July 2, 2022

How Bacteria In Raw Milk Sickens Some But Not All Exposed

Raw milk has been the source of a number of recent foodborne illness outbreaks including two ongoing E.coli outbreaks in Missouri and Oregon that have sickened at least 18 people and hospitalized five small children with hemolytic uremic syndrome (HUS), which causes kidney failure.

Milk splashesRaw, or unpasteurized, milk products account for the majority of all dairy product-associated outbreaks of foodborne illness reported to Centers for Disease Control and Prevention (CDC). From 1973 to 2009, 82 percent of dairy-related outbreaks were caused by raw milk or cheese made from raw milk.

In the last 30 months, 27 raw milk outbreaks have sickened 409 people, according to reports from state health departments. There have been five raw milk outbreaks so far this year.

Although public health officials warn consumers not to drink raw, or unpasteurized, milk because of the dangerous pathogens it can contain, enthusiasts believe raw milk is natural and safe.

Food Poisoning Bulletin asked Heidi Kassenborg DVM, and director of the Minnesota Department of Agriculture’s Dairy and Food Inspection Division, and Joni Scheftel DVM, from the Minnesota Department Health to answer some questions that frequently come up during raw milk outbreaks.

Q: How can E.coli get into some, but not all bottles of milk when there is an outbreak?

A:  Cows are milked twice or even three times per day, with the milk collected in a bulk tank. With pathogens like E. coli 0157:H7, it only takes a small amount to cause big problems for human health. Further complicating matters is that fact that pathogens may not be evenly distributed within a tank of milk.  Bacteria do not get evenly distributed throughout a product.  They tend to group in clusters.  So milk taken from one part of the bulk tank may be contaminated while the rest is not.

Q:  Is fecal contamination on the udder the only way for E.coli to get into milk?

A:  In the case of Shiga-toxin producing Escherichia coli, contamination on the udder with cow manure is one of the primary ways for these bacteria to get into the milk.  Other ways that harmful bacteria can contaminate milk are through contaminated equipment and improper storage.

Q:  How much E.coli does it take to make a person sick?

A:  The infectious dose of E. coli is very low – it can be as low as 10 organisms.

Q:  How can members of one family all drink from the same bottle but not all get sick? 

A:  E. coli organisms may not be evenly distributed in the milk and they can multiply over time, so people drinking milk from the same bottle at different times can be exposed to different doses of infectious organisms. In addition, people vary in terms of the ability of their immune system to fight off infection. A person may have had an E coli infection previously (often in childhood) and be immune or partially immune to infection.

Generally, the very young, the very old, pregnant women and those with immune-compromising conditions or taking immune suppressing medications are more susceptible to E coli infection. That is another reason that you may see a spectrum of symptoms from mild (or no symptoms) to severe symptoms within a family group exposed to the same bottle of contaminated milk.

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