Also, it usually doesn't state on the package where it's from so that's another concern.
Most likely California’s huge Imperial Valley which borders Mexico.
Treating ground beef as an industrial commodity processed by an illegal alien workforce gave us the first E.coli outbreaks of years ago. That’s largely in the past but it left me with zero faith in America’s food processing industry.
This lettuce borne E.coli is just one more example what can happen when “economic efficiency” is given more priority than food safety. I suppose your best bet is only buying lettuce that is grown by hydroponics.