Lets all put this in perspective. How many people swim every year? In 9 year (2001-2010) there have been 32 known cases in the US. And only 121 cases since 1937-2007. This is not something I would worry about people!
There are soooo many other things that have a MUCH higher contraction rate than this!
Im still glad I don't swim in ponds and most lakes though! They gross me out anyways. I mainly swim in pools and thats it! LOL