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Public Health - Seattle & King County

Shiga toxin-producing E. coli (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 10 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, child day-care 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 E. coli cases

Local epidemiology:

Sixty-nine laboratory-confirmed and two probable cases of Shiga toxin-producing Escherichia coli (STEC) were reported in 2013. Twenty-six (27%) STEC cases were E. coli O157, and 43 (73%) were non-O157 strains. The most common non-O157 serotypes were O26 (14), O103 (13), and O111 (4). Non-O157 STEC reports have increased in recent years due to newly available laboratory tests that identify these strains. 2013 was the second year that non-O157 case reports exceeded O157 reports.

Twenty-one of the patients (30%) reported in 2013 were hospitalized, 11 of whom were children under age 13. Three HUS cases were reported in children aged 18 and younger. On average, King County receives 0 – 1 report of HUS per year.

Twelve cases reported travel outside of the United States during their exposure period; seven were associated with travel to Mexico and one was a household contact to an international-travel-acquired case. Of the cases reporting travel outside of the United States, all but one were non-O157 serotypes.

Three E. coli O157:H7 cases were linked to eating at the same restaurant within a two-week period. The investigation of the restaurant revealed multiple violations which may have contributed to cross-contamination and unsanitary conditions. Of note is that two of the three cases were vegetarian. Although in the past E. coli has generally been associated with exposure to contaminated meat (particularly beef), recent years have seen an upsurge in infections related to fruits and vegetables, which can become contaminated at several points in the food chain.

Each year in Washington state 150 to 300 cases are reported, with most cases occurring in the fall and summer.

Shiga toxin-producing E. coli cases by O antigen

For King County health care providers: