Maryn McKenna has a great update today on the E. coli situation, looking at where we are as far as unanswered questions about the outbreak and the strain. It’s been a messy day; more evidence seems to point to the sprout farm, but CIDRAP also notes that another contaminated cucumber was found in the compost bin of a family sickened by the bacterium (this one had the correct serotype–O104), but it’s impossible to tell at this point whether the cucumber was the source of that bacterium or it ended up there from one of the sickened family members. Twists and turns abound in this investigation. I’ve not seen any confirmation that the remaining sprout isolates tested negative yet, either.

One thing I want to emphasize and expand upon, from the CIDRAP article:

Most of the investigation findings point back to a sprout source, and microbiological testing a month after the fact doesn’t change that, Hedberg said. “Negative micro results cannot negate positive epi results. This is an important principle that we cannot state too strongly.”

At this late date, it’s hard to say whether we’ll be able to definitively trace this back to its source–too much time may have passed for there to be any remaining contaminated source material left. This means we might not ever find the “smoking gun” (or smoking sprouts, as the case may be). With such a severe outbreak–725 cases of hemolytic uremic syndrome, over a quarter of those infected–that’s bad news if we can’t confirm the vehicle, as it may make it more difficult to find the ultimate source of this strain. However, as Hedberg notes, we do still have the epi. This was used long before we had today’s molecular typing techniques, or even before we had microbiology culture ability, for that matter. Think John Snow’s cholera investigations, where he didn’t even know about bacteria and yet was able to determine the water as the vehicle for infection. So while confirmation may not happen, it’s still looking like most lines of evidence point to the implicated farm.

Maryn also brings up a great point that what we’re seeing as far as cases may be over-estimating the actual severity of the infection. I’ve talked about this previously regarding influenza infections, particularly H5N1. Right now H5N1 has a high mortality rate–but is it artificially high, because mild or asymptomatic infections are being missed?

With O104, as with any food-borne infection, surely this is happening. Mild diarrhea or stomach cramping isn’t something people frequently go to their healthcare provider over, so inevitably cases are missed. However, it probably happens with any E. coli outbreak, yet in most others we still see HUS rates between about 2-7% of the confirmed infections, while this one is at about 26%. So it doesn’t seem (to me, at least) that missed mild infections are the whole story. Is this acting like the novel Clostridium difficile strains, which have a mutation in a regulatory gene that leads them to pump out higher levels of toxin than “regular” strains? More than just genetic analysis will be needed to investigate that–some basic microbiology will also be needed. If nothing else, this outbreak has given us much research fodder over the coming years.

Comments

  1. #1 William Skyvington
    June 9, 2011

    An interesting non-technical PDF document from the Division of Agriculture and Natural Resources at the University of California, intended for folk who grow sprouts at home, draws attention to the fact that seeds of mung beans can be infected with pathogens well before they are transformed into sprouts in a clean controlled environment. Concerning the German organic farm that might be the source of the epidemic, I haven’t understood whether they purchase seeds from the outside world, or whether they use their own locally-grown seeds.

  2. “Right now H5N1 has a high mortality rate–but is it artificially high, because mild or asymptomatic infections are being missed?”

    A study was done years ago looking for mild cases in an area of high H5N1 human cases. None were found.

  3. #3 Tara C. Smith
    June 9, 2011

    Yeah, I blogged that at the time but also noted several limitations.

  4. #4 liz Reilley
    August 3, 2011

    Hi – I’m curious to hear from Tara smith about her position on sprouts in general … as long as rigorous food safety protocol is followed along with an extensive testing (hold and release) program. Miracle food? Or something that should be avoided, period.? or both? or neither… I’m looking for speakers for the 21st annual International sprout Growers Association in Las Vegas, October 18 – 21st.
    Also, is there any research on possible medicinal effects of various sprouts on C. Diff?

    thanks!
    Liz Reilley
    Jonathan Sprouts
    35 years of Sprouting
    617-406-9563

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