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Marler Blog Providing Commentary on Food Poisoning Outbreaks & Litigation

So, what the heck is E. coli O157:H7?

Over the last several weeks I have been asked dozens of times about the origin of E. coli O157:H7 and the impacts upon people.  I remembered an article written on January 6, 1998 By Gina Kolata of the New York Times entitled: Detective Work and Science Reveal a New Lethal Bacteria

I have taken the liberty to excerpt some answers to the questions:

So, what the heck is E. coli O157:H7?

Normally, Escherichia coli bacteria live innocuously in the intestines of people and animals. But E. coli O157:H7 can cause diseases from standard diarrhea to kidney failure and death. The bacteria still befuddle medical doctors, who have misdiagnosed their infections as everything from appendicitis to blocked blood vessels of the colon. Once someone is infected, there is no effective medical treatment to combat the disease, and all doctors can do is prevent dehydration, wait for the disease to run its course, and hope for the best.

What illness does it cause?

However the toxin does its work — and scientists still do not know for sure — the result is that it can injure cells that line blood vessels, plugging them with blood clots. When this happens, the first symptom is bloody diarrhea. But a small proportion of people, especially young children and the elderly, develop hemolytic uremic syndrome, the actual destruction of the kidneys that occurs when blood vessels in these organs are destroyed. The syndrome can lead to kidney failure or can be fatal. Infections with E. coli O157:H7 are now the leading cause of kidney failure in children, the disease control centers says, with at least 1,000 children a year developing kidney failure from these infections, and 3 percent to 5 percent of them dying.

Older people also tend to develop another complication, thrombotic thrombocytopenic purpura, a sort of leakage of the blood vessels that feed nerve cells. The result is an encephalitis-like disease, with psychosis, comas or seizures.

The bacteria are surprisingly tough and virulent. For example, said Dr. Marguerite Neill, chief of the division of infectious diseases at Brown University School of Medicine, most bacteria do not produce disease unless a person is exposed to millions of them. But as few as 10 or so E. coli O157:H7 can produce illness — far too few to see or smell.

Where did it come from?

In the 1980’s Dr. Alison O’Brien, a microbiologist at the Uniformed Services University of the Health Sciences in Bethesda, Md., examined the rogue E. coli, and sure enough, discovered that it had somehow taken on the Shigella toxin gene. Moreover, in many of the E. coli, that gene was slightly altered in a way that made the bacterium produce toxin even deadlier than the original toxin made by Shigella.

No one knows exactly how the Shigella toxin genes jumped to E. coli, but Dr. O’Brien has an educated guess. Viruses that infect bacteria can sometimes pick up a gene from one bacterium and carry it to another.

But if that was the seminal event, Dr. O’Brien said, it probably did not occur in the United States, where Shigella bacteria do not have the dangerous toxin gene. Shigella in Central America do have that gene, however, and in the 1970’s, that area was hit with a pandemic of Shigella dysentery. As the Shigella mixed with harmless E. coli in people’s intestines, or as it mixed with harmless E. coli that inhabited animal manure, a virus may have carried Shigella toxin genes to E. coli. The result would have been a strain that had never been seen before: the toxin-armed E. coli O157:H7.

So, why do Cows, Pigs, Sheep and Goats carry this nasty bug?

The NYT article did not answer the question on how Shiga-toxin E. coli jumped from humans to animals, but a 2003 study on the prevalence of E. coli O157:H7 in livestock at 29 county and 3 large state agricultural fairs in the United States found that E. coli O157:H7 could be isolated from 13.8% of beef cattle, 5.9% of dairy cattle, 3.6% of pigs, 5.2% of sheep, and 2.8% of goats.  A single cow produces about 30 kilograms (66 pounds) of manure per day. Each gram of manure can contain ten million (10,000,000) fecal coliform organisms, which could include E. coli O157:H7. A cow can put out about three hundred billion (300,000,000,000) fecal coliforms per day.

Fecal testing of dairy cattle worldwide showed wide ranges of prevalence rates for E. coli O157:H7 (0.2 to 48.8%) and non-O157 STEC (0.4 to 74.0%). The prevalence of E. coli O157H7 in beef cattle in Canada at the three different sites in the horizontal study varied from 2.5 to 45%. The point prevalence of E. coli O157 among Saskatchewan cattle from 20 different feedlots ranged from 0% to a high of 57%.

And cows are next to spinach fields because?