Prior to 1960, there were only two significant sexually transmitted diseases: syphilis and gonorrhea. Both were easily treatable with antibiotics. In the sixties and seventies this relatively stable situation began to change. For example, in 1976, chlamydia first appeared in increasing numbers in the United States. Chlamydia, particularly dangerous to women, is now the most common STD in the country. Then in 1981, human immunodeficiency virus (HIV), the virus which causes AIDS, was identified. By early 1993, between 1 and 2 million Americans were infected with AIDS, over 12 million were infected worldwide, and over 160,000 had died in the U.S. alone. Over 10% of the total U.S. population, 30 million people, are infected with herpes.