Introduction
Sexually transmitted (venereal) diseases are infections that are passed from person to person through sexual contact.
Because sexual activity includes intimate contact, it provides an easy opportunity for organisms to spread from one person to another. A variety of infectious microorganisms can be spread by sexual contact. Bacterial sexually transmitted diseases (STDs) include syphilis, gonorrhea, nongonococcal urethritis and chlamydial cervicitis, lymphogranuloma venereum, chancroid, granuloma inguinale, and trichomoniasis. Viral STDs include genital warts, genital herpes (see Section 17, Chapter 198), molluscum contagiosum (see Section 18, Chapter 213), and HIV infection or AIDS (see Section 17, Chapter 199).
STDs are among the most common infectious diseases. It is estimated that over 3 million people contract gonorrhea and chlamydia every year in the United States--making these the two most common STDs in the country.
Although STDs usually result from having vaginal, oral, or anal sex with an infected partner, genital penetration is not necessary to spread an infection. Some diseases may also be transmitted by kissing or by close body contact. Also, the organisms responsible for some STDs (for example, HIV and hepatitis viruses) can be transmitted through nonsexual means, such as from mother to child at birth or through breastfeeding or exposure to contaminated food, water, blood, medical instruments, or needles.
Effective drugs are available for most STDs caused by bacteria, although a number of new antibiotic-resistant strains of bacteria have become widespread. Viral STDs, especially herpes and HIV, persist for life and have effective treatment but no known cure.
 See the figure Proper Condom Use.
Preventing or controlling STDs depends on practicing safe sex and getting prompt diagnosis and treatment. Knowing how to prevent the spread of STDs--in particular, knowing the proper method for using a condom--is crucial.
One strategy health care workers use to help control the spread of some STDs is contact tracing. Health care workers try to trace and treat (if treatment is available) all of an infected person's sexual contacts. People who have been treated are reexamined to make sure they are cured.
 See the sidebar Diseases That May Be Sexually Transmitted.
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