Timing is everything in the disease business, which is probably why the United States Centers for Disease Control waited until Valentine's Day Eve to announce that the United States is home to 110 million sexually transmitted diseases. That amounts to 19.7 million new infections every year, half of which affect people 15 to 24. Unsurprisingly, the human papillomavirus is at the top of that list followed by chlamydia, gonorrhea, syphilis, herpes, hepatitis B, HIV, and trichomoniasis — though not necessarily in that order. And while we have ways of preventing these diseases, the problem appears to be getting worse. Studies from 1996 and 2000 estimated 15 million and 18.9 million cases, respectively, though different methods were used to collect the information in both cases.

Startled yet? The diseases collectively require nearly $16 billion worth of healthcare annually. The most expensive STD, unsurprisingly, is HIV/AIDS which requires lifetime care. Other ailments, like chlamydia, can lead to complications that can cost patients thousands of dollars out of pocket. In the words of CDC epidemiologist Catherine Lindsay, "STIs take a big health and economic toll on men and women in the United States, especially our youth." The CDC calls them STIs, rather than STDs. The lead author of one of two major studies released on Wednesday says the nation faces "an ongoing, severe, STI epidemic." All of these diseases, health professionals will point out, are preventable. Just don't have sex. Or do have sex and be vigilant about wearing condoms and getting tested. It's not romantic; it's real life.

Once again, Happy Valentine's Day.