Jonathan Klick and Joshua Wright, who are law professors at the University of Pennsylvania and George Mason University, respectively, have done a more recent study on the public-health impact of plastic-bag bans. They find that emergency-room admissions related to E. coli infections increased in San Francisco after the ban. (Nearby counties did not show this increase.) And this effect showed up as soon as the ban was implemented. (“There is a clear discontinuity at the time of adoption.”) The San Francisco ban was also associated with increases in salmonella and other bacterial infections. Similar effects were found in other California towns that adopted such laws.