According to the CDC, the outbreak in the US began between November 15 and December 8, 2017 and there have been documented cases so far in the following states: New York, California, Connecticut, Illinois, Indiana, Michigan, Nebraska, New Hampshire, Ohio, Pennsylvania, Virginia, Vermont, and Washington. In its investigation, both the CDC and FDA say that the type of E. coli that's making people sick is similar to the one involved in the Canadian outbreak, but have stopped short of putting out a warning, citing a lack of evidence. Still, if you have a compromised immune system, or just don't want to risk even the slightest chance of developing nasty E. coli symptoms, it couldn't hurt to steer clear.
Now may be the the perfect time to branch out of your salad comfort zone. After all, caesar salads aren't all that healthy anyway.