Sexually transmitted diseases (STDs), once called venereal diseases, are among the most common infectious diseases in the United States today. More than 20 STDs have now been identified, and they affect more than 13 million men and women in this country each year. The annual comprehensive cost of STDs in the United States is estimated to be well in excess of $10 billion.

Understanding the basic facts about STDs – the ways in which they are spread, their common symptoms, and how they can be treated– is the first step toward prevention. The National Institute of Allergy and Infectious Diseases (NIAID), a part of the National Institutes of Health, has prepared a series of fact sheets about STDs to provide this important information. Research investigators supported by NIAID are looking for better methods of diagnosis and more effective treatments, as well as for vaccines and topical microbicides to prevent STDs.

It is important to understand at least five key points about all STDs in this country today:

1. STDs affect men and women of all backgrounds and economic levels. They are most prevalent among teenagers and young adults. Nearly two-thirds of all STDs occur in people younger than 25 years of age.
2. The incidence of STDs is rising, in part because in the last few decades, young people have become sexually active earlier yet are marrying later. In addition, divorce is more common. The net result is that sexually active people today are more likely to have multiple sex partners during their lives and are potentially at risk for developing STDs.

3. Most of the time, STDs cause no symptoms, particularly in women. When and if symptoms develop, they may be confused with those of other diseases not transmitted through sexual contact. Even when an STD causes no symptoms, however, a person who is infected may be able to pass the disease on to a sex partner. That is why many doctors recommend periodic testing or screening for people who have more than one sex partner.

4. Health problems caused by STDs tend to be more severe and more frequent for women than for men, in part because the frequency of asymptomatic infection means that many women do not seek care until serious problems have developed.
   
   :: Some STDs can spread into the uterus (womb) and fallopian tubes to cause pelvic inflammatory disease (PID), which in turn is a major cause of both infertility and ectopic (tubal) pregnancy. The latter can be fatal.
   
   :: STDs in women also may be associated with cervical cancer. One STD, human papillomavirus infection (HPV), causes genital warts and cervical and other genital cancers.
   
   :: STDs can be passed from a mother to her baby before, during, or immediately after birth; some of these infections of the newborn can be cured easily, but others may cause a baby to be permanently disabled or even die.
   
   
5. When diagnosed and treated early, many STDs can be treated effectively. Some infections have become resistant to the drugs used to treat them and now require newer types of antibiotics. Experts believe that having STDs other than AIDS increases one's risk for becoming infected with the AIDS virus.