According to researchers Jonathan Klick and Joshua D. Wright, both hospital admissions and deaths from E. coli spiked in San Francisco almost immediately after the first phase of that city’s Plastic Bag Reduction Ordinance went into effect in October 2007. Deaths from E. coli-based food poisoning rose by nearly 50 percent almost immediately, with 34 percent more emergency room visits due to E. coli poisoning relative to nearby counties with no bag ban then in place.

The reason for the increased suffering after plastic bags were banned? According to Klick and Wright, a study in 2011 found that most people don’t launder their reusable grocery bags nearly enough, if at all. In that earlier study, which involved interviews of shoppers in California and Arizona, only three percent of respondents said they ever wash their reusable grocery bags, and that most people put raw meat — a major E. coli source — and vegetables in the same bags indiscriminately. Eight percent of bags tested were contaminated with coliform bacteria. Bags stored in car trunks proved even more likely to be contaminated: apparently the warm, dark environment there is ideal for culturing microbial nasties.

This isn’t the first time contamination of reusable bags has been a topic of conversation. One such bag was fingered as “patient zero” in an outbreak of norovirus among an Oregon soccer team in 2010, for instance. But despite the public health issues, it’s still a good idea to avoid plastic bags: they’re implicated in the deaths of hundreds of thousands of marine animal a year, and we use up 12 million barrels of petroleum just to keep the U.S. in disposable plastic grocery bags every year. California cities from Glendale to Mendocino have enacted bag bans for just that reason.

So how do we prevent a subsequent plague of E. coli? Klick and Wright offer a way out, suggesting that “fastidious washing of the bags can virtually eliminate the risks.”

In other words, get used to washing your grocery bags after each use.

Stay Safe USA!