E. coli Facts
Escherichia coli (abbreviated as E. coli) are a very large and diverse group of bacteria that live in the intestinal tracts of warm blooded animals (predominantly cattle, pigs, goats, sheep, deer, and elk) and humans. The E. coli bacteria do not affect the animals - the animals are merely a carrier for the bacteria.
There are over 700 serotypes of E. coli. The most virulent of these produce shiga toxins and are called “shiga toxin-producing” E. coli, or STEC for short. They are sometimes referred to as verocytotoxic E. coli (VTEC) or enterohemorrhagic E. coli (EHEC). Shiga toxins are so named because they are virtually identical to those produced by another well known bacteria, i.e. shigella dysenteriae.
The most commonly identified STEC in North America is E. coli O157:H7 (often shortened to E. coli O157 or even just “O157”). When you hear news reports about outbreaks of “E. coli” infections, they are usually referring to E. coli O157.
In addition to E. coli O157, many other kinds (called serogroups) of STEC cause hemorrhagic colitis (bloody diarrhea). These other kinds are sometimes called “non-O157 STEC.” E. coli serogroups O26, O111, and O103 are the non-O157 serogroups that most often cause illness in people in the United States. The non-O157 STEC are not nearly as well understood, partly because current protocols do not test for them and thus outbreaks due to them are rarely identified. As a whole, the non-O157 serogroup is less likely to cause severe illness than E. coli O157; however, some non-O157 STEC serogroups can cause the most severe manifestations.
STEC organisms are extremely virile - they can survive for weeks on surfaces such as kitchen counters and food preparation surfaces, and over a year within other materials. Unfortunately, a very small amount of E. coli in one’s system can be deadly - the infectious dose of E. coli has been reported to be as few as 10 organisms.
E. coli O157:H7
The Center for Disease Control (CDC) first discovered E coli O157:H7 in 1975, although the bacteria was not implicated in food-borne illnesses until 1982 during an investigation into an outbreak of hemorrhagic colitis associated with contaminated hamburger.
Since 1982, more than 100 E. coli O157:H7 outbreaks have been detected in the United States. In actuality, that number is probably much higher because E. coli O157:H7 did not become a reportable disease (one that, upon detection by a lab, doctor, or hospital - must be reported by law to local health officials ) until 1987.
The CDC estimates that every year over 73,000 are sickened, 2000 are hospitalized, and 60 die as a result of E. coli O157:H7 poisoning.
How is E. Coli transmitted?
The vast majority (reported 85%) of all E. coli illnesses are foodborne related. Inevitably, infections start when you swallow STEC—in other words, when you get tiny (usually invisible) amounts of human or animal feces in your mouth. Unfortunately, this happens more often than we would like to think about.
Although most E. coli illnesses are foodborne related, a small percentage have been tied to other transmission vehicles such as water, animals, ads person-to-person contact. People have become infected by swallowing lake water while swimming, touching the environment in petting zoos and other animal exhibits, and by eating food prepared by people who did not wash their hands well after using the toilet. Some examples are outlined below.
1. Foodborne transmission
The majority of foodborne STEC outbreaks in the past 25 years were related to the consumption of ground beef. Several recent outbreaks, however, have been linked to spinach, lettuce, sprouts, parsley, raw milk, yogurt, and unpasteurized apple juice.
Between August 1 and October 6, 2006, public health officials identified 199 individuals infected with an identical strain of E. coli O157:H7. Of those individuals, 102 were hospitalized, and 31 developed HUS, and 3 died. An epidemiological investigation revealed that the consumption of fresh bagged spinach was strongly associated with illness. E. coli O157:H7 was isolated from 13 packages of spinach supplied by patients living in 10 states. Eleven of the packages had lot codes reflecting a common manufacturing date at a single manufacturing facility. Two packages did not have lot codes available but had the same brand name as the other packages. The “DNA fingerprints” of all of the samples matched that of the outbreak strain.
In November and December of 2006, public health officials identified 71 individuals in 5 states infected with an identical strain of E. coli O157:H7. Of those individuals, 53 were hospitalized, and 8 developed HUS. An epidemiological investigation revealed that the consumption of lettuce, cheese, and ground beef at the Taco Bell restaurant chain was strongly associated with illness.
Between July 5 and September 24, 2007, public health officials identified 40 individuals infected with an identical strain of E. coli O157:H7. Of those individuals, 21 were hospitalized, and 2 developed HUS. Health officials in several states who were investigating reports of E. coli O157 illnesses found that many ill persons had consumed Topp’s brand frozen ground beef patties. Opened and unopened packages of Topp’s brand frozen ground beef patties collected from patients’ homes yielded E. coli O157 isolates with several different PFGE patterns. Investigators compared the PFGE patterns from ill persons and meat samples and found 40 patients PFGE patterns matching at least one of E. coli strains found in Topp’s brand frozen ground beef patties.
2. Water borne transmission
Several incidents have shown that both drinking water and recreational water (swimming pools, lakes) can serve as transmission vehicles for E. coli bacteria.
The first reported waterborne E. coli outbreak occurred in Missouri in 1989. Portland, Oregon in 1991. More than 240 people were infected, 32 were hospitalized, and 4 died. Backflow from a broken water main was thought to be the source of contamination.
Another waterborne E. coli outbreak occurred in Portland, Oregon in 1991. Of the 59 people infected, 21 contracted E. coli O157:H7. An epidemiological investigation revealed that those infected had swum in a local lake in the 3 weeks preceding their illness. Transmission was thought to have occurred when the swimmers accidentally swallowed lake water that had become fecally contaminated by other bathers.
In the summer of 1998, a large outbreak of E. coli O157:H7 infections occurred in Alpine, Wyoming. Over 150 people were sickened, including citizens of alpine and persons from14 other states. Four people contracted HUS, and no one died. Illness was strongly associated with drinking unchlorinated water from the Alpine municipal water system.
In September 1999, a large waterborne outbreak of E. coli O157:H7 infections occurred at a fair in Washington County, New York. Epidemiological investigation revealed that the likely source was unchlorinated drinking water from a well serving a portion of the fairgrounds. The water was likely contaminated when cow manure seeped into a well after a rainstorm. Of the 781 people infected, 71 were hospitalized, 14 contracted HUS, and 2 died.
It has been reported that small water systems (those that serve fewer than 3,300 people) , collectively serve approximately 15% of the United States population. These systems may be less likely to be adequately chlorinated and to routinely monitor for contaminants. The outbreaks listed above confirm the potential of these small, unprotected and unchlorinated water systems to be an important source of infection with E. coli O157:H7.
3. Animal to person transmission
The transmission of E. coli from animals to persons has been well documented. Several outbreaks have originated in petting zoos, county fairs, and on farms, as shown below.
In October 2004, a large outbreak of E. coli O157:H7 occurred in North Carolina. Of the 108 infected, 20 were hospitalized, and15 contracted HUS. Visits to a petting zoo at the state fair was associated with illness. Environmental samples from the petting zoo yielded E coli O157:H7, with indistinguishable PFGE patterns from the stoll samples of infected persons. Persons were found to have become infected after contact with manure and engaging in hand-to-mouth behaviors with sheep and goats in the petting zoo.
In March 2005, Florida health officials identified a cluster of 22 E. coli O157:H7 infections, including seven HUS cases, related to attendance at Florida Fairs and Festivals during February 10–21, 2005, and March 3–13, 2005. Early patient interviews identified no common food or water exposure but did implicate a common animal exposure (i.e., petting zoo attendance). Three implicated fairs had one common animal vendor - an exhibitor of a farm animal petting zoo. Stool samples from infected persons were sent to the Florida Department of Health for culture and PFGE typing of E. coli O157:H7 isolates. Stool samples were also collected the environment and from 36 animals exhibited at the petting zoos. The human, environmental, and animal samples yielded E. coli O157:H7 isolates with an identical PFGE pattern and the petting zoo was determined to be the source of the outbreak. Of the 73 illnesses, 12 developed HUS.
In July 2005, two children hospitalized with E. coli O157:H7 infection were reported to the Arizona Department of Health Services. Isolates from the two children had indistinguishable PFGE patterns. Both children had visited a petting zoo in Arizona. One child had direct contact with petting zoo animals; the second child only had possible contact with exterior railings at the petting zoo. Both children had played in an area immediately adjacent to and downhill from the petting zoo facility. Fecal specimens from petting zoo animals yielded 12 E. coli O157:H7 isolates with PFGE patterns indistinguishable from those taken from the children. Upon notification of the results, zoo officials immediately closed the petting zoo and adjacent play area.
4. Person to person transmission
E. coli can also be transmitted by person to person contact, which frequently occurs in daycare centers, hospitals, and nursing homes. Hand washing and strict cleaning guidelines thus become an important issue in preventing such transmissions.
In February 2009, 21 children and a caregiver contracted E. coli in Chicago, Illinois. Three were hospitalized and released. The Cook County Health Department attributed the outbreak to inadequate hand-washing.
In August 2000, a daycare facility in Folsom, California was linked to an E. coli O157:H7 outbreak that sickened 5 students. In addition to the students, one parent and a sibling also contracted and tested positive for E. coli O157:H7. The source of the outbreak was a sponge used to wipe down both the changing table and serving table.
Who gets STEC infections?
People of any age can become infected. Very young children and the elderly are more likely to develop severe illness and hemolytic uremic syndrome (HUS) than others, but even healthy older children and young adults can become seriously ill.
What are the symptoms of STEC infections?
E. coli has emerged in recent years as the predominant cause of hemmorrhagic colitis. This illness, with the characteristic symptoms of abdominal cramps and bloody diarrhea, can progress into a severe, life-threatening complication known as hemplytic uremic syndrome.
The symptoms of STEC infections vary for each person but often include severe stomach cramps, diarrhea (often bloody), and vomiting. If there is fever, it usually is not very high (less than 101˚F/less than 38.5˚C). Most people get better within 5–7 days. Some infections are very mild, but others are severe or even life-threatening.
What are the complications of STEC infections?
Around 5–10% of those who are diagnosed with STEC infection develop a potentially life-threatening complication known as hemolytic uremic syndrome (HUS). Clues that a person is developing HUS include decreased frequency of urination, feeling very tired, and losing pink color in cheeks and inside the lower eyelids. Persons with HUS should be hospitalized because their kidneys may stop working and they may develop other serious problems. Most persons with HUS recover within a few weeks, but some suffer permanent damage or die.
How soon do symptoms appear after exposure?
The time between ingesting the STEC bacteria and feeling sick is called the “incubation period.” The incubation period is usually 3-4 days after the exposure, but may be as short as 1 day or as long as 10 days. The symptoms often begin slowly with mild belly pain or non-bloody diarrhea that worsens over several days. HUS, if it occurs, develops an average 7 days after the first symptoms, when the diarrhea is improving.
Timeline for Reporting of E Coli cases
To find cases in an outbreak of E. coli O157 infections, public health laboratories perform a kind of “DNA fingerprinting” on E. coli O157 laboratory samples. Investigators determine whether the “DNA fingerprint” pattern of E. coli O157 bacteria from one patient is the same as that from other patients in the outbreak and from the contaminated food. Bacteria with the same “DNA fingerprint” are likely to come from the same source. Public health officials conduct intensive investigations, including interviews with ill people, to determine if people whose infecting bacteria match by “DNA fingerprinting” are part of a common source outbreak.
A series of events occurs between the time a patient is infected and the time public health officials can determine that the patient is part of an outbreak. This means that there will be a delay between the start of illness and confirmation that a patient is part of an outbreak. Public health officials work hard to speed up the process as much as possible. The timeline is as follows:
Incubation time: The time from eating the contaminated food to the beginning of symptoms. For E. coli O157, this is typically 3-4 days.
Time to treatment: The time from the first symptom until the person seeks medical care, when a diarrhea sample is collected for laboratory testing. This time lag may be 1-5 days.
Time to diagnosis: The time from when a person gives a sample to when E. coli O157 is obtained from it in a laboratory. This may be 1-3 days from the time the sample is received in the laboratory.
Sample shipping time: The time required to ship the E. coli O157 bacteria from the laboratory to the state public health authorities that will perform “DNA fingerprinting”. This may take 0-7 days depending on transportation arrangements within a state and the distance between the clinical laboratory and public health department.
Time to “DNA fingerprinting”: The time required for the state public health authorities to perform “DNA fingerprinting” on the E. coli O157 and compare it with the outbreak pattern. Ideally this can be accomplished in 1 day. However, many public health laboratories have limited staff and space, and experience multiple emergencies at the same time. Thus, the process may take 1-4 days.
The time from the beginning of the patient’s illness to the confirmation that he or she was part of an outbreak is typically about 2-3 weeks. Case counts in the midst of an outbreak investigation must be interpreted within this context.
How common are STEC infections?
Experts think that there may be about 70,000 infections with E. coli O157 each year in the United States. We can only estimate because we know that many infected people do not seek medical care, many do not submit a stool specimen for testing, and many labs do not test for STEC. We think that a similar number of persons have diarrhea caused by non-O157 STEC. Many labs do not identify non-O157 STEC infection because it takes even more work than identifying E. coli O157.
How are STEC infections diagnosed?
STEC infections are usually diagnosed through lab testing of stool specimens (feces). Identifying the specific strain of STEC involved is very important for public health purposes, such as finding outbreaks. Most labs can determine if an STEC is present and can identify E. coli O157. To determine the O group of non-O157 STEC, strains must be sent to a State Public Health laboratory.
How long can an infected person carry STEC?
STEC typically disappear from the feces by the time the illiness is resolved, but may be shed for several weeks, even after symptoms go away. Young children tend to carry STEC longer than adults. A few people keep shedding these bacteria for several months. Good hand-washing is always a smart idea to protect yourself, your family, and other persons.
What is the best treatment for STEC infection?
Non-specific supportive therapy, including hydration, is important. Antibiotics should not be used to treat this infection. There is no evidence that treatment with antibiotics is helpful, and taking antibiotics may increase the risk of HUS. Antidiarrheal agents like Imodium® may also increase that risk.
Should an infected person be excluded from school or work?
School and work exclusion policies differ by local jurisdiction. Check with your local or state health department to learn more about the laws where you live. In any case, good hand-washing after changing diapers, after using the toilet, and before preparing food is essential to prevent the spread of these and many other infections.
How can STEC infections be prevented?
1. WASH YOUR HANDS thoroughly after using the bathroom or changing diapers and before preparing or eating food.
2. WASH YOUR HANDS after contact with animals or their environments (at farms, petting zoos, fairs, even your own backyard)
3. 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.”
4. AVOID raw milk, unpasteurized dairy products, and unpasteurized juices (like fresh apple cider).
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.
