That seems to be their point. Paraphrase: "Given what we all know about the (ahem) personal habits of San Franciscans, a little extra e.coli due to changing grocery bag usage wouldn't show up in the stats. Maybe they should run some numbers in communities where everyone doesn't, well, you know ..."
About 10 years ago, I tried listening to Michael Savage. I remember him complaining that the bum infestation was so bad, SF had started using chlorine in the street cleaners when washing down the bum-frequented areas of tourist district.
Can't remember what they were finding. Hepatitis, most likely.