In April 2011, 14 people in Canada were stricken with E. coli O157:H7, including one death, linked to walnuts from California.

Many questions were raised about the link, and there was never any follow-up report (not one that I saw).

Today, the Canadian Food Inspection Agency (CFIA) and Compass Food Sales warned the public not to consume Compass brand in-shell California Walnuts described below because the product may be contaminated with Salmonella.
The following walnuts, product of USA, are affected by this alert:

This product has been distributed nationally.

There have been no reported illnesses associated with the consumption of this product.

CFIA always says that, and then sometimes changes its tune.