Escherichia coli ( E. coli 0157:H7; 0157:H7) Infections

Escherichia coli Facts and Overview

• E. coli are gram-negative bacteria found worldwide; there are many subtypes of this bacterial species that cause a wide variety of diseases in humans; the bacteria can be transmitted person-to-person and by contaminated food and water.
• E. coli cause disease by invading tissues, by producing various toxins, by adhering to tissues and by forming aggregates or clumps of bacteria.
• Usual symptoms initially are nausea, vomiting, stomach cramps, and diarrhea; other symptoms that may occur are fever and bloody diarrhea, depending on the bacterial subtype.
• Seek medical care if a person has dehydration, sustained fever above 101 F (37.7 C), blood in stools or has ingested food or fluid known to be contaminated with E. coli strains that cause an outbreak of disease.
• Definitive diagnosis is made by immunological tests or by culturing the bacteria from the patient or patient's food or fluid source.
• Many patients need no treatment because the disease is usually self-limiting; however, patients with serious infections may require hospitalization.
• Complications, especially with E. coli 0157:H7 and a few other strains, can result in hemorrhagic (very bloody) diarrhea, kidney failure (termed hemolytic-uremic syndrome), thrombotic thrombocytopenic purpura (loss of blood platelets and kidney failure) and occasionally, death.
• Prevention of E. coli infections is done by:
  • using a good hand washing technique,
  • cooking meats thoroughly,
  • avoiding drinking raw milk and swallowing water from lakes, ponds, or swimming pools, and
  • avoiding contamination of other foods with raw meat by using cleaned utensils and preparation surfaces.
• Prognosis in about 90% of patients is excellent with complete recovery; people with complications have a wide range of outcomes from good to poor.

Escherichia coli (including E. coli 0157:H7) are gram-negative bacteria that are rod-shaped, have the ability to survive in aerobic and anaerobic environments (termed a facultative anaerobe), and may or may not produce flagella and pili (thin hair-like projections) depending on the environmental needs. E. coli strains are found worldwide and live in significant numbers in human and other animals as part of the normal bacterial population of the large intestines. The organisms have likely co-existed with humans for eons, but were first isolated by T. Escherich in 1885; the organisms were named after him. E. coli strains are one of the most frequent causes of several common bacterial infections, including cholecystitis, bacteremia, cholangitis, urinary tract infection (UTI), traveler's diarrhea, and other clinical infections such as neonatal meningitis, pneumonia, abdominal abscesses, and hemolytic uremic syndrome (HUS).

E. coli 0157:H7 belongs to a "group" of E. coli termed enterohemorrhagic E. coli strains (EHEC). These organisms may be named VTEC or STEC (see section onOther Enterohemorrhagic E. coli Strains). There are 4 to 6 "groups" of E. coli; these groups are roughly based on their ability to cause certain diseases and are listed below:

1. EHEC (enterohemorrhagic E. coli) – hemorrhagic colitis or hemolytic-uremic syndrome (HUS); additional terms for EHEC are VTEC and STEC which stand for Vero toxin-producing E. coli and Shiga toxin-producing E. coli, respectively.
2. ETEC (enterotoxogenic E. coli) - traveler's diarrhea
3. EPEC (enteropathogenic E. coli) – childhood diarrhea
4. EIEC (enteroinvasive E. coli) – Shigella-like dysentery
5. EAEC (enteroadherent E. coli) – childhood diarrhea, some cases of traveler's diarrhea
6. EAggEC (enteroaggregative E. coli) – persistent diarrhea in developing countries

These four to six groups together are also termed EEC (enterovirulent E. coli). As the reader can see, there are overlaps in disease syndromes and that is the reason why experts disagree on the actual number of the bacterial groups (EPEC, EAEC, and EAggEC or EACE and EAggEC are often lumped together). In addition, the newest E. coli strain, E. coli 0104:H4 has properties that distinctly overlap groups EPEC and EHEC (see section on E. coli 0104:H4).

The name E. coli 0157:H7 seems complex; however scientists use the numbers and letters to specifically designate small differences in E. coli strains. The 0157 is the "O" serotype antigen that identifies the E. coli strain (there are over 700 strains) and the H7 represents the antigen type on the bacterium's flagella. These designations are used to identify strains causing specific diseases and have been utilized to identify outbreaks of disease.

E. coli 0157:H7 is of specific interest to the Centers for Disease Control and Prevention (CDC) and physicians around the world because strains of this bacterium can be particularly virulent (deadly), even in relatively healthy individuals. Scientists have estimated that only about 10 – 100 organisms when ingested can cause disease; most other E. coli need about 10, 000 to over a million organisms to produce disease. This strain has caused many outbreaks of disease and investigators suggest that at least 70,000 infections occur per year in the US. This strain can result in up to 50% mortality in the elderly if the patients develop thrombotic thrombocytopenic purpura (TTP; blood platelet clotting and bleeding). Unfortunately, the bacteria are easily spread to people by contaminated food or liquids.