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Shiga toxin-producing E. coli O157:H7 infections among adults in King County ― Unknown source

Cases 3
Hospitalizations 0
Deaths 0
Age range 18 to 36 years old
Status Investigation is complete
Location Unknown source
Range of dates reported October 4 – October 16, 2022

Highlights, updated May 24, 2023


Public Health investigated an outbreak of three people infected with Shiga toxin-producing E. coli O157:H7 (also known as STEC). Between October 4 – 16, 2022, 3 people from 3 separate households reported becoming ill. Sick people ranged in age from 18 to 36 years old. Symptoms reported included diarrhea and abdominal pain.

No source was identified. Two of the three sick people ate dishes that were prepared with raw or undercooked beef.

Confirmed cases were linked through genetic fingerprinting results (whole genome sequencing) which indicated that they have the same genetic strain, meaning they likely had a common source of infection.


All three people developed one or more symptoms consistent with STEC, including diarrhea (often bloody), abdominal cramping, nausea, and vomiting. Cases had illness onset dates from September 21 – October 12, 2022. All the cases were from separate households.

Public Health actions

Public Health conducted interviews with the people ill with STEC to identify any common exposures and provided guidance to help prevent further spread.

On November 2, 2022, Environmental Health Investigators visited two locations listed by some of the ill people as places they ate during their likely exposure period. Environmental Health Investigators took environmental samples (i.e., swabs) during the inspections and E. coli O157:H7 was not detected in the environmental samples.

Public Health worked with the United States Department of Agriculture (USDA) and Washington State Department of Health to complete environmental testing and a traceback investigation to identify points of contamination in the food supply chain. While a common beef supplier was linked to two of the cases, the source is unknown.

Laboratory testing

All the cases had confirmatory testing indicating infections with Shiga toxin-producing E. coli O157:H7 via culture. All confirmed cases had the same strain of Shiga toxin-producing E. coli O157:H7, based on genetic fingerprinting (whole genome sequencing or WGS) at the Washington State Public Health Laboratory.

About STEC

E. coli germs (bacteria) normally live in the intestines of humans and animals. Many strains of E. coli bacteria exist, and most of them are harmless or beneficial to human health. STEC are strains of E. coli that produce Shiga toxin (such as E. coli O157:H7) and can cause serious illness in people.

Infection with STEC can occur through consumption of undercooked ground beef and other beef products; unpasteurized (raw) milk, cheese, and juice; contaminated raw fruits, vegetables, sprouts and herbs; water contaminated with animal feces, or by direct contact with farm animals or their environment. Ready-to-eat foods can also be contaminated with STEC through contact with raw beef or raw beef juices in the kitchen.

STEC and other foodborne infections occur throughout the year but may increase during late spring and summer months.

Symptoms of STEC include diarrhea (which often becomes bloody) and stomach cramps, with mild or no fever. Illness typically lasts several days and people can spread infection to others even after symptoms resolve.

  • STEC infections usually resolve in 5-7 days but recovered individuals may still spread the bacteria. Up to one third of children may continue to shed STEC for as long as 3 weeks.
  • Around 5–10% of those who are diagnosed with STEC infection develop a potentially life-threatening complication known as hemolytic uremic syndrome (HUS). Clues that a person is developing HUS include decreased frequency of urination and feeling very tired. People with HUS should be hospitalized because their kidneys may stop working and they may develop other serious problems. Most people with HUS recover within a few weeks, but some suffer permanent damage or die.
  • Ill people with suspected STEC infection should not work in food handling, patient care, or childcare settings, and ill children with suspected STEC infection should not attend daycare until they have seen a healthcare provider and been tested for STEC infection, even if their illness is mild. People with STEC infections who work in or attend these sensitive settings must be cleared by Public Health before returning.


General advice for reducing risk of getting STEC:

  • Avoid eating high-risk foods, especially undercooked ground beef and other beef products, goat products, and sheep products, unpasteurized (raw) milk or juice or cheese, and raw sprouts.
  • Wash hands with soap and water before preparing food for yourself or your children, before eating food, after handling raw meats, after going to the bathroom or changing diapers, and after contact with cows, sheep, or goats, their food or treats, or their living environment.
  • If soap and water aren't available, use an alcohol-based hand sanitizer with at least 60% alcohol (check the product label to be sure). These alcohol-based products can quickly reduce the number of germs on hands in some situations, but they are not a substitute for washing with soap and running water.
  • Thoroughly wash fresh produce before eating.
  • If washing "pre-washed" or "ready to eat" produce items, be sure it does not come into contact with unclean surfaces or utensils.
  • Wash cutting boards and counters used for meat or poultry preparation immediately after use to avoid cross contaminating other foods.
  • Cook all meats thoroughly, especially ground beef. Use a food thermometer to make sure meats have reached a safe internal temperature.
    • Cook ground beef and pork to a minimum internal temperature of 160°F.
    • Cook beef steaks, beef roasts, goat, and lamb to an internal temperature of at least 145°F and allow to rest for 3 minutes after you remove meat from the grill or stove.

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