There were major technological improvements in the laboratory, which involved DNA fingerprinting of E.coli O157:H7 isolates. The method is to take DNA from bacteria of a known type, apply certain enzymes to "chop up" the DNA, and separate the components of varying molecular weights on a gel. This allows epidemiologists to use these different subgroups as markers when an outbreak occurs. In this way we can match cases and more readily pinpoint the source of the contamination.
For Washington State, we have the luxury of two methods: microrestriction fingerprinting, performed by Mansour Samadpour's laboratory at the University of Washington, and pulsed field gel electrophoresis (PFGE) at the Washington State Public Health Laboratory. We have chosen to use PFGE because it is a standardized and published method performed at the CDC and several state health departments. Currently, the protocol used at all these sites
is a one day procedure developed by Romesh Gautom of the Washington State Public Health Laboratory (7).
Third, the DNA fingerprinting test that was used was rapid, allowing us to get matching cases within 24-48 hours.
![](../index.jpg)
Regulation Changes of Pasteurized Products?
[Question: Did they change the regulations and the sale of pasteurized products or the labeling of pasteurized products?]
There are several issues in the food processing "dogma": One is that acidic products like apple or orange juice not have been a problem because E.coli O157:H7 grows poorly in an acidic environment. Unfortunately, this is incorrect, E.coli O157:H7 can grow well in an acidic environment. There have been previous outbreaks of E.coli related to apple juice where apples that fell into a cow pasture were used without being properly washed. On the other hand, the implicated producer in the 1996 outbreak was using state-of-the-art processing, except for pasteurization. Now they are pasteurizing their juices. However, defining pasteurization for all apple juices or all juices is difficult. There are FDA policy statements that juice should be pasteurized, but its application is more difficult.
1997 Hamburger Outbreak and Recall
What has happened in Washington State since the 1996 apple juice outbreak?
In 1997, there was an E.coli O157:H7 outbreak in Colorado, associated with contaminated hamburger. Although the number of human illnesses was relatively small, the resulting recall was nationwide, eventually involving 25 million pounds of beef. While we were on the periphery of this outbreak, there was pubic concern on whether contaminated beef was distributed in Washington State, and if there were human illnesses.
Because PFGE is a standardized method performed at the CDC and several state health departments, it is possible to perform direct comparisons of PFGE images tranmitted through the internet rather than having to mail and retest isolates. When we receive an image, our computer software searches our database for matches. In 1998, a communication sytem called Pulsenet connecting several states and the CDC was established. In 1997, Washington State was the first to establish such a connection.
Soon after the Colorado hamburger outbreak was identified and the recall initiated, PFGE profiles of involved strains were available at the CDC. The images were sent to Washington State through the internet, and our database was searched for similar patterns. No matches were found, which agreed with the initial distribution data for Washington State. Having two independent surveillance methods which agreed was reassuring. Each has its limitations. Surveillance data requires that ill people are tested for E.coli, and are reported to the health department. On the other hand, distribution data can be complex and changing as the recall is expanded.
![](../index.jpg)
Patterns of Outbreaks: Old versus New
A general comment about the patterns of outbreaks is that you can look at it as an old scenario outbreak and a new scenario outbreak.
Changing Scenarios for Food-borne Outbreaks |
Old |
New |
- "Church supper" or other event
- Error in food preparation
|
- Increase in "sporadic" cases
- Geographically dispersed
- Low attack rate
- Subtyping of strains often essential
- Traceback intergal part of investigation
- Dialogue with regulators, industry and academia essential to promote change
|
The old scenario outbreak is frequently involved single food item at a meal. The new scenario outbreak involves an increase in scattered cases around the country due to centralized food production and mass marketing.
![](../index.jpg)
Creative culture-based intervention
This is the Yakima Mexican-style Cheese Story. This represents another form of intervention that really needs to be considered in responses to food-borne outbreaks. There was a outbreak of about 60 or so cases of Salmonella in Yakima County related to Mexican-style cheese. Unpasteurized milk was being used to make the cheese. While it is illegal to buy and sell unpasteurized milk from almost all dairies, just saying that is not going to solve the problem. Many people are convinced that the raw milk cheese tastes better and certainly they were used to eating cheese from raw milk. In response, "Project Abuela,"(9) was started by Val Hillers and the agricultural extension program at WSU. First they studied who makes this cheese in Yakima County and found that there were about 225 cheese makers; all were small home operations and mostly run by elderly women. Hence the word abuela, which means "grandma" in Spanish. There was no single commercial operation. They then worked with some folks to develop a recipe for making Mexican-style cheese using pasteurized milk using buttermilk to put some bacteria into the milk, etc. They were able to produce a recipe for pretty good tasting Mexican-style cheese using pasteurized milk. They translated this recipe into Spanish and, with money from the dairy association, distributed aprons, measuring cups, thermometers etc., to 15 abuelas in Yakima County. They trained these women on the proper use of pasteurized milk to make Mexican-style cheese with the idea that these abuelas would in turn train other people in their community. They are doing a before and after study to see what effect has occurred. The important message is to work with the community and to find culturally acceptable alternatives which produce safer food.
![](../index.jpg)
Forthcoming Change: What needs to be done?
- Improve rapid diagnosis of potential food sources of an outbreak.
- Improve the ability to identify the exact place in the food processing chain where contamination occurred.
- Develop a system to be able to trace all food products from its point of origin to the final destination. This was useful in the 1996 apple juice outbreak where distribution patterns of the implicated lots matched with the distribution of human illnesses..
- Increase industry awareness of the necessity and importance of use of bar codes or other tracer mechanism for public health surveillance purposes.
- Develop and enhance community awareness of food-borne outbreaks.
- Develop creative programs to retrain local food producers in mechanisms to reduce the possibility of a food-borne outbreak.
References:
1. Bell BP, Goldoft M, Griffin PM, Davis MA, Gordon DC, Tarr PI, Bartleson CA, Lewis JH, Barrett TJ, Wells JG, Baron R, Kobayashi J "A Multistate Outbreak of Escherichia coli O157:H7 - Associated Bloody Diarrhea and Hemolytic Syndrome From Hamburgers: The Washington State Experience. JAMA 272:1349 November 2, 1994.
BACK
2. Riley LW, Remis RS, Helgerson SD, McGee HB, Wells JG, Davis BR, Hebert RJ, Olcott ES, Johnson LM, Hargrett NT, Blake PA, Cohen ML. Hemorrhagic colitis associated with a rare Escherichia coli serotype. N-Engl-J-Med. 1983 Mar 24. 308(12). P 681-5.
BACK
3. MacDonald KL, O'Leary MJ, Cohen ML, Norris P, Wells JG, Noll E, Kobayashi JM, Blake PA. "Escherichia coli O157:H7, an Emerging Gastrointestinal Pathogen: Results of a One Year Prospective Population Based Study." JAMA 259:3567 3570 June 24, 1988.
BACK
4. Ostroff SM, Griffin PM, Tauxe RV, Shipman LD, Greene KD, Wells JG, Lewis JH, Blake PA, Kobayashi JM. "A Statewide Outbreak of Escherichia coli O157:H7 in Washington State." American Journal of Epidemiology 132:239 1990.
BACK
5. Neill MA, Tarr PI, Clausen CR, Christie DL, Hickman RO. Escherichia coli O157:H7 as the predominant pathogen associated with the hemolytic uremic syndrome: a prospective study in the Pacific Northwest. Pediatrics. 1987 Jul. 80(1). P 37-40.
BACK
6. Tarr PI, Hickman RO. Hemolytic uremic syndrome epidemiology: a population-based study in King County, Washington, 1971 to 1980.Pediatrics. 1987 Jul. 80(1). P 41-5.
BACK
7. Gautom, RK Rapid pulsed-field gel electrophoresis protocol for typing of Escherichia coli O157:H7 and other gram-negative organisms in 1 day. J-Clin-Microbiol. 1997 Nov. 35(11). P 2977-80.
BACK
8. Outbreak of Escherichia coli O157:H7 infections associated with drinking unpasteurized commercial apple juice--British Columbia, California, Colorado, and Washington, October 1996. MMWR-Morb-Mortal-Wkly-Rep. 1996 Nov 8. 45(44). P 975.
BACK
9. Click here for a link to a description of the Abuela project.
Note: there is no return link...bookmark this page if you want to return.
BACK
Readings:
Armstrong, Gregory L. "Emerging Foodborne Pathogens: Escherichia coli 0157:H7 as a Model of Entry of a New Pathogen into the Food Supply of the Developed World." Epidemiologic Reviews, Vol. 18, No. 1, 1996, pp.29-51.
Return to Title PageHOME | List of Lectures