Escherichia coli 0157:H7 infection

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E. coli 0157:H7 Facts

  • E. coli 0157:H7 is a gram-negative bacterium that can produce a bloody diarrhea due to toxins it secretes when it infects human intestinal tracts.
  • The symptoms of E. coli 0157:H7 infection may include a low fever, nausea, vomiting, stomach cramps, and bloody diarrhea.
  • E. coli 0157:H7 is notorious because it can cause additional complications in children and the elderly; renal failure, anemia, and dehydration especially for children (termed HUS or Hemolytic-uremic syndrome) and spontaneous bleeding, organ failures, and mental changes in the elderly (termed TTP or thrombotic thrombocytopenic purpura). Some of these patients develop disabilities or die.
  • Diagnosis is definitively made when E. coli 0157:H7 is isolated, usually from the patient’s stool, and identified as serotype 0157 by immunologic tests.
  • Most E. coli 0157:H7 infections resolve spontaneously and require no treatment; however supportive treatment is usually quickly required if the patient becomes dehydrated, anemic, or develops HUS or TTP.
  • The majority of E. coli 0157:H7 infections have excellent outcomes. If complications develop such as severe dehydration, anemia, HUS or TTP, the outcomes can decline from good to poor quickly.
  • Prevention consists of eating well cooked foods, especially hamburger, and drinking treated or pasteurized fluids. Avoiding touching or eating any food that may be contaminated with any animal or human waste will help prevent the infection.
  • There is no E. coli 0157:H7 vaccine available for humans.

What is E. coli?

Escherichia coli (E. coli) are gram-negative bacteria that can survive in an environment with or without air (facultative anaerobes) and, depending on the environment, may or may not produce thin hair-like structures (flagella or pili) that allow the bacteria to move and to attach to human cells. These bacteria commonly live in the intestines of people and animals worldwide. There are many strains (over 700 serotypes) of E. coli. Most of the E. coli are normal inhabitants of the small intestine and colon and do not cause disease in the intestines (non-pathogenic). Nevertheless, these non-pathogenic E. coli can cause disease if they spread outside of the intestines, for example, into the urinary tract (where they cause bladder or kidney infections), or into the blood stream (sepsis). Other E. coli strains (enterovirulent E. coli strains or EEC) cause “poisoning” or diarrhea even though they usually remain within the intestine by producing toxins or intestinal inflammation. There are four to six groups (some researchers combine groups) of E. coli strains that comprise EEC.

  • EHEC (enterohemorrhagic E. coli)
  • ETEC (enterotoxigenic E. coli)
  • EPEC (enteropathogenic E. coli)
  • EIEC (enteroinvasive E. coli
  • EAEC (enteroadherent E. coli
  • EAggEC (enteroaggregative E. coli)

E. coli were first isolated by T. Escherich in 1885 and were named after him. The over 700 serotypes are identified by small antigenic changes in their surface “O” antigens (lipopolysaccharides or molecules on the bacterial surface of gram-negative bacteria), for example E. coli 0157 or E. coli 055. These serotypes are identified by immunological tests. E coli strains are further distinguished by “H” protein antigens (different types of flagella that make the bacteria motile). Consequently, a particular E. coli strain can be identified as H, followed by a number, and this identifier is added to the “O” name; for example, E. coli 0157:H7. Although this name designation seems complicated, researchers and clinicians use these antigenic identifiers to track specific E. coli strains that cause outbreaks of disease.

One particular E. coli strain, E. coli 0157:H7 is notorious for its potential to cause disease in man; the remainder of this article will focus on this E. coli strain.

What is E. coli 0157:H7?

E coli O157:H7 is a serotype of E. coli bacteria that form the predominant members of one group of EEC. This EEC group is termed enterohemorrhagic E. coli or EHEC. Unfortunately, other terms in the medical literature describe this group (VTEC or Vero toxin-producing E. coli and STEC or Shiga toxin-producing E. coli). Research suggests that only a small number of E. coli 0157:H7 are needed to cause infection (ingestion of about 10–100 organisms) instead of the thousands to millions needed for infections by other E. coli serotypes. Infection is aided by adhesive receptors (pili or fimbriae) that attach the bacteria to human intestinal cells. The most problems caused by the bacteria are due to two Shiga toxins, termed Stx 1 and Stx 2 and also termed Vero toxins. (Toxins are chemicals that are produced by the bacteria and that damage human cell.) These toxins are almost identical to toxins produced by another related bacterium, Shigella spp that can damage and kill intestinal cells and occasionally cause anemia, damage to platelets, and death of cells in other organs, especially the kidneys.

E. coli 0157:H7 is a major health problem. It is estimated to cause infection in more than 70,000 individuals a year in the United States, and the U. S. Centers for Disease Control and Prevention (CDC) suggests E. coli 0157:H7 is responsible for the majority of “E. coli” outbreaks in the U. S. It has been reported to cause both large outbreaks as well as outbreaks in small numbers of individuals.

This diarrheal illness was first recognized when the CDC personnel isolated E. coli O157:H7 from patients in two separate outbreaks in Oregon and Michigan. The illnesses were associated with eating hamburgers at the restaurants of a national chain; some patients experienced hemorrhagic colitis (inflammation and bleeding of the colon). Thus, hemorrhagic colitis due to E. coli 0157:H7 is commonly referred to as hamburger disease. Since that time, E. coli 0157:H7 also has been associated with contaminated water, foods, and unpasteurized or incorrectly pasteurized (heat treated) dairy products.

The most recent outbreak (October/November of 2010) occurred in five states (California, Arizona, Colorado, New Mexico and Nevada). The CDC linked the outbreak to Gouda cheese sold and given away as free samples at Costco stores.

What are the symptoms of E. coli 0157:H7 infections?

Initial symptoms of E. coli O157:H7 infection

The initial symptoms of E. coli O157:H7 infection usually appear about 3 to 5 days (though occasionally in as few as one day or as many as 10 days) after a person ingests the bacteria; the symptoms include

  • nausea,
  • vomiting,
  • stomach cramps, and
  • diarrhea that often is bloody.

The person may have a mild fever of about 100 to 101F (37.7 to 38.3 C). These symptoms can be seen in infected children and adults.

Later symptoms  E. coli O157:H7 infections

The majority of people (especially normal adults) that get the infection resolve the infection without antibiotics in about five to 7 days. However, some people (about 10% of people infected, especially children under the age of 5 and the elderly) develop more severe signs and symptoms, and these people usually require hospitalization and aggressive treatment. These patients develop the usual symptoms listed above, but do not resolve the infection. They develop symptoms that last longer (at least a week) and, if not treated promptly, the infection may lead to disability or death.

These symptoms or complications fall into three main categories;

  • Hemorrhagic (bloody) diarrhea: Hemorrhagic (bloody) diarrhea symptoms are an increased amount of blood in the diarrheal stool that does not seem to resolve and is usually accompanied by severe abdominal pain. Although this may resolve within a week, some individuals can develop anemia and dehydration that can cause death.
  • Hemolytic-uremic syndrome (HUS): Hemolytic-uremic syndrome symptoms of pallor (due to anemia), fever, bruising or nose bleeding (due to destruction of blood platelets that are needed for blood to clot), fatigue, shortness of breath, swelling of the body, especially hands and feet, jaundice, and reduced flow of urine may be seen. HUS symptoms usually develop about 7 to 10 days after the initial diarrhea begins. HUS is the most common cause of kidney failure in children; children under 10 years old are the most likely to develop HUS. E. coli 0157:H7 produces toxins that damage the kidneys and destroys platelets that can lead to kidney failure, excessive bleeding, seizures or death.
  • Thrombotic thrombocytopenic purpura (TTP): Thrombotic thrombocytopenic purpura is caused by the loss of platelets; however, the symptoms that occur are somewhat different and occur mainly in the elderly. The symptoms are fever, weakness, easy, rapid or “spontaneous” bruising, renal failure, and mental impairment that can rapidly progress to organ failures and death. Until the 1980’s, TTP was considered a fatal disease, but since the 1980’s, plasma exchange and infusion techniques have reduced the death rate in TTP patients to about 10%.

How is an infection with E. coli 0157:H7 diagnosed?

The diagnosis of E. coli 0157:H7 infection begins with an accurate history, physical exam, and an analysis of a sample of stool from the patient. A presumptive diagnosis is frequently made if the patient has symptoms of bloody diarrhea and a history of being exposed to persons, foods or liquids known to be a source of an E. coli 0157:H7 outbreak.

Because other disease-causing bacteria (for example, Shigella and Salmonella) can give patients similar initial symptoms, a definite diagnosis is based on culture of E. coli 0157:H7 from the patient’s sample of stool on special culturing plates that then are tested with antiserum (antibodies) that react only with E. coli O157H7. Not all clinics or hospitals have the diagnostic antiserum, so the testing may take a few days.

Because of the high frequency of outbreaks of E. coli 0157:H7, the CDC in 2009 recommended that all patients being screened for community-acquired diarrheal infections have their stool samples analyzed with antisera for Shiga toxins, the toxins that are produced by E. coli 0157:H7 and a few other bacteria, in addition to having cultures of their stool. This approach may result in faster diagnosis of E. coli )157H7 infections.

Blood tests such as a complete blood count (CBC), and blood levels of electrolytes, platelets, blood urea nitrogen (BUN), and creatinine (blood tests that measure function of the kidney) are performed periodically to look for the development of HUS or TTP.

What is the treatment for E. coli 0157:H7?

Patients, especially healthy adults, often require no treatment for E. coli O157:H7 since many infections are self–limited. Moreover, for the acute diarrheal illness, antibiotics have not proven useful. In fact, some studies have shown that antibiotics may increase the chances of developing HUS (up to 17-fold). This effect is thought to occur because the antibiotic damages the bacteria, causing them to release even more toxin. Most investigators suggest antibiotic use only if a patient is septic, that is, there is evidence that the bacterium has spread to parts of the body other than the intestine. In addition, use of atropine and  diphenoxylate (Lomotil), drugs that are commonly used to control diarrhea, may also increase symptoms and trigger complications.

When necessary, treatment includes the replacement of fluids and electrolytes to treat or prevent dehydration. Infection with E. coli 0157:H7 should be treated by a physician especially in children and the elderly. HUS and TTP require complex supportive care (for example, plasma exchange) in the hospital. Patients with kidney failure may need dialysis. Consultation with a critical care specialist is often recommended for the care of patients that develop HUS or TTP.

What are the complications and outcomes of infection with E. coli 0157:H7?

Although these conditions have been presented in the symptoms section, they are presented here again because they are actual complications that can occur after the initial disease begins. Patients without these complications usually have excellent outcomes (prognosis). Individuals who develop the following complications have outcomes that range from good to poor, depending on their overall health and how quickly they are diagnosed, treated, and respond to treatment.

Hemorrhagic diarrhea (hemorrhagic enterocolitis)

The incubation period between exposure to EHEC bacteria, including E. coli O157:H7, and the onset of symptoms is usually 3 to 4 days but may be longer in some individuals. Symptoms of EHEC infection include severe abdominal pain and abdominal tenderness which often is associated with bloody diarrhea. Curiously, there often is little or no fever. The diarrhea typically lasts for 6 to 8 days. Dehydration and blood loss can lead to death in some patients if not corrected early.

Hemolytic-uremic syndrome (HUS)

Hemolytic-uremic syndrome (HUS) is the most worrisome complication of EHEC infection, especially in children, because it is a serious and potentially fatal complication. “Hemolytic” refers to the breakup of red blood cells which leads to anemia. There also is destruction of platelets which leads to low blood levels of platelets (thrombocytopenia), which in turn promotes abnormal bleeding. “Uremic” refers to failure of the kidneys. In addition, problems in the brain with seizures and coma may occur.

Hemolytic-uremic syndrome most commonly affects children under the ages of 10 years and is the most common cause of acute kidney failure in infants and young children. It occurs in about 6% to 10% of hemorrhagic colitis caused by E coli 0157:H7 and usually occurs approximately 7 to 10 days after the onset of diarrhea. Early intervention usually results in better outcomes.

Thrombotic thrombocytopenic purpura (TTP)

Persons infected with E. coli 0157:H7, particularly the elderly, can develop a syndrome similar to HUS called thrombotic thrombocytopenic purpura or TTP with clotting of blood within small blood vessels; anemia due to fragmentation of red blood cells; and a shortage of platelets (thrombocytopenia) that results in easy bruising, neurologic abnormalities, impaired kidney function, and fever. TTP is a serious consequence of E. coli 0157:H7 infection that requires early and aggressive treatment since it results in death in about 10% of all patients who develop it.

How do people get E. coli 0157:H7?

Most commonly, E. coli 0157:H7 comes from eating raw or undercooked ground beef (for example, hamburger) or from drinking raw milk. The bacteria are found in animal feces, particularly cattle feces, and contact with the feces can lead to contamination of many types of food and fluids. In 2010, the FDA recalled several productions of beef, including beef placed in pet food. Less commonly, E. coli O157:H7 can be transmitted from one person to another, usually by direct physical contact..

E. coli 0157:H7 prevention

The CDC recommends the following to prevent infections from E. coli 0157:H7:

  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 or house).
  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 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 touch raw meat.

In addition, many researchers suggest that hamburgers ordered in a restaurant should be cooked through completely, so that no pink hamburger meat is visible inside. This cooking reduces the chance that E. coli will remain alive in the meat. All foods involved in a recall should be put in the trash. No one should attempt to cook the recalled material and eat it.

Because E. coli 0157:H7 is routinely found in the intestines of cattle, companies have developed a vaccine to reduce the number of these bacteria in cattle. The first vaccine for cattle was FDA approved in 2009. There is no vaccine available for E. coli 0157:H7 in humans.

REFERENCES:

CDC.gov. About E. Coli.

CDC.gov. Escherichia coli O157:H7.

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

WHO Global Alert and Response (GAR)

Outbreak of haemolytic uraemic syndrome in Germany

An outbreak of severe illness is causing concern in Germany, where 3 women have died and 276 cases of haemolytic uraemic syndrome (HUS) have been reported since the second week of May. HUS, which can lead to kidney failure, is a complication of an infection by particular Escherichia coli bacteria. While most E.coli bacteria are harmless, a group called enterohaemorrhagic E. coli (EHEC) can produce toxins, known as Shiga toxins or verotoxins, which damage blood cells and the kidneys. EHEC bacteria that produce these toxins are known as Shigatoxin-producing E. coli (STEC) or verocytotoxin-producing E.coli (VTEC), respectively. Many people have been hospitalized, several requiring intensive care, and new cases continue to be identified, the latest having an onset of 25 May. Some other countries have reported cases, notably Sweden, which has reported ten HUS cases, with two in intensive care. All the people affected recently visited Germany, mostly northern Germany.

The outbreak is unusual in that it has developed very rapidly, and an unusually high number of cases affect adults (86% are in people aged 18 years or older), particularly women (67%), instead of the normal high-risk groups, which are young children and the elderly. Nevertheless, cases have also been reported in school-aged children. The unusual E. coli serogroup O104 is suspected of being the pathogen likely to be associated with this outbreak. The epidemiological investigation into the source of the outbreak is under way. Although the source has not yet been determined, cucumbers are under suspicion, and the Robert Koch Institute in Germany is advising people, as a precautionary measure, to avoid eating tomatoes, cucumbers and lettuces, in addition to taking the usual hygiene measures in handling fruit and vegetables.

Germany notified WHO of the outbreak, under the International Health Regulations (IHR), as a potential public health event of international concern, and WHO is sharing information with health authorities in other countries. WHO has also offered technical assistance and stands ready to facilitate collaboration between laboratories to assist countries without the capacity to detect the unusual E. coli serogroup O104. WHO will maintain close contact with the relevant authorities.

EHEC can cause bloody diarrhoea and abdominal pain. People who develop these symptoms who are in or have recently visited Germany, particularly northern Germany, should seek medical advice urgently. The complication of HUS can cause acute kidney failure and can develop after the diarrhoea has resolved. Treatment with anti-diarrhoeal products or antibiotics is not usually recommended, as these may worsen the situation.

Regular hand washing, particularly before food preparation or consumption and after toilet contact, is highly recommended, particularly for people who care for small children or are immunocompromised, as the bacterium can be passed from person to person, as well as through food, water and direct contact with animals.

WHO does not recommend any restrictions in travel to or trade with Germany.

Useful information

Haemolytic uraemic syndrome (HUS) is a life-threatening disease characterized by acute renal failure (uraemia), haemolytic anaemia, and a low platelet count (thrombocytopenia). It predominantly but not exclusively affects children. It results from EHEC infection, and it is estimated that up to 10% of EHEC-affected patients may develop HUS, with a mortality rate ranging up to 5%. Overall, HUS is the most common cause of acute renal failure in young children. It can cause neurological complications (such as seizure, stroke and coma) in 25% of HUS patients and chronic renal sequelae, usually mild, in around 50% of survivors.

Shigatoxin-producing E. coli (STEC) or enterohaemorrhagic E. coli (EHEC) is a severe strain of E. coli bacterium that is commonly found in the gut of animals, mainly ruminants. EHEC produces toxins, known as verotoxins or Shiga-like toxins because of their similarity to the toxins produced by Shigella dysenteriae. They can cause severe foodborne disease. STEC is transmitted to humans primarily through consumption of contaminated foods, such as raw or undercooked ground meat products and raw milk, contaminated water, direct contact with animals or contact with infected people. It is destroyed by thorough cooking of foods until all parts reach a temperature of 70 °C or higher. Symptoms of disease include abdominal cramps and diarrhoea, which may be bloody. Fever and vomiting may also occur. Most patients recover within 10 days, although in a few cases (particularly in young children and the elderly), the infection may lead to a life-threatening disease, such as HUS. Preventive measures for STEC infections are similar to those recommended for other foodborne diseases, including basic good food hygiene practice, as described in the WHO Five keys to safer food.

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