A 58-year-old man has problems urinating...a 65-year-old woman has abdominal pain...these may be common scenarios among older people, but many doctors aren't looking for an increasingly common culprit: sexually transmitted diseases. A 2012 study by British researchers revealed that syphilis, gonorrhea and chlamydia have increased in 45- to 65-year-olds in the UK, US and Canada, and 20 percent of adults accessing HIV treatment in Britain fall in that age group. Specifically, HIV diagnoses have doubled in people older than 50 between 2000 and 2009. And it shouldn't be surprising – more than 80 percent of senior citizens are sexually active, the study found. There are myriad reasons for the rise – one of which might be the ease of use of erectile dysfunction medications.