theodp writes: A paper by Wharton’s Jonathan Klick and Joshua Wright suggested that San Francisco’s eco-friendly ban on plastic bags might actually be killing people. Klick and Wright found that food-borne illnesses in San Francisco increased 46% after the bag ban went into effect in 2007, with no such uptick in neighboring counties. Most likely, the authors concluded, this was due to the fact that people were putting their food into dirty reusable bags and not washing them afterward. But Tomas Aragon, an epidemiologist at UC Berkeley and health officer for the city of San Francisco, begs to differ, arguing that in order to establish a link between the bag ban and illnesses, the authors would have to show that the same people who are using reusable bags are also the ones getting sick. Aragon offers an alternative hypothesis for the recent rise in deaths related to intestinal infections, noting that a large portion of the cases in San Francisco involve C. difficile enterocolitis, a disease that’s often coded as food-borne illness in hospitals which has become more common in lots of places since 2005, all around the U.S., Canada, and Europe (for yet-unexplained reasons). 'The increase in San Francisco,' he suggests, 'probably reflects this international increase.'