Hmmmm.
Just an FYI on something I noticed that you might be interested in. The Sawyer filters aren't suitably effective against viruses according to
http://chppm-www.apgea.army.mil All the info I could find on that site regarding Sawyer filters were not for the SP135, but rather the SP130 and SP120 which are only good to 1 micron. I think the SP135 is relatively new, because I can only order it online and from very few places whereas I can buy the Sawyer SP130 at Wal-Mart, Dick's Sporting Goods and so on locally.
I could've missed the report regarding the SP135 though.