What happened in America in 2013? (And in the past)

There's been some surprising (or not so surprising - depending on where you stand on the pessimism/optimism scale, I suppose) figures out regarding increasing rates of STDs in the US:

So, what happened in 2013?  Everyone suspects Grindr, but then I see it has been around since 2009, and The Guardian was giving it publicity in 2010.  If it was that app, it took a while to hit the STD rates.

The Atlantic had an article about syphilis's re-emergence last year, which also mentions Grindr, but it notes (as does the previous article) that there is no well researched basis for blaming it.   (How hard can it be to research this?   Why can't STD clinics ask that patients answer a short questionnaire on their use of such apps, or the internet, to find partners?) 

As for other reasons:  how about the loss of fear of HIV amongst Western men?   Surely it counts for something; but it astounds me that even if they are going to risk that, men will still take a punt on a disease that looks absolutely horrible, and  can hardly be hidden from friends and loved ones, at least it if gets to the secondary stage.  (You can Google images of the rash yourself.)

But having said that, there still seems something odd about 2013, and it seems no one knows what.

To get back to something resembling optimism again, how do current rates of STD's compare to those in past decades?   It would seem good figures are available for the US since the 1940's, and one thing that is surprising about them is the huge surge in one STD that, I assume, was a result of the 1960's sexual revolution:

As for syphilis, here's the more recent rate trend:

But go back further, and you realise just what a serious problem it was mid 20th century:

Now, that last graph is total cases, not cases per 100,000.  Here's what we really need for a graph comparison:

But, these graphs are confusing if they are including congenital syphilis, and you are only interested in the number of adults catching it. 

You can avoid that by looking at this table - where it is plain that primary and secondary syphilis had a peak 1940's rate in the USA of nearly 71 per 100,000. 

The rate today (not that I am making excuses for it!) is 7.5.  Pretty close to a tenth of the 1940's peak rate. 

Yeah, so while I can understand why the CDC is dismayed that it is on the way up after nearly disappearing, it's remarkable to realise the extent of problem it presented in the past...