E. coli O157:H7 – The Latest Pathogen Involved in a Multi-state Outbreak

E.Coli Bacteria
E.Coli Bacteria


E.coli 0157:H7 is the most common STEC (Shiga-toxins producing E. coli) in North America and can be found in a variety of food products, including meats, nuts, vegetables and dairy products. A recent outbreak of E. coli O157:H7 in the United States prompted the voluntary recall of two products, but the source of the outbreak is yet to be confirmed.

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Each year, there are 73,000 illnesses caused by E. coli O157:H7 in the United States. Since November, the CDC, the U.S. Food and Drug Administration (FDA), the U.S. Department of Agriculture Food Safety and Inspection Service, and public health officials in many states have been investigating an E. coli O157:H7 outbreak that has infected 19 people from 7 states. In response to the outbreak, Costco voluntarily recalled their rotisserie chicken salad (November 23, 2015) and Taylor Farms Pacific recalled 71 of their celery products (November 26, 2015).  However, follow up investigations have failed to confirm the presence of E. coli O157:H7 in the chicken salad at Costco, nor the ingredient responsible for the outbreak.

E. coli O157:H7 is the most common STEC in North America

There are over 100 enterohemorrhagic E. coli serotypes that produce Shiga or Shiga-like toxins (Shiga-toxins producing E. coli (STEC)). E. coli O157:H7, the culprit involved in the latest outbreak, is the most common STEC in North America. Compared to other pathogenic strains of E. coli that requires 106-108 CFU to infect, 10-100 CFU of E. coli O157:H7 is enough to cause an infection.

Undercooked hamburgers, ground beef, cheese, lettuce, spinach, bologna, frozen pizza, and hazelnuts have all been linked to previous E. coli O157:H7 outbreaks. Once ingested, E. coli O157:H7 grows in the large intestines, attaches to the intestinal wall, and produces toxins that can damage the mucosal and vascular endothelial cells. After the gastrointestinal barrier has been breached, the toxins gain entrance into the circulatory system and can travel to other host tissues, including the kidneys. Symptoms, which usually appear 3-4 days after infection but can appear from 1-10 day after an infection, include severe cramps, bloody diarrhea, and sometimes fever. People of all ages can be infected with E. coli O157:H7. However, children and the elderly are the most vulnerable to severe complications, such as hemolytic-uremic syndrome (HUS).

HUS is a life-threatening condition that affects 2-7% of infected individuals, primarily children under 5 and the elderly. Onset of HUS occurs 5-10 days after the start of diarrhea. HUS is characterized by red blood cell destruction, acute renal failure, and low platelet count. Damaged red blood cells can clog the kidney filtration system, potentially leading to kidney injury and failure. Many children with HUS require dialysis and some have long-term kidney problems that may require a kidney transplant. Other complications of HUS include brain damage, pancreas damage that may lead to diabetes, development of irritable bowel syndrome, and death. Mortality rate in children with HUS is 5-10%.

There are very few treatment options for an E. coli O157:H7 infection. In most cases, symptoms clear up on their own without any long-term effects. Antibiotics are not prescribed because they do not help clear the infection, nor alleviate symptoms and may potentially increase the risk of developing HUS. Aside from monitoring the symptoms, rest, and drinking plenty of fluids, there is no specific treatment option.

Preventative measures for avoiding an infection with E. coli O157:H7 include:

  • Cleaning and sanitizing all surfaces to avoid cross contamination with raw and cooked meat,
  • Using a meat thermometer to check that cooked meat has reached a safe internal temperature (ideally 70°C/160°F)
  • Drinking pasteurized milk
  • Washing fruits and vegetables

In addition, the following precautions should be taken to limit the spread of infection:

  • Ensure that the stools of infected individuals are disposed of properly
  • Do not allow children to share bath water with others that have signs of diarrhea
  • Avoid drinking and playing in non-chlorinated water
  • Wash hands thoroughly with soap and water

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Dr. Uyen Nguyen
After completing her B. Sc. in Biochemistry and Biomedical Sciences, she stayed at McMaster University to pursue a Ph.D. where she studied the effects of small-molecules on Listeria monocytogenes biofilm development in collaboration with the CFIA. Following a brief stint as a Post-doc, she is currently a R&D Microbiologist at a pharmaceutical company and a Freelance Academic Proofreader for Crimson-Enago. She has received numerous awards and scholarships including the Faculty of Health Sciences Graduate Programs Outstanding Thesis Awards, Ontario Graduate Fellowship, Fred and Helen Knight Enrichment Award. Outside of science, she loves travelling and exploring new places as well as creating and experimenting with desserts.