E. coli (Escherichia coli 0157:H7) Infection

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E. Coli Infection Facts

  • 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 stool 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 from 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.

What Is E. Coli?

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 their 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. These 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 on Other 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). These terms are likely to be modified as researchers discover new strains.

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.

What Causes E. Coli 0157:H7 Infection?

As mentioned above, only a small number (10–100) of organisms are required to cause disease in humans. Therefore, healthy people can become infected even if the contaminated food contains only a low number of E. coli 0157:H7. Almost all other EEC E. coli strains require a much higher number (thousands to millions) of ingested organisms to cause disease. Researchers have suggested several reasons why E. coli 0157:H7 is so aggressive. The bacteria can produce two types of toxins, termed Shiga (Stx 1 and Stx 2, also termed Vero toxins) toxins. These toxins are almost identical to the toxins produced by Shigella spp. and are capable of killing human intestinal cells by disrupting their protein synthesis. When the cells die, intestinal function is disrupted and intestinal bleeding can occur. The toxins and the damage that occurs to the intestines can lead to kidney damage, anemia, platelet aggregation, and death.

In addition, researchers suggest that the pili (fimbriae) of these organisms provide an adhesive receptor that is specific for human intestinal cells. Although E. coli 0157:H7 has been isolated from many animal species (for example, cattle, goats, and sheep), it usually causes no problems in animals; however, animal feces and products like untreated milk can transmit the bacteria to humans. The CDC suggests that E. coli 0157:H7 strain is most likely responsible for the majority of "E. coli" outbreaks in the US.

e. coli picture

Shiga Toxin: E. coli 0104:H4

What is Shiga Toxin (E. coli 0104:H4)?

Escherichia coli (E. coli) bacteria are commonly found in the gut of humans and animals. Most strains of E. coli do not cause harm in the bowels, although they can cause infections if they spread to urine or blood. However, a few strains have acquired characteristics that allow them to attach to cells in the gut, invade the lining of the gut and/or produce toxins that cause damage or secretory malfunctions of gut cells. One such toxin, the "Shiga" toxin is capable of causing diarrhea that may be watery or bloody. Strains that produce Shiga toxin are also called 'STEC' strains. If an STEC strain also has acquired the ability to adhere to cells in the gut, it is referred to as an 'enterohemorrhagic E. coli' or EHEC. The most common EHEC is E. coli 0157:H7, but other variants exist, including the one that is causing the 2011 E. coli outbreak that originated in Germany.

What Are the Symptoms of E. coli 0157:H7 Infection?

The usual initial symptoms include

  • nausea,
  • vomiting,
  • stomach cramps,
  • gas,
  • loss of appetite,
  • diarrhea,
  • bloody diarrhea,
  • mild fever (about 100 to 101 F or 37.7 to 38 C).

Severe infections can cause symptoms that are more serious, such as

However, the majority of affected individuals do not develop severe infections, but develop symptoms between 3 and 5 days after ingesting contaminated food or fluid. Some develop the usual symptoms between 1 to 10 days.

The majority of affected individuals resolve the infection without antibiotics in about 5 to 7 days after the onset of symptoms. However, some people (about 10%) develop complications with severe infections (see complications section listed below) and require hospitalization.

When to Seek Medical Care for E. coli 0157:H7

Since nausea, vomiting, low-grade fever, and diarrhea are common symptoms of many diseases, many clinicians suggest that affected individuals should seek medical care if:

  • there are signs of dehydration (for example, decreased urination, dry mucous membranes), especially in children under 5 years of age and the elderly;
  • sustained fever over 101 F (37.7 C);
  • presence of blood in the stool;
  • known ingestion of E. coli 0157:H7 contaminated food or fluid or close contact with people known to have E. coli 0157:H7 infection;
  • any complication of E. coli 0157:H7 infection (see section below).

How Is E. Coli 0157:H7 Diagnosed?

The diagnosis is usually made by an accurate history, physical exam, and analysis of the fecal sample. A presumptive diagnosis is made if the patient's history indicates an association with persons, foods, or fluids known to contain E. coli 0157:H7. Such a presumptive diagnosis is often made during outbreaks of the disease.

Culture of E. coli 0157:H7 from a fecal specimen on selective media (sorbitol-MacConkey agar) gives a definitive diagnosis of the infection when clear-appearing colonies react with 0157 antiserum. Other tests include PCR and immunofluorescence tests. The CDC has recommended that all patients being evaluated for community-acquired diarrhea should have their stool samples analyzed by immunologic test systems that detect all types of Shiga toxins as this test will likely detect almost all bacteria that produce Shiga toxins, especially the E. coli 0157:H7 strains. The CDC suggests that this test is even better than bacterial culture techniques, but recommend that both culture and immunologic tests should be done at the same time.

What Is the Treatment for E. Coli 0157:H7?

Most people require no treatment since many infections are self-limited. However, the main treatment is hydration, in the form of either oral or intravenous hydration. Several studies suggest that antibiotics should not be used because they lead to a more severe disease. This increase in severity is believed to be related to the damaging effect of the antibiotic on the bacteria, causing the damaged bacteria to release more toxins. The use of antibiotics has been reported to markedly increase the incidence of HUS (17-fold). Investigators suggest antibiotic use only if the patient is septic (high fever, high white blood cell count, low blood pressure, and decreased function of heart, kidneys, and/or brain.

What Home Remedies Soothe the Symptoms of E. coli 0157:H7?

In general, the majority of E. coli 0157:H7 infections are self-limited and require no treatment. However, the person should stay well-hydrated with oral fluids; if this is not possible, medical care should be obtained. In addition, investigators caution people not to use left-over antibiotics or other medicines such as atropine and diphenoxylate (Lomotil) as these may worsen the disease and trigger complications.

What Are the Complications of E. Coli 0157:H7?

About 10% of all persons infected with E. coli 0157:H7 develop some complication. These complications may lead to disability or death. The major complications are as follows:

  • Hemorrhagic (bloody) diarrhea: This complication can prolong the disease by about a week, and cause severe abdominal pain. The individual may also develop dehydration and anemia.
  • Hemolytic-uremic syndrome (HUS): This condition also prolongs the disease, as it usually becomes apparent about 7 to 10 days after the onset of symptoms. Children under 10 years of age are the most likely to get this complication. HUS is the most common cause of renal failure in children. The toxin produced by E. coli 0157:H7 enters the blood, causing blood cells to be damaged and small clots to form. The toxin can lodge in the kidneys and eventually destroy renal tissue. Sometimes the damage is severe enough to cause kidney failure.
  • Thrombotic thrombocytopenic purpura (TTP): This complication is a variation of HUS that usually occurs in the elderly. The same mechanisms as those for HUS are responsible for TTP. However, the elderly develop more clotting problems and use up more platelets resulting in easy or "spontaneous" bruising over the body. The elderly experience more fever and neurologic changes, in addition to kidney damage. Until the 1980's, TTP was considered a fatal disease. However, treatment with plasma exchange and infusion techniques has reduced the mortality rate (deaths) to about 10%.

How Can I Protect Myself from Getting E. Coli 0157:H7?

There usually are several outbreaks of food poisoning every year due to E. coli. A recent outbreak occurred in a restaurant chain located in two states (Washington and Oregon). The chain Chipolte, decided to temporarily shut down 43 locations because of about 22 people developing the infection. This is Chipotle's third outbreak in one year. Companies need to follow strict guidelines for food preparation. The following guidelines on preventing E. coli 0157:H7 are recommended by the CDC:

  1. Wash hands thoroughly after using the bathroom or changing diapers and before preparing or eating food. Wash hands after contact with animals or their environments (at farms, petting zoos, fairs, even your own pets in your own yard).
  2. Cook meats thoroughly. Ground beef and meat that has been needle-tenderized should be cooked to a temperature of at least 160 F/70 C. It's best to use a thermometer, as meat color is not a very reliable indicator of "doneness."
  3. Avoid raw milk, unpasteurized dairy products, and unpasteurized juices (like fresh apple cider).
  4. Avoid swallowing water when swimming or playing in lakes, ponds, streams, swimming pools, and backyard "kiddie" pools.
  5. Prevent cross contamination in food preparation areas by thoroughly washing hands, counters, cutting boards, and utensils after they come in contact with raw meat.

One of the major sources of outbreaks is hamburger meat contaminated with E. coli 0157:H7. Such infections have been termed "hamburger disease." Many authors recommend that hamburgers ordered in a restaurant should be "medium or well done", with no pink hamburger meat visible in the middle of the burger. Any "pink" hamburger meat should be cooked until brown to reduce the chance that viable E. coli are still present.

In addition, any food or liquid involved in a recall due to possible E. coli contamination should be disposed of immediately. In 2010, the FDA recalled several productions of beef, including material put into dry pet foods due to contamination with this organism.

What Is the Prognosis for Someone Infected with E. Coli 0157:H7?

People with E. coli 0157:H7 infection usually (about 90%) have a self-limited disease and the outcome is excellent. However, the prognosis worsens with the development of complication(s). Good hydration lessens the chances of complications and improves the outcome.

Individuals who develop hemorrhagic diarrhea and are treated promptly have better outcomes with reduced hospitalization. Complications such as HUS and TTP have a wide range of prognosis from good to poor, depending on the overall health of the individual and how quickly the complications are diagnosed and treated. For example, some individuals can recover completely, but others may require IV fluids, plasma exchange, plasma infusion, or dialysis, and may have end-organ failure (usually kidney failure) and neurologic problems. A few (about 10%) of TTP patients will die. Although infrequent, relatively healthy children and adults have died from E. coli 0157:H7 infections due to dehydration.

E. coli 0104:H4 Infections Originating in Germany

E. coli strain (0104:H4) is similar to the 0157:H7 strain. In the spring of 2011, the E. coli 0104:H4 strain was identified in Germany and was documented in 15 European countries. In most people, exposure to the infection occurred in Germany, most likely when they ate contaminated food (salads). The strain has been identified as E. coli 0104:H4 (also termed STEC 0104:H4).

E. coli 0104:H4 seems to exhibit some of the worst overlap features in the diseases caused by ECC group members. For example, E. coli 0104:H4 is reported to contain about 93% of E. coli 0157:H7 genetics and produces the Shiga (Vero) toxin and many patients (about 30%) developed HUS. However, it also seems to have the ability like EAEC strains to attach to the gastrointestinal cells. The outbreak was one of the largest ever reported for E. coli (4,075 infected patients) and was the most lethal (50 deaths). In addition, most strains isolated were resistant to multiple antibiotics (aminoglycosides, macrolides, and Beta-lactams).

The source of the infection was considered to be contaminated bean sprouts and other seeds grown organically and then shipped to many German restaurants. One major difference in E. coli 0104:H4 from other E. coli that cause HUS (mainly E. coli 0157:H7) is that the organism causes HUS in adults, particularly young adult females. Usually, HUS caused by E. coli 0157:H7 is seen in children, the elderly, and the relatively not healthy adults. This strain caused 908 infections complicated by HUS.

The diagnosis, treatment, prognosis, prevention, and complications are very similar to those listed in this article for E. coli 0157:H7.

The most recent guidelines from the CDC are as follows:

The strain of E. coli O104:H4 causing the outbreak is resistant to many antibiotics, because it has many genes that code for that resistance. Since CDC doesn’t recommend that STEC infections be treated with antibiotics, the fact that this strain is antibiotic resistant is not likely to impact the care that sick people receive. The presence of these genes simply means that the bacteria were likely, at some point in the past, to have been in environment with antibiotics in it.  Other bacteria occur with this level of resistance.  There is no reason to think that this strain has been modified intentionally to be antibiotic resistant.

Guidelines to ensure as complete as possible detection and characterization of STEC infections include the following:

  • All stools submitted for testing from patients with acute community-acquired diarrhea should be cultured for STEC O157:H7. These stools should be simultaneously assayed for non-O157 STEC strains with a test that detects the Shiga toxins or the genes encoding these toxins.
  • Clinical laboratories should report and send E. coli O157:H7 isolates and Shiga toxin-positive samples to state or local public health laboratories as soon as possible for additional characterization.
  • Specimens or enrichment broths in which Shiga toxin or STEC are detected, but from which O157:H7 STEC isolates were not recovered, should be forwarded as soon as possible to a state or local public health laboratory so that non-O157:H7 STEC strains (including STEC 0104:H4) can be isolated.
  • Often, by the time a patient presents with HUS, the causative STEC can no longer be easily isolated from a stool specimen. For any patient with HUS without a culture-confirmed STEC infection, stool can be sent to a public health laboratory or to the CDC through their public health laboratory for immunomagnetic separation (IMS) techniques that can increase the sensitivity of culture. In addition, with prior approval, serum can be sent through a state public health laboratory to the CDC for serological testing for antibodies to some STEC serogroups.

The benefits of adhering to the recommended testing strategy include early diagnosis, improved patient outcome, and detection of all STEC serotypes.

All patients with Shiga toxin-positive diarrheal illness or HUS should be reported to health departments.

Other Enterohemorrhagic E. coli Strains (for example, 0145, 026:H11)

Most enterohemorrhagic E. coli (EHEC or STEC) infections were thought to be variants of strain 0157:H7, however, enterohemorrhagic serotypes are not limited to the 0157:H7 serotype. Apparently, many other serotypes such as 0145 can acquire the plasmid that is responsible for the synthesis of Shiga (Vero) toxin, and thus can produce almost identical symptoms produced by 0157:H7 in infected humans. Consequently, these other E. coli serotypes can cause outbreaks of bloody diarrhea with hemorrhagic colitis that can become complicated by hemolytic uremia. In 2012, strain 0145 caused 18 infections and one infant death. Another strain, E. coli 0121 infected 19 persons in 2014; the strain produced a Shiga toxin. The source of the bacteria was raw clover sprouts.

These other E. coli serotypes produce essentially the same type of disease as 0157:H7 and are diagnosed and treated in the same manner. For all practical purposes, 0157:H7 represents all the other EHEC serotypes.

Reviewed on 12/28/2017

Medically reviewed by Robert L. Cox, MD; Board Certification Internal Medicine/Infectious Disease

REFERENCES:

CDC.gov. Multistate Outbreak of Shiga Toxin-producing Escherichia coli O145 Infections.

CDC.gov. Escherichia coli O157:H7.

CDC.gov.. Recommendations for Diagnosis of Shiga Toxin--Producing Escherichia coli Infections by Clinical Laboratories.

MedscapeReference.com. Hemolytic Uremic Syndrome.

Kumarasamy, K.K. et al. Emergence of a new antibiotic resistance mechanism in India, Pakistan, and the UK: a molecular, biological, and epidemiological study. The Lancet, published online Aug. 11, 2010. (NDM)

Pitout, J.D.D. The latest threat in the war on antimicrobial resistance. The Lancet, published online Aug. 11, 2010.

Textbookofbacteriology.net. Pathogenic E. coli.

U.S. Food and Drug Administration. BBB - Escherichia coli O157:H7 (EHEC).
 

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