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Public Health - Seattle & King County

Shiga toxin-producing E. coli (STEC) including E. coli O157:H7

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

Symptoms typically appear 1 to 8 days after exposure (usually within 2 - 4 days) and include: diarrhea (which often becomes bloody) and stomach cramps, with mild or no fever. STEC infections are diagnosed by doing special tests on a stool sample from an ill person.

Infection with Shiga toxin-producing E. coli (STEC) can occur through consumption of: undercooked ground beef and other beef products; unpasteurized milk, cheese, and juice; contaminated raw fruits, vegetables, 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. Large multi-state outbreaks involving commercially distributed food products including beef, produce, and cheese have occurred in recent years.

Person-to-person transmission of E. coli can occur through the fecal-oral route, including transmission within households, childcare centers, and long-term care facilities. Transmission is facilitated by inadequate hand washing after a bowel movement and contamination of objects in the environment.

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Shiga toxin-producing E. coli in King County

Purpose of surveillance:

  • To identify outbreaks
  • To facilitate prompt and accurate diagnosis of cases
  • To identify other exposed persons requiring medical evaluation or monitoring and/or treatment
  • To implement disease control measures to prevent spread of the infection
  • To identify and eliminate sources of transmission including contaminated food and water

Shiga toxin-producing <i>E. coli </i> cases

Local epidemiology:

Seventy-four laboratory-confirmed and fourteen probable cases of Shiga toxin-producing Escherichia coli (STEC) were reported in 2014. This is the highest number of cases reported in the past ten years, in part due to a large child care-associated outbreak, as well as to an increased use of more sensitive culture-independent laboratory tests (CIDT) to diagnose cases. Among laboratory-confirmed STEC cases, twenty-one (28%) were E. coli O157, and 53 (72%) were non-O157 strains. The most common non-O157 serotypes were O26 (22), O103 (7), and O121 (7). Non-O157 STEC reports have increased in recent years due to newly available laboratory tests that identify these strains. 2014 was the third year that non-O157 case reports exceeded O157 reports.

Thirteen of the patients (15%) reported in 2014 were hospitalized, six of whom were children under age 13. There were no cases of hemolytic uremic syndrome (HUS), damage to the kidneys that can result from STEC infections. On average, King County receives zero to one report of HUS per year.

Fifteen cases (17%) reported travel outside of the United States during their exposure period; ten were associated with travel to Latin America. Of the cases reporting travel outside of the United States, all but two were non-O157 serotypes. Two cases were associated with a multi-state E. coli O157 outbreak linked to a resort hotel in Hawaii.

In June 2014 twelve laboratory-confirmed and thirteen epidemiologically linked cases were related to an outbreak of E. coli O26 at a child care center. Public Health worked with the child care to strengthen hygiene practices and control the spread of infection.

Four cases of E. coli O121 were part of a multistate outbreak caused by consumption of raw clover sprouts. Nineteen cases in six states were identified from May 1 - May 20, seven (44%) of whom were hospitalized. Eighty-one percent of interviewed cases reported consuming clover sprouts from various locations, all of which were traced back to a common sprout farm in Idaho. An investigation by the U.S. Food and Drug Administration (FDA) found nine violations in Good Manufacturing Practice (GMP), and all implicated products were removed from the market.

The city of Mercer Island issued two boil water advisories in September and October, after Seattle Public Utilities detected the presence of E. coli during routing water sampling. Although Public Health conducted enhanced surveillance, no cases of E. coli from this exposure were identified.

Each year in Washington state between 150 and 250 E. coli cases are reported, with most cases occurring in the fall and summer.

Shiga toxin-producing <i>E. coli </i> cases by O antigen

For King County health care providers: