Estimating how many sexually transmitted disease or infection cases occur is not a simple or straightforward task. First, most STDs/STIs can be "silent," causing no noticeable symptoms. These asymptomatic infections can be diagnosed only through testing. Unfortunately, routine screening programs are not widespread, and social stigma and lack of public awareness concerning STDs/STIs often inhibits frank discussion between health care providers and patients about STD/STI risk and the need for testing.
-- ASHA. Sexually Transmitted Diseases in America: How Many Cases and at What Cost? December 1998.
More than half of all people will have an STD/STI at some point in their lifetime. 
Recent estimates from the Centers for Disease Control and Infection show that there are 19.7 million new STIs every year in the U.S. 
In 2008, there were an estimated 110 million prevalent STIs among women and men in the U.S.. Of these, more than 20% (22.1 million) were among women and men aged 15 to 24 years. 
The total estimated direct cost of STIs annually in the U.S. is $15.6 billion (2010 US dollars). 
In a national survey of US physicians, fewer than one-third routinely screened patients for STDs/STIs. 
Less than half of adults ages 18 to 44 have ever been tested for an STD/STI other than HIV/AIDS.
Each year, one in four teens contracts an STD/STI. 
One in two sexually active persons will contact an STD/STI by age 25. 
About half of all new STDs/STIs in 2000 occurred among youth ages 15 to 24.  The total estimated costs of these nine million new cases of these STDs/STIs was $6.5 billion, with HIV and human papillomavirus (HPV) accounting for 90% of the total burden. 
Of the STDs/STIs that are diagnosed, only some (gonorrhea, syphilis, chlamydia, hepatitis A and B) are required to be reported to state health departments and the CDC.
One out of 20 people in the United States will get infected with hepatitis B (HBV) some time during their lives.  Hepatitis B is 100 times more infectious than HIV. 
Approximately half of HBV infections are transmitted sexually.  HBV is linked to chronic liver disease, including cirrhosis and liver cancer.
Hepatitis A, hepatitis B and HPV are the only vaccine-preventable STDs/STIs. (Not all HPV types are covered by the vaccine, so women who receive it still need Pap tests.)
It is estimated that as many as one in five Americans have genital herpes, a lifelong (but manageable) infection, yet up to 90 percent of those with herpes are unaware they have it. 
With more than 50 million adults in the US with genital herpes and up to 776,000 new infections each year, some estimates suggest that by 2025 up to 40% of all men and half of all women could be infected. [13,14,15]
Over 14 million people acquire HPV each year ,and by age 50, at least 80 percent of women will have acquired genital HPV infection.  Most people with HPV do not develop symptoms.
Each year, there are almost 3 million new cases of chlamydia, many of which are in adolescents and young adults.  The CDC recommends that sexually active females 25 and under should be screened at least once a year for chlamydia, even if no symptoms are present.
About two-thirds of young females believe doctors routinely screen teens for chlamydia.  However, in 2003 only 30% of women 25 and under with commercial health care plans and 45% in Medicaid plans were screened for chlamydia. 
At least 15 percent of all American women who are infertile can attribute it to tubal damage caused by pelvic inflammatory disease (PID), the result of an untreated STD. Consistent condom use reduces the risk of recurrent PID and related complications: significantly, women who reported regular use of condoms in one study were 60 percent less likely to become infertile. 
Consistent condom use provides substantial protection against the acquisition of many STDs, including statistically significant reduction of risk against HIV, chlamydia, gonorrhea, herpes, and syphilis. [20,21,22]
Some studies show that, for those who already have a clinically apparent genital HPV infection, using condoms promotes the regression of HPV lesions in both women and men. [23,24]
Koutsky L. (1997). Epidemiology of genital human papillomavirus infection. American Journal of Medicine, 102(5A), 3-8.
Satterwhite CL, et al. Sexually transmitted infections among U.S. women and men: Prevalence and incidence estimates, 2008. Sex Transm Dis 2013; 40(3): pp. 187-193
Owusu-Edusei K, et al. The estimated direct medical cost of selected sexually transmitted infections in the United States, 2008. Sex Transm Dis 2013; 40(3): pp. 197-201.
St Lawrence JS et al. (2002). STD screening, testing, case reporting, and clinical and partner notification practices: a national survey of US physicians. American Journal of Public Health, 92, 1784-1788.
Alan Guttmacher Institute. (1994). Sex and America's Teenagers. New York: Alan Guttmacher Institute.
Cates JR, Herndon NL, Schulz S L, Darroch JE. (2004). Our voices, our lives, our futures: Youth and sexually transmitted diseases. Chapel Hill, NC: University of North Carolina at Chapel Hill School of Journalism and Mass Communication.
Weinstock H, Berman S, Cates W, Jr. (2004). Sexually transmitted diseases among American youth: Incidence and prevalence estimates, 2000. Perspectives on Sexual and Reproductive Health, 36, 6-10.
Chesson HW, Blandford JM, Gift TL, Tao G, Irwin KL. (2004). The estimated direct medical cost of sexually transmitted diseases among American youth, 2000. Perspectives on Sexual and Reproductive Health, 36, 11-19.
American Social Health Association. (2005). State of the Nation 2005: Challenges facing STD prevention in youth. Research Triangle Park, NC: American Social Health Association.
National Committee for Quality Assurance. (2004). The state of health care quality: 2004. Washington, DC: NCQA.
Ness RB et al. (2004). Condom use and the risk of recurrent pelvic inflammatory disease, chronic pelvic pain, or infertility following an episode of pelvic inflammatory disease. American Journal of Public Health, 2004, 94:1327-1329.
Crosby RA et al. (2003). The value of consistent condom use: a study of sexually transmitted disease prevention among African American adolescent females. American Journal of Public Health, 93, 901-902.
Holmes KK, Levine R, Weaver M. (2004). Effectiveness of condoms in preventing sexually transmitted infections. Bulletin of the World Health Organization, 82, 454-464.
Shlay JC et al. (2004). Comparison of sexually transmitted disease prevalence by reported level of condom use among patients attending an urban sexually transmitted disease clinic. Sexually Transmitted Diseases, 31, 154-160.
Bleeker MC et al. (2003). Condom use promotes regression of human papillomavirus-associated penile lesions in male sexual partners of women with cervical intraepithelial neoplasia. International Journal of Cancer, 104, 804-810.
Hogewoning CJ et al. (2003). Condom use promotes regression of cervical intraepithelial neoplasia and clearance of human papillomavirus: A randomized clinical trial. International Journal of Cancer, 107, 811-816.
Myers ER, McCrory DC, Nanda K, Bastian L, Matchar DB. Mathematical model for the natural history of human papillomavirus infection and cervical carcinogenesis. Am J Epidemiol. 2000;151:1158-1170.