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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. There are many strains of E. coli bacteria and most of them are harmless. However, strains that produce Shiga toxin (such as E. coli O157:H7) can cause serious illness in people.

Symptoms appear 1 to 10 days after exposure (usually within 2 - 4 days), and include: diarrhea (which often becomes bloody) and stomach cramps, with little or no fever. STEC infections are diagnosed by doing special tests on a stool sample from an ill person.

Antibiotics are not recommended for STEC infection because they can increase the risk of hemolytic uremic syndrome (HUS), a serious complication that damages the kidneys and blood vessels. Most cases of STEC don't develop HUS, which is more common in young children and the elderly.

Shiga toxin-producing E. coli (STEC) can spread through undercooked ground beef and other beef products; unpasteurized milk, cheese, and juice; contaminated raw fruits, vegetables, and herbs; water contaminated with animal feces; and direct contact with farm animals or their environment. Ready-to-eat foods can also be contaminated 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 within households, child day-care centers, and long-term care facilities. Transmission is facilitated by inadequate handwashing 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:

Seventy cases of Shiga toxin-producing Escherichia coli (STEC) were reported in 2012. Twenty-three (33%) cases were E. coli O157 and 47 (67%) were non-O157 strains of STEC. The most common non-O157 serotypes were O26 (16), O103 (9), and O111 (9). Non-O157 case reports have increased in recent years due to newly available laboratory tests that identify these strains. 2012 was the first year that non-O157 case reports exceeded O157 reports.

Eleven of the patients (16%) reported in 2012 were hospitalized; two had hemolytic-uremic syndrome (HUS) and one required kidney dialysis. The rate of hospitalization of STEC cases has decreased in recent years as non-O157 infections, which cause milder illness, have become more common.

Eleven cases (16%) reported travel outside of the United States during their exposure period; seven of these cases traveled to Mexico.

Each year in Washington state there are 150 to 300 cases reported, with most cases occurring in the fall and summer. In 2012, one Washington resident was linked to a multi-state outbreak associated with sprouts served on sandwiches from a popular fast food chain.

Shiga toxin-producing E. coli cases by O antigen

For King County health care providers: