Human papillomavirus (HPV) is most common infection, followed by chlamydia, gonorrhea, syphilis, herpes, hepatitis B, HIV, and trichomoniasis.

According to the CDC, four of the STIs included in the analysis are easily treated and cured if diagnosed early: chlamydia, gonorrhea, syphilis, and trichomoniasis. But they say many such infections go undetected because they often have no symptoms.

Even without symptoms, these STIs can inflict serious health consequences. Undiagnosed and untreated chlamydia or gonorrhea, for example, can put a woman at increased risk of chronic pelvic pain and life-threatening ectopic pregnancy, and can also increase a woman's chance of infertility.

CDC estimates that HPV accounts for the majority of newly acquired STIs. While HPV is fairly common, it is also believed to be the leading cause of rare genital cancers including cervical cancer in women and penile and anal cancers in men.

According to the CDC and the Mayo Clinic, men who have sex with other men are at particular risk of developing these cancers. Wednesday's report recommended, "Screening at least once a year for syphilis, chlamydia, gonorrhea, and HIV for all sexually active gay men, bisexual men, and other men who have sex with men (MSM). MSM who have multiple or anonymous partners should be screened more frequently for STIs (e.g., at 3 to 6 month intervals)."

"In addition, MSM who have sex in conjunction with illicit drug use (particularly methamphetamine use) or whose sex partners participate in these activities should be screened more frequently," it added.

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The total number of new infections in the country has been growing over the last two decades, leading one CDC researcher to declare that the U.S. is facing an "ongoing, severe STI epidemic."

There were 15 million new infections reported in 1996 and 18.9 million reported in 2000.

According to CDC epidemiologist Catherine Lindsay, STIs have a large impact on the health and finances of men and women in the U.S., especially younger adults.

She told NBC News that that much of the $16 billion in annual health care costs that go to STI's is spent on patients with HIV/AIDS. Such patients require life-long care. While the U.S. study did not break down the number of HIV infections by population, a similar study in the UK showed that the deadly virus continues to be most common among homosexual men. The UK's Health Protection Agency estimates that one out of 20 men who have sex with men in that country now have HIV.

About a quarter of those infected are symptom-free and unaware they are contagious.

Because every STI is preventable, the CDC's Satterwhite argued, "we know that preventing STIs could save the nation billions of dollars each year."

UPDATED Feb. 16, 2013 to reflect ambiguity about the exact number of people who have an STI. The report initially stated that one in three Americans had an STI, based upon the total number of STIs - but that failed to take into account the possibility of multiple infections in the same person.