First, retirement communities and assisted living facilities are becoming like college campuses. They cram a lot of similarly aged people together, and when they do, things naturally happen. I mentioned these numbers to a friend, and she was not surprised. When her father moved into an assisted-living facility, she said, three women came by to introduce themselves within 30 minutes. And it wasn’t to compare Medicare pharmacy plans and premiums.

Second, older people are living longer and are in better health. As a result, they are remaining sexually active much later into life. Several major surveys, including the National Social Life, Health and Aging Project and the National Survey of Sexual Health and Behavior, report that among people age 60 and older, more than half of men and 40 percent of women are sexually active.

But while they are having a lot of sex, seniors didn’t seem to get the safe sex memo, or when it came through they ignored it because they did not think it applied to them. They obviously don’t have to worry about pregnancy. And they grew up before the safe sex era. So seniors might think they have no reason to use condoms. According to the 2010 National Survey of Sexual Health and Behavior, among college-age Americans, condoms are used in about 40 percent of sexual encounters, but only in about 6 percent of sexual encounters among those 61 and older. A study published in the Annals of Internal Medicine showed that older men who use Viagra and similar drugs are six times less likely to use condoms compared with men in their 20s.

Combine retirement communities, longer life, unfamiliarity with condoms and Viagra — and what do you get? You get an S.T.D. epidemic among the Social Security generation that rivals what we imagine is happening in those “Animal House” fraternities.