or pain during intercourse. Because symptoms overlap with gonorrhea, clinical presentation alone cannot distinguish between the two infections.

Untreated chlamydia can lead to serious complications such as pelvic inflammatory disease (PID), which involves chronic inflammation of the uterus and fallopian tubes, potentially causing painful menstruation, infertility, and increased risk of miscarriage.

Treatment for chlamydia is effective and typically involves antibiotics such as doxycycline or azithromycin. Unlike gonorrhea, chlamydia currently shows little to no antibiotic resistance. However, there is no lasting immunity after infection, so reinfection is possible. Consistent use of condoms significantly reduces the risk of transmission by providing a barrier to the bacteria at common sites of infection.

A 23-year-old sexually active man presenting with painful urination, occasional purulent urethral discharge, and soreness in the left epididymis suggests an infection consistent with epididymitis. These symptoms are commonly associated with two sexually transmitted infections (STIs): gonorrhea and chlamydia. Both infections can present with similar clinical features, making it difficult to distinguish between them based solely on symptoms.

To accurately diagnose these STIs, specific laboratory tests are essential. For gonorrhea, a microscopic examination of the urethral discharge can reveal characteristic Gram-negative diplococci, which are indicative of the infection. Additionally, nucleic acid amplification tests (NAATs), such as polymerase chain reaction (PCR), are highly sensitive and can detect gonorrheal DNA or RNA from urine samples or urethral swabs.

In contrast, chlamydia bacteria are not easily visualized under a standard microscope due to their intracellular nature. Therefore, diagnosis relies primarily on nucleic acid amplification tests (NAATs), which detect chlamydial genetic material from urine or urethral swabs. NAATs are considered the gold standard for diagnosing both gonorrhea and chlamydia because of their high sensitivity and specificity.

Treatment strategies differ between these two STIs due to varying patterns of antibiotic resistance. Gonorrhea has developed increasing resistance to many antibiotics, necessitating combination therapy to effectively eradicate the infection and prevent resistance spread. The recommended treatment involves a dual regimen of ceftriaxone, a third-generation cephalosporin, and azithromycin, a macrolide antibiotic. This combination targets the bacteria through different mechanisms, reducing the likelihood of resistance development.

On the other hand, chlamydia remains largely susceptible to standard antibiotics, allowing for monotherapy. Effective treatments include either doxycycline, a tetracycline antibiotic, or azithromycin. Both antibiotics inhibit bacterial protein synthesis but differ in dosing schedules and patient compliance considerations.

In summary, when evaluating a patient with urethritis and epididymitis symptoms, it is crucial to consider gonorrhea and chlamydia as potential causes. Confirmatory diagnosis relies on nucleic acid amplification tests, with microscopic examination aiding in gonorrhea detection. Treatment must be tailored accordingly: combination ceftriaxone and azithromycin for gonorrhea to combat antibiotic resistance, and doxycycline or azithromycin monotherapy for chlamydia. Understanding these diagnostic and therapeutic nuances ensures effective management of these common STIs.