Chapter 46 Sexually Transmitted Infections: Chlamydia Trachomatis
INTRODUCTION
Description: The second most common sexually transmitted disease (STD) and most common bacterial STD is infection caused by Chlamydia trachomatis. More common than Neisseria gonorrhoeae by 3-fold, infections with C. trachomatis can be the source of significant complications and infertility.
Prevalence: Twenty percent of pregnant patients, 30% of sexually active adolescent women. Up to 40% of all sexually active women have antibodies suggesting prior infection. In 2005, 976,445 chlamydia infections were reported to the Centers for Disease Control and Prevention (CDC) from 50 states and the District of Columbia (496.5 cases per 100,000 females), up 5.1% from 2004.
Predominant Age: 15 to 30 years (85%), peak age 15 to 19 years. The Centers for Disease Control and Prevention recommend screening all sexually active women younger than age 26 years.
ETIOLOGY AND PATHOGENESIS
Causes: Infection by the obligate intracellular organism C. trachomatis. Chlamydia has a long incubation period (average, 10 days) and may persist in the cervix as a carrier state for many years.
Risk Factors: The risk of contracting chlamydial infection is five times greater with three or more sexual partners and four times higher for patients using no contraception or nonbarrier methods of birth control. Other factors are age younger than 26 years, new partner within the preceding 3 months, other sexually transmitted diseases, vaginal douching.
DIAGNOSTIC APPROACH
Workup and Evaluation
Laboratory: Cultures on cycloheximide-treated McCoy cells are specific and may be used to confirm the diagnosis, but these cultures are expensive, difficult to perform, and often not available. Two clinical screening tests are an enzyme-linked immunoassay (enzyme-linked immunosorbent assay) performed on cervical secretions and a monoclonal antibody test carried out on dried smears. When trying to obtain cervical cultures for chlamydia, plastic or metal-shafted rayon or cotton-tipped swabs are preferred. Wood-shafted or calcium alginate swabs reduce the yield of material when transport media are used because of leeching of toxic products into the media. Newer screening techniques using patientcollected vaginal swabs or urine specimens may be used but are not widely available.
Imaging: No imaging indicated. Ultrasonography may demonstrate free fluid in the cul-de-sac when pelvic inflammation is present.
