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Introduction to Sexually Transmitted Diseases


Useful Background for the Study of STDs


Overview of the Etiologic Agent

With over 3 to 4 million people infected each year, chlamydia is the most common bacterial sexually transmitted disease (STD). Chlamydial infections affect a wider spectrum of people than do gonococcal infections. However, adolescents, heterosexuals (particularly those with new or multiple partners), and African Americans have higher rates of chlamydial infections than the rest of the population. Rates are higher in women than men, but this is because women are screened for the infection much more often than men.

Chlamydia is cased by the organism Chlamydia trachomatis. It is a member of the Chlamydiaceae family, and is an intracellular bacterium that was previously thought to be a virus. C. trachomatis are obligate parasites of eukaryotic cells that contain DNA and RNA. They live in columnar mucosal cells, and thus one needs cellular material to culture the organism. Different serotypes of C. trachomatis cause different types of illnesses are transmitted in different types of ways. Here, serotypes D through K, as well as L1 though L3 are discussed, since these are the serotypes transmitted through sexual relations.


C. trachomatis serotypes D through K, the most common in the United States, are efficiently transmitted through vaginal or anal intercourse. Orogenital transmission is rare. The incubation period for the bacterium is 1 to 5 weeks, with 1 to 3 weeks being the most common incubation period. Transmission rates are equal between males and females.

Signs, Symptoms and Treatment of Serotypes D through K

One of the most important things to remember with chlamydia is that up to 80 percent of women and 25 percent of men are asymptomatic of their infection.

Men infected with C. trachomatis experience painful urination, penile discharge and urethral itching. Because the symptoms are much like those with gonococcal infection, men with chlamydia and urethritis may be diagnosed with "non-gonococcal urethritis." If chlamydia goes untreated in a man, it can lead to epididymitis and prostatitis.

As stated earlier, most women infected with C. trachomatis are unaware of their infection. The most common site of infection is the cervix, which may appear with discharge or inflammation. The urinary tract may also be infected, and so a woman may complain of painful or frequent urination. Complications of chlamydial infection in women include PID (which can lead to infertility and increased risk of ectopic pregnancy) and perihepatitis. Mothers can also pass on chlamydia to their newborns. Most newborns with chlamydial infections will experience conjunctivitis, and a smaller number will develop pneumonia.

Signs, Symptoms and Treatment of Serotypes L1 through L3

C. trachomatis serotypes L1 through L3 are very rare in the United States and occur mainly in Asia, Africa and South America, but they are passed sexually and cause an infection called lymphogranuloma venereum (LGV). Only about a hundred cases are seen in the United States each year. LGV causes a systemic infection that begins with a lesion on the penis, labia or in the vagina. Some people do not get a lesion but instead get urethritis or cervicitis. Two to 6 weeks later the infected person experiences a swelling of their inguinal lymph nodes, which typically drain. Complications include progressive ulceration and fistulas in the genital and rectal tissues.

Treatment of chlamydia and lymphogranuloma venereum is with antibiotics. A person who receives treatment should return to his or her health care provider for a test to make sure the infection has been eradicated.

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