Sources of E. coli infection
E. coli O157:H7 bacteria and other pathogenic E. coli is believed to mostly live in the intestines of cattle (Elder, et al., 2000) but has also been found in the intestines of chickens, deer, sheep, and pigs.
A 2003 study on the prevalence of E. coli O157:H7 in livestock at 29 county and three large state agricultural fairs in the United States found that E. coli O157:H7 could be isolated from 13.8 percent of beef cattle, 5.9 percent of dairy cattle, 3.6 percent of pigs, 5.2 percent of sheep, and 2.8 percent of goats. Over seven percent of pest fly pools also tested positive for E. coli O157:H7 (Keen et al., 2003).
Shiga toxin (Stx)-producing E. coli does not make the animals that carry it ill. The animals are merely the reservoir for the bacteria.
E. coli can be transmitted from several sources:
Foodborne Transmission of Stx-Producing E. coli
E. coli O157:H7 was first recognized as a food borne pathogen in 1982 during an investigation into an outbreak of hemorrhagic colitis (bloody diarrhea) associated with consumption of contaminated hamburgers (Riley, et al., 1983). The following year, Shiga toxin (Stx), produced by the then little-known E. coli O157:H7, was identified as the real culprit.
Outbreaks
- In the ten years following the 1982 outbreak, approximately thirty E. coli O157:H7 outbreaks were recorded in the United States (Griffin & Tauxe, 1991). It is important to note that only about 10 percent of infections occur in outbreaks, the rest are sporadic.
- The actual number is probably much higher because E. coli O157:H7 infections did not become a reportable disease (required to be reported to public health authorities) until 1987 (Keene et al., 1991 p. 60, 73). As a result, only the most geographically concentrated outbreaks would have garnered enough attention to prompt further investigation (Keene et al., 1991 p. 583).
- The CDC has estimated that 83 percent of E. coli O157:H7 infections are foodborne in origin (2009 report). Consumption of any food or beverage that becomes contaminated by animal (especially cattle) manure/feces can result in disease.
Foods that have been identified as sources of contamination include:
- Ground beef
- Venison
- Sausages
- Dried (non-cooked) salami
- Unpasteurized milk and cheese
- Unpasteurized apple juice and cider
- Alfalfa, parsley, and radish sprouts
- Lettuce, cabbage, and spinach
- Fruit nuts and berries
- Cookie dough
The Center for Disease Control (CDC), Enteric Disease Branch, released a report dated September 14, 2009 entitled “Update on the Epidemiology of Shiga toxin-producing E. coli (STEC) in the United States”. The contents of this timely report have been incorporated into this Web piece. CDC’s estimates of the annual number of illnesses caused by Stx-producing E. coli (both O157:H7 and non O157:H7) are as follows:
E. coli O157
- 73,000 illnesses
- 2200 hospitalizations
- 61 deaths
Non-O157 STEC
- 36,700 illnesses
- 1100 hospitalizations
- 30 deaths
E. coli infections continue to largely be a foodborne illness.
For the period of 1998-2007 during which there were 334 outbreaks (7864 illnesses), the vehicles for the infections were as follows:
E. coli O157:H7
- Foodborne: 69%
- Waterborne: 18%
- Animals or their environment: 8%
- Person-to-person: 6%
Non-O157:H7
- Foodborne: 83%
- Waterborne: 9%
- Animals or their environment: 5%
- Person-to-person: 4%
- According to the cited recent CDC report, the mode (kind of food) causing illness secondary to E. coli O157:H7 outbreaks have changed in the past several years. (Note the emergence of leafy vegetables).
E. coli O157:H7
| (1998-2002) |
(2003-2007) |
|
| Beef | 33 |
42 |
| Leafy vegetable | 11 |
41 |
| Dairy | 13 |
13 |
| Fruits-nuts | 41 |
2 |
| Sprouts | 1 |
2 |
| Wild Game | 0 |
1 |
| Poultry | 2 |
0 |
(1990-2007) |
|
| Fruit (nuts, apple juice and cider, berries) | 3 |
| Dairy (cheese, margarine) | 2 |
| Leafy vegetables | 1 |
| Beef | 0 |
The Role of Toxin Receptors
Cattle and other animals are merely reservoirs for E. coli bacteria. Shiga toxin (Stx)-producing E. coli do not make the animals carriers ill because their bodies do not have receptors for the toxin. Receptors are tiny protein structures that are located on the surface of cells, and are specific for a particular antigen (substance), in this case, Shiga toxin. They provide a “docking station” for the toxin, without which it cannot injure animals or their organs (e.g., kidneys).
E. coli in Ground Beef
At one time, prior to the widespread dissemination of E. coli throughout the food chain, hemolytic uremic syndrome (HUS) secondary to E. coli O157:H7 infection was known as “Hamburger Disease”. The ground beef connection has not gone away. Numerous outbreaks and massive recalls of contaminated ground beef continue to plague both the industry and the public.
Meat typically becomes contaminated with E. coli during the slaughtering process, when the contents of an animal’s intestines and feces are allowed to come into contact with the carcass. Unless the carcass is properly sanitized, E. coli bacteria are mixed into the meat as it is ground.
Because E. coli is mixed throughout the meat during the grinding process, and is not just on the surface, ground beef must be cooked throughout to a temperature of 165 degrees Fahrenheit since only thorough cooking will kill them (E. coli prevention).
The fall of 2007 was a dreadful season. The Food Safety and Inspection Service (FSIS) of the US Department of Agriculture (USDA) announced the recall of nearly 30 million pounds of ground beef in 20 separate recalls for E. coli contamination in 2007. Many of the recalls were announced after illness had been traced to the specific contaminated products.
One of Several September 2007 Ground Beef E. coli Outbreaks
On September 29, 2007, the USDA and FSIS announced that 21.7 million pounds of frozen ground beef patties were being recalled for possible E. coli O157:H7 contamination.
The announcement came after health officials in several states, who were investigating reports of E. coli O157 illnesses, found that many ill persons had consumed the same brand of frozen ground beef patties.
State public health departments and federal laboratories tested patties recovered from patients’ homes; tests were conducted by the New York State Wadsworth Center Laboratory and by a FSIS laboratory on opened and unopened packages of the same brand of frozen ground beef patties. They yielded E. coli O157 isolates with several different “DNA fingerprint” patterns, as determined through Pulsed Field Gel Electrophoresis (PFGE).
An October 9, 2007 CDC news release stated that “several state health departments, CDC, and the USDA-FSIS were investigating a multi-state outbreak of Escherichia coli O157:H7 infections” (CDC, October 9, 2007).
Investigators compared the “DNA fingerprint” patterns of E. coli isolated from 35 ill individuals to E. coli strains isolated from the recalled ground beef patties and found that the strain isolated from the ill people matched at least one of the DNA patterns of E. coli strains found in the frozen ground beef patties.
Three cases had confirmed associations with recalled products because the E. coli strain isolated from their stool was also isolated from meat in their home.
The ill persons, ages one to 77 years, resided in eight states: Connecticut (2), Florida (1), Indiana (1), Maine (1), New Jersey (8), New York (11), Ohio (1), and Pennsylvania (10).
E. coli in Fresh Fruits and Vegetables
Fruit that comes in contact with animal, especially cattle, feces, (as might happen if fruit has fallen and is harvested/picked from/off the ground), can also transmit Stx-producing E. coli.
A specific example is the November 1996 unpasteurized apple juice outbreak:
- On November 1, 1996, Odwalla Company recalled all of its products containing unpasteurized apple juice after several children developed Hemolytic Uremic Syndrome (HUS) Add link to about-hus.com.
- The public health agencies that conducted an investigation into the Odwalla apple juice E. coli outbreak concluded that contamination occurred when “dropped” apples were harvested from ground that had been contaminated by cow manure; it is important to know that E. coli O157:H7 can survive for long periods of time (e.g., > 1 yr [in compost], for example).
- This tragedy led to the dramatic implementation of juice pasteurization
Fresh vegetables can become contaminated pre- or post-harvest. Contaminated seeds, irrigation water, and flooding have contributed to E. coli outbreaks traced to sprouts, lettuce, spinach, parsley, and other fresh produce. According to the September 2009 CDC report, there were no leafy green vegetables implicated in any E coli O157:H7 outbreaks prior to 1995, but since then (1995-2005) there have been 27 such outbreaks:
- Lettuce and lettuce salads: 21 outbreaks
- Cabbage: 3 outbreaks
- Parsley: 2 outbreaks
- Spinach: 1 outbreak
June 2006 Lettuce E. coli Outbreak
In early August 2006, public health officials in a mid-sized city in Utah became aware that several people attending a teachers’ conference had contracted E. coli O121:H19 (another Shiga toxin-producing E. coli). The Weber-Morgan Health Department (HD) issued a news release indicating that three people had contracted E. coli O121:H19 from the same source, and that two had developed HUS. Several days later, HD officials revised the number of outbreak victims to four, including three who had developed HUS (Weber-Morgan Health Department, 2006, August 7).
One of the patients with confirmed HUS had not attended the teachers’ conference, but had eaten cheeseburgers with iceberg lettuce prepared at the same restaurant during the outbreak. The second confirmed HUS case was an attendee of the teachers’ conference. A third was determined to be a secondary case who acquired E. coli from a person infected at the conference. Samples from three of the HUS patients with E. coli O121:H19 were laboratory-confirmed as genetic matches through DNA sub-typing using Pulsed Field Gel Electrophoresis (PFGE), confirming that their E. coli infections all came from the same source.
Eventually, HD officials concluded that the source of the E. coli outbreak was iceberg lettuce prepared at the same fast-food facility. By the end of the outbreak at least 69 people became ill.
Spinach E. coli Outbreak, August and September 2006
On Friday, September 8, 2006, Wisconsin Department of Health (WDOH) epidemiologists alerted officials at the Centers for Disease Control and Prevention (CDC) that a small cluster of E. coli O157:H7 infections with an unknown source had been identified. Separately, the State of Oregon Public Health Division (ODPH) also noted a small cluster of E. coli infections that same day. Both WDOH and ODPH uploaded the PFGE patterns, (genetic fingerprints), of the E. coli O157:H7 strains that had been isolated from victims from their respective states to PulseNet—an epidemiology tool that serves as an early warning system for outbreaks of foodborne illness that is comprised of a national network of public health laboratories that performs DNA “fingerprinting” on bacteria that may be foodborne. PulseNet identifies and labels each “fingerprint” pattern and permits rapid comparison of these patterns through an electronic database at the CDC to identify related strains. Through PulseNet, CDC became aware that the Wisconsin and Oregon outbreaks had been caused by an indistinguishable strain of E. coli, suggesting a common source.
On September 13, 2006, Wisconsin and Oregon health officials reported to CDC that interviews of ill individuals suggested the consumption of fresh-bagged spinach was common in both clusters, and on September 14, 2006, the Food and Drug Administration (FDA) warned the public not to eat fresh-bagged spinach. By September 15, CDC had received nearly 100 reports of E. coli infection among residents of several states.
The epidemiologic investigation into the outbreak indicated that the outbreak source was bagged spinach produced in a single plant, on a single day, during a single shift. Between August 1 and October 6, 2006, public health officials identified 199 individuals infected with the outbreak strain of E. coli O157:H7 in 26 states; 102 were hospitalized, 31 developed HUS, and 5 died.
Lettuce E. coli Outbreak, November 2006
On Jan 12, 2007, the Food and Drug Administration (FDA) announced that it had moved closer to identifying the source of an E. coli O157:H7 outbreak that had resulted in the approximately 81 illnesses in November and December of 2006. Cases were reported in Minnesota (33), Iowa (47), and Wisconsin (1). Twenty-six people were hospitalized, and two developed HUS. The investigation into the outbreak revealed that all ill individuals had contracted E. coli after eating foods at chain Mexican food restaurants in Iowa and Minnesota. Epidemiologic studies by Minnesota and Iowa health officials identified shredded iceberg lettuce served in the restaurants as the likely source of the outbreak. Minnesota, Iowa, and Wisconsin health officials worked with public health agencies in California in a trace-back effort to determine where the E. coli-contaminated lettuce originated. During the trace-back investigation the strain of E. coli O157:H7 associated with the outbreak was found in two environmental samples gathered from dairy farms near a lettuce field in California’s Central Valley. The FDA was then able to locate the site where the lettuce was grown by reviewing records obtained from the lettuce processor.
Cookie Dough E. coli outbreak, 2009
On June 18, 2009, the Colorado Department of Public Health and Environment (CDPHE) issued a press release stating that CDPHE, the Centers for Disease Control and Prevention (CDC), and other state health departments were investigating an outbreak of E. coli O157:H7 infections in persons who had eaten raw pre-packaged, refrigerated cookie dough. A joint investigation by state public health agencies, the CDC, and U.S. Food and Drug Administration resulted in the conclusion that at least 80 people in 30 states had become ill with E. coli O157:H7 infections after eating the contaminated cookie dough; 10 cases progressed to HUS.
Waterborne Transmission of Stx-producing E. coli
Water intended for recreation (e.g., pools, shallow lakes) and for human consumption can also become contaminated. When lakes become contaminated, several weeks or months can be required for water quality conditions to improve or return to normal.
1998 E. coli outbreak at a water park
In 1998, an E. coli outbreak occurred among children who had visited a water theme park in the Southeast. Health officials traced the outbreak to an infected toddler who played in a pool while wearing diapers. Even though the pool was chlorinated, its concentration and contact time was presumably insufficient to kill the E. coli resulting from fecal contamination by the toddler, and other children who were in the pool ingested E. coli bacteria while playing in the pool.
1998 E. coli outbreak associated with a municipal water system
Also in 1998, the municipal water system in Alpine, Wyoming, became contaminated with E. coli, resulting in 157 illnesses, with four people developing HUS. The outbreak investigation revealed that the town’s water supply, which came from an unchlorinated underground spring, became contaminated with surface water prior to the outbreak. A large pool of water was found in the area over the water collection pipes, probably the result of a late snow melt combined with heavy rains and ground water outfalls. In addition, investigators found numerous deer and elk feces were present in the pool area, as animals came to the pool to drink (Olsen, et al., 2002).
1999 E. coli outbreak associated with exposure to recreational water
E. coli contamination at a lake in Connecticut led to an E. coli outbreak in 1999. Eleven people became ill with E. coli infections, and 3 children developed HUS; the attack rate was highest among those who were younger than 10 years who swam and/or swallowed water while swimming (McCarthy, et al., 2001; Tara, et al., 2001).
1999 E. coli outbreak associated with well water
Also in 1999, the New York State Department of Health investigated what is believed to be the largest outbreak of waterborne E. coli O157:H7 illness in United States history. The outbreak occurred at a fair in Washington County, New York, in August of 1999 (New York State Department of Health and Novello, 2000, March). A total of 781 persons were identified with suspected infections of E. coli O157:H7 and/or Campylobacter jejuni. Of these cases 127 persons were culture-confirmed to be ill with E. coli O157:H7, 71 individuals were hospitalized, 14 persons exhibited HUS, and 2 people died.
The environmental and site investigation indicated that unchlorinated water from a well serving the southwestern portion of the fairgrounds was contaminated with E. coli O157:H7 (DOH News, 1999, September 16). Samples of manure collected from a barn located 50 feet from the well and samples from the groundwater flow from the manure storage area located 80 feet from the well tested negative for E. coli O157:H7. However, samples from the septic system tested positive for E. coli O157:H7.
Consumption of only two food or beverage items, soda with ice or ice in any drink, was reported by a majority of the culture-confirmed case patients. MMWR Weekly (1999) reported that the pulsed-field gel electrophoresis testing by the New York state laboratory indicated that the DNA fingerprints of E. coli O157:H7 isolates from the well, the water distribution system, and most confirmed cases were similar.
The epidemiological investigation of this outbreak concluded that a significant relationship was associated with the incidence of the outbreak and the consumption of beverages purchased from vendors supplied with water from the unchlorinated well.
Animal-to-Person Transmission of E. coli
Animal-to-person spread of E. coli also occurs, and has been identified in several outbreak-situations as well as in isolated settings, such as homes.
E. coli at Fairs and Petting Zoos
The mode of transmission for E. coli at agricultural fairs, petting zoos, and farm visits was previously thought to be limited to hand-to-mouth transmission following contact with contaminated surfaces or animals; however, recent indications are that inhalation of dust particles could potentially cause E. coli infection. See www.fair-safety.com
Person-to-Person transmission of E. coli
Outbreaks of E. coli O157:H7 can also be caused by person-to-person transmission, which has occurred in daycare centers, hospitals, nursing homes, and private residences. Because the infectious dose is so small it is very easy for the bacteria to be transmitted among people with close physical contact.
2000 E. coli outbreak associated with a daycare
In August of 2000, a daycare in California was identified as the source of an E. coli O157:H7 outbreak. Health department officials who investigated the outbreak determined that the probable “index case”—a child who unknowingly brought the bacteria into the facility—experienced “explosive diarrhea at the daycare on the afternoon of 8-3-00.”
Shortly thereafter, four other children became infected with E. coli O157:H7 on successive days, the 6th, 7th, 8th and 9th of August, 2000. All of the children were in the same day care group. In addition to the illnesses of the children, the mother of one child, and another child’s sibling became ill and tested positive for E. coli. Another toddler also became ill.
According to the Facility Evaluation Report by the Department of Social Services, “[t]he cause of the [E. coli O157:H7] outbreak was due to a sponge being used simultaneously for wiping down a changing table and wiping down a table used for serving meals.”
E. coli case associated with person-to-person contact
A toddler in Idaho who had mild non-bloody diarrhea routinely shared the family’s bathtub with a neighbor’s child. Several days after the two children bathed together, the neighbor child developed bloody diarrhea that progressed to severe HUS. A few days later, the first toddler was also admitted to the same children’s hospital with HUS. Tragically, the neighbor’s child died.
E. coli case associated with person-to-person contact
A father who worked on a dairy farm contracted mild, non-bloody E. coli diarrhea that was transmitted to his son, who developed HUS. The same event reoccurred two years later. The son’s second episode was devastating. Although the son survived, he was left with blindness and severe brain damage.