Are Legionella outbreaks on the rise or are we just looking more?

Yet another Legionella outbreak, this time in a retirement home in Ohio that has killed 6 people and sickened a couple dozen others.

I feel like the rate of new stories about Legionella outbreaks (at least in the US) has been rising a lot the last couple of years.   I found some data from the CDC that confirms an increase from 2000 to 2009 but I couldn’t find more recent hard data.  Wikipedia has a nice “List of Legionella Outbreaks” that supports my feeling, but I’m pretty sure the list is incomplete, particularly outside the US.  (Full disclosure:  I worked on Legionella while in Belgium for my first post-doc).    Here’s a graph I just made of the Wikipedia data:

The question about this that has bugged me for years is the question of incidence versus detection.   When I worked on Legionella in Europe from 2006-2010 it was a big deal there, large annual meetings, an international working group etc. etc.  But we rarely heard about it from the US.  I asked a number of people why they thought it was the case and they all gave some variant of “I’m sure they have Legionella all over the US… they’re just not looking for it”.  So when I moved back to the US and started working on the microbiology of the built environment I asked Norm Pace, who has done extensive microbial surveys of pools, showers, drinking water, etc. what he thought… and he said in all their work they really hadn’t come across much Legionella.   Hrm.

So what do people think?   Is Legionella slowly taking over the country or have we dramatically increased our surveillance of the bug?