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E. coli O157:H7 A Potential Health Concern 1
H. Petridis, G. Kidder, and A. Ogram2Purpose
The purpose of this fact sheet is to inform the public about important aspects of the exposure of humans to E. coli O157:H7, an emerging pathogen. This feces-transmitted microorganism has been causing illness since 1982 and its increased occurrence worldwide has become a public concern. In this fact sheet we will discuss briefly the organism's health impact, how people can be infected, the modes of dissemination, associated risk factors, and measures for preventing the infection.E. coli and E. coli O157:H7
Escherichia coli are bacteria that normally inhabit the intestines of humans and animals. Most strains are known to be harmless, but several of them can cause mild to serious disease. One strain in particular, named O157:H7, can cause severe diarrhea and in some cases lead to serious complications, even death. O157:H7 is known to be present in the gastrointestinal tract of cattle, mainly dairy calves.Three unique characteristics of O157:H7 that distinguish it from other E. coli strains are:
- Its dangerous health implications: infection can lead to renal (kidney) damage and can be fata.
- Its unusual persistence in the environment: O157:H7 survives at low temperatures and under acidic conditions.
- Its very small infective dose: a few bacteria, from 10 to 100 cells, are sufficient to cause disease (Table 1 ).
Outbreaks
E. coli O157:H7 has been detected throughout the world, but most outbreaks have been documented in Canada, United Kingdom, and USA. The largest outbreak occurred in Japan in 1996 ( Table 2 ). Despite improved reporting of E. coli O157:H7 outbreaks, its incidence may still be underestimated because:
- Clinical laboratories do not routinely culture stools specifically for E. coli O157:H7.
- E. coli O157:H7 is more likely detected if stools are cultured within the first four days of infection.
Infection
Who is at risk of infection?
People from any age group are susceptible to infection with E. coli O157:H7. However, children, the elderly, and immuno-compromised individuals are more likely to get infected and develop complications. Residents of rural areas and workers employed at farms and slaughterhouses have greater exposure to E. coli O157:H7 due to possible contact with animal manure. However, large outbreaks have occurred in day care centers and nursing homes, posing risk to people associated with such settings. Consumers of bovine products may also be at a higher risk since most outbreaks reported involved consumption of improperly cooked ground beef.What are the symptoms and complications?
Illness starts with severe diarrhea and abdominal cramps, often developing into bloody diarrhea. The symptoms usually occur three to four days after exposure. Some people infected by E. coli O157:H7 have no symptoms at all or only mild diarrhea. Complications include the hemolytic uremic syndrome (HUS) which results in destruction of red blood cells and kidney failure. HUS can also affect the nervous system causing seizures and eventually coma. High numbers of white blood cells, fever, anemia, and renal insufficiency are signs for HUS development. Although most people recover from HUS, it can be fatal.What kind of treatment?
As with any form of diarrhea, intake of plenty of fluids is recommended. Symptoms generally disappear within five to ten days without any specific treatment. However, if bloody diarrhea develops, immediate medical assistance should be sought. Close observation should be carried out for the development of complications that might require immediate hospitalization and therapy (e.g., kidney dialysis). Antibiotics are not recommended.Risk Factors
A person becomes infected by ingesting the O157:H7 bacteria. The most common means by which this happens is through food that has come in contact with contaminated feces. Undercooked ground beef contaminated during the slaughtering process is a known cause of many outbreaks as noted in Table 2 . E. coli O157:H7 has also been found in other animals such as sheep, pigs, goats, poultry, and deer. Wild and domestic animals that live around cattle farms may also harbor this species. Therefore, animals other than cattle may also be sources of E. coli O157:H7 infection. Other risk factors include drinking or swimming in contaminated water, handling animal feces, and eating fruit and vegetables fertilized or irrigated with animal manure. Poor personal hygiene (e.g., not washing hands properly after using the toilet) and unsafe food preparation practices also increase the risk of spreading O157:H7 infection.Potential Sources of Infection
See Table 3 and Figure 1 .
Figure 1. Sources of E. coli infection. Prevention and Recommendations
In the home
- Cook ground beef until the meat is brown and juices run clear.
- Drink only milk, milk products and fruit juices that have been pasteurized.
- Wash fruit and vegetables adequately.
- Wash hands with soap after using the toilet.
- Take special care when handling and disposing of diarrhea-contaminated diapers.
- Wash hands before food preparation.
- Wash kitchen utensils and surfaces after handling raw meat to avoid cross-contamination.
- Make sure the drinking water has been properly treated.
On the farm
- Use potable quality water for washing fruit and vegetables.
- Manage fecal waste so as not to contaminate water supplies.
- Avoid spreading fecal material off-farm via clothes and shoes, tools, etc.
- Wash hands with soap after petting or handling animals.
In meat processing facilities
- Assure good hygienic practices in slaughterhouses and processing units.
- Apply approved treatments of carcasses to remove fecal bacteria.
Summary
E. coli O157:H7 is a unique and harmful strain of bacteria which can cause serious health problems in infected persons. It is found mainly in the feces of some cattle, and it appears to be widespread in the environment. It may be transmitted to humans when meat contaminated with feces during slaughter is consumed without proper cooking. It is also easily spread among children through unsanitary practices when a child has O157:H7-caused diarrhea.Prevention of infection as well as dissemination of hemorrhagic colitis disease is easily accomplished by ordinary habits such as washing hands, cooking ground meat thoroughly, and paying particular attention to hygiene around persons with diarrhea.
Recapping about hemorrhagic colitis disease:
- Causative agent: E. coli O157:H7.
- Principal known reservoir: Dairy cattle.
- Occurrence: Worldwide, but most often reported in USA, Canada, UK.
- Sources of infection: Undercooked contaminated ground beef; contaminated recreational and drinking water; poorly washed contaminated fruit and vegetables; infected humans.
- Mode of transmission: Food-to-human, water-to-human, human-to-human, and animal-to-human.
- Preventive measures: Good hygienic and sanitary practices.
Further information
- Escherichia coli O157:H7 in humans and cattle. 1997. USDA:APHIS:VS Center for Epidemiology and Animal Health. 555 South Howes, Fort Collins, CO 80521.
- E. coli information. http://www.cdc.gov/ncidod/dbmd/diseaseinfo/escherichiacoli_g.htm
- Preventing foodborne illness: Escherichia coli O157:H7. http://www.ifst.org/hottop1.htm
Tables
Table 1. Estimated infectious dose of bacteria species associated with diarrhea.
Bacteria Species Estimated infectious dose (bacteria cell number) Disease
Common source
E. coli O157:H7
10 to 100 Hemorrhagic colitis undercooked ground beef E. coli 1,000,000 to 100,000,000 Traveler's diarrhea poor hygienic standards Salmonella 100 to 1,000,000,000 Salmonellosis undercooked poultry and raw eggs Shigella spp. 10 to 1,000,000 Dysenteria poor personal hygiene Vibrio cholerae 1,000,000 to 1,000,000,000 Cholera raw or undercooked seafood, contaminated water Principal source: Foodborne Pathogens: Risks and Consequences, Report No. 122, CAST- Council for Agricultural Science and Technology, September 1994.
Table 2. Largest E. coli O157:H7 outbreaks.
Year
Place No. of people sick Contamination source
1989
Montana, USA 243
Undercooked ground beef 1996
Sakai, Japan 5,727
Poorly washed white radish sprouts 1996
Scotland, UK 496
Undercooked ground beef 2000
Walkerton, Canada >2,000
Contaminated drinking water 2002
Pennsylvania, USA 51
Petting infected dairy animals Table 3. Potential Sources of Infection.
Undercooked ground meat =>
meat comes in contact with cattle feces at slaughter Poorly washed fresh fruit and vegetables =>
fruit and vegetables grown in manured soil or irrigated with contaminated manure slurry Raw milk =>
milk comes in contact with contaminated cattle feces Drinking water =>
water supplies contaminated with animal wastes and inadequately treated Recreational water =>
stream or lake contaminated with animal or human waste Manure handling =>
direct contact with contaminated animal feces Handling livestock =>
direct contact with infected animals Person-to-person contact =>
person who does not wash hands after using toilets or after changing diapers, including especially day care centers and nursing homes
Footnotes
1. This document is SL-146, one of a series of fact sheets of the Soil and Water Science Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. First Published August 1998. Revised October 2002. Please visit the EDIS Web site at http://edis.ifas.ufl.edu.2. H. Petridis, former graduate student, G. Kidder, emeritus professor, and A. Ogram, associate professor, Soil and Water Science Department, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611.
The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.
U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.
Copyright Information
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