Reusable bags redux: dirty bags kill

The Internet is there to provide data for what you already believe.” That’s what Doug emailed me in a conversation we were having about the endless coverage of the supposed maim and chaos that reusable shopping bags have on public health.. The reusable-shopping-bags-are-killing-us discourse took a turn into the mainstream when the NY Post and San Francisco Chronicle covered a publishing-by-press-release paper by Jonathan Klick and Joshua Wright.

They also put their paper on the Internet, on the Social Science Research Network, carrying the tag line of U of Penn Inst for Law & Econ Research Paper. But not in a peer reviewed journal that deals with food safety, microbiology or public health.

Klick and Wright claim that something stinky has been going on since San Francisco banned plastic shopping bags, and the replacements, reusable polypropylene and or canvas bags, are killing people.

From the paper,

We examine the pattern of emergency room admissions related to bacterial intestinal infections, especially those related to E. coli around the implementation of the San Francisco County ban in October 2007. We find that ER admissions increase by at least one fourth relative to other California counties. Subsequent bans in other California municipalities resulted in similar increases. An examination of deaths related to intestinal infections shows a comparable increase.vector_skull_halloween_trick_or_treat_grocery_tote_bag-p1496283172805687032wl6f_325(3)(2)

Krick and White choose to report hospital room illnesses and deaths from pathogenic E. coli – and omit statistics on other pathogens – and it’s not clear why. In the Chronicle, San Francisco health officer Tomás Aragón calls the research sloppy. I’m with him.
Cited in the research note is a paper from Williams and colleagues (2011) who have published the only peer-reviewed study on the microbial safety of reusable bags. They sampled 58 bags taken from shoppers in Arizona and California, finding coliform in just over half.  And E. coli matters more than coliform (which is commonly found on plant material and is not a good indicator of pathogen presence on food). At least E. coli demonstrates that a pathogen might be there. The Williams study showed generic E. coli can float around in bags – they recovered it in 12% of what they sampled (n=58).

An unanswered question is, can E. coli or other bugs be (or is it likely) transferred to any ready-to-eat foods, or somehow to food contact surfaces in the home? Seems like that matters. Just because the bacteria might be there, doesn’t mean it can contaminate a ready-to-eat food. No one has presented data to support that. We’ve done some cross-contamination work in bags recently and although I’ll wait for the peer review, the data shows that transfer is pretty unlikely.

I don’t know what happened in Frisco (I hear the folks from there hate that) but my guess is it ain’t the bags. I also visited in San Francisco in 2007, which correlates (but doesn’t prove causation) with the onset of the start of the illnesses. Maybe it was something I left behind.

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About Ben Chapman

Dr. Ben Chapman is an associate professor and food safety extension specialist at North Carolina State University. As a teenager, a Saturday afternoon viewing of the classic cable movie, Outbreak, sparked his interest in pathogens and public health. With the goal of less foodborne illness, his group designs, implements, and evaluates food safety strategies, messages, and media from farm-to-fork. Through reality-based research, Chapman investigates behaviors and creates interventions aimed at amateur and professional food handlers, managers, and organizational decision-makers; the gate keepers of safe food. Ben co-hosts a biweekly podcast called Food Safety Talk and tries to further engage folks online through Instagram, Twitter, Facebook, YouTube and, maybe not surprisingly, Pinterest. Follow on Twitter @benjaminchapman.