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There has been some excellent discussion to provide guidance to Marcie McBee, the Tennessee raw-milk farmer who had an outbreak of illness traced to E.coli O157:H7. 

What makes pieces of this discussion exciting is that it begins to lift the veil of silence that accompanies outbreaks linked to raw milk. Because the public health community tends to operate under the assumption raw milk is inherently unsafe, it doesn’t seek to offer specific insights and potential solutions to farmers who must deal with the challenges of providing a healthy product. 

The Raw Milk Institute (RAWMI) has pioneered this process of producer education, and has a number of programs ongoing on various aspects of reducing risk associated with pathogens. 

I encourage further lifting of this veil, and to help in that effort, I am re-posting a couple of the important comments on how raw dairies can begin to approach dealing with E.coli O157:H7. This from Dr. Cat Berge, a veterinarian and member of the RAWMI board of directors: 

I am a veterinary epidemiologist and Board of Director of the Raw Milk Institute. We work very hard to educate our raw milk listed dairies about hazards in milk and how to ensure that raw milk is safe. Unfortunately, the situation is not as simple as you have come to understand. I believe you have not not totally understood the complexity of E. coli O157:H7 in dairy farms. 

There is a wide variability in E. coli O157:H7 shedding within and among dairy farms and the complexity of control at the farm level is high. (Edrington et al., 2004) E. coli O157:H7 is not only present in the cow feces. It has been identified in various locations on dairies such as feed, wild birds, pets, water. Strains can persist in a herd for more than two years. (Shere et al., 1998). Animal-to-animal and waterborne dissemination of E. coli O157:H7 is common and effective water treatment to reduce the spread of this pathogen in cattle is needed. (Shere et al., 2002). Heifers and calves are much more likely to shed E. coli O157:H7 and therefore simply monitoring the lactating cows is not sufficient to rule out the presence of the bacteria on the farm. (Cobbold and Desmarchelier, 2000; Stanford et al., 2005).

Some cattle may be ‘super-shedders’ of the bacterium. Super-shedders may be excreting >1000 to 10,000 bacteria/gram feces. Super-shedders have been found to constitute a small proportion of the cattle in a feedlot (<10%) but they may account for >90% of all E. coli O157:H7 excreted. Although super-shedders may account for a high level of infection, there is no such simple solution as if that cow walks away, every bacteria is gone. Low level shedding can be very intermittent, and therefore a negative sample does not mean that the bacteria is no longer there. (Robinson et al., 2004)

As I always repeat to our listed farmers when I talk about diagnostic or screening samples, there is a simple rule: A negative sample does not necessarily mean that the bacteria is not there!! Just remember this sentence and this will help you understand a lot about sampling and detecting bacteria. (References available in original post.)

Marcie McBee inquired further: 

From my understanding different cows will shed each month but you will have at least one persistent shedder cow that will shed all the time. She if the “sick cow” is removed, then the others will shed it and then have to pick it up from somewhere else (as you say through other animals or water). Maybe this does not eradicate it off the farm but it should show it to not be in the cows. The persistent shedder cow will test positive every time. (Making this strain easier to find in stool rather than in milk ?)

Dr. Berge answered:

I wish it was that simple. But bacteria are not proprietary to an animal. They can be seen as passengers on a bus, they come and go. Some are regulars, some are sporadic. Some use other methods of transportation. Some hang out in pools… that is their favorite Residence, other camp out in manure, feed or take a ride on a car wheel or your hands. The key is to realize that you can not just test and when you have all negative results, that you are somehow safe and free. The supershedders are a problem, but the ecology of the bacteria is not simply explained by the existence of a supershedder. 

Shawn Barr offered a RAWMI producer’s perspective to McBee: 

The RAMP plan as recommended by RAWMI is a holistic plan. It doesn’t address just one thing. Rather, its starts by assessing the various potential risks on YOUR specific farm, and then building your management plan around those issues. It is highly individualize. Before you can do that though, you need to understand some basic bacteriology, so you are definitely asking the right questions! 

If you want to talk a look as how the various RAWMI producers have assessed and minimized their risks, take a look at the rawmilkinstitute.net website. Under listed farms, each farm’s plan is available for public view.