Is there a link between <i>E. coli</i> outbreaks and time of year?
Is there a link between <i>E. coli</i> outbreaks and time of year?
Fact: Nineteen of the 22 E. coli 0157:H7 discoveries associated with leafy greens that have resulted in confirmed illnesses since 1995 took place in late summer or early fall.
Is there something about the hot summer months that creates an environment that is more likely to produce this specific strain of E. coli? Is the pathogen itself temperature-sensitive? Is there something about animals, which are known carriers and suspected spreaders of the pathogen, that makes them more susceptible to E. coli when they are heat stressed? Is 19 out of 22 statistically meaningful or too small of a sample to be significant? Robert Mandrell, who is a food-safety and microbiological researcher with the U.S. Department of Agriculture's Agricultural Research Service at its Western Regional Research Center in Albany, CA, said that the timing of the E. coli 0157:H7 contaminations over the past dozen years is very interesting and deserves study.
He was also willing to speculate as to some of the potential reasons that the outbreaks seemed to have clustered around August, September and October. But he also said often during the 30-minute interview with The Produce News that it is "all speculation."
There have been no studies about this particular E. coli strain that shine any light on the situation, said Mr. Mandrell, who is part of a team that recently received a $5 million grant from USDA to research E. coli 0157:H7 with respect to the leafy green industry. He said that the research would look to see if seasonality plays a role. If seasonality is significant, he said there are a number of potential reasons for this that do need to be put to the test.
On its face, 19 out of 22 outbreaks confined to just a few months does seem to the layman to be significant. But Mr. Mandrell said that might not be the case. He said that one could shuffle a deck of cards and the first 10 could all come up as a red suit. Assuming it is a standard deck, it is known that of the next 42 cards, the majority is going to be a black suit. The first 10 cards were not a predictor of the future but just a coincidence.
With that reasoning in mind, it is possible -- and not even unlikely -- that given another 22 outbreaks, the pattern would be vastly different, rendering the seasonality of the first 22 outbreaks insignificant.
"A sample size of 22 might well be statistically insignificant," he said.
But it is interesting nonetheless, especially in light of the fact that it seems counter-intuitive to some of the early research that has been done with regard to seasonality.
Mr. Mandrell said that there has been some testing on the river and canal water in the Salinas Valley area where most of the outbreaks over the past 12 years originated. Those preliminary tests show that there does appear to be an increased level of E. coli in the water immediately following a rainfall. One could logically speculate that the increased levels of E. coli in the rivers and canals after a rainfall are a direct result of the washing of the hillsides into the water. It is not a giant leap to suspect that rainfall can wash E. coli- carrying animal feces into the water.
But logic and a study of the weather patterns reveal that rainfall would have an impact in the spring rather than the late summer or early fall, when rainfall is at a minimum or non-existent.
Animals are known carriers of E. coli 0157:H7. In fact, in the E. coli outbreak of 2006, cattle and wild pigs in the area of the farm where the contaminated spinach was grown did test positive for the exact strain of E. coli found in people that became ill.
Mr. Mandrell said that while it has not been proven without a doubt, it does seem highly likely that the cattle or wild pigs contaminated the spinach rather than the other way around. "We know it is the same strain and the cattle were in a confined area. They did not have access to the spinach."
Many have speculated that the spinach was contaminated by the wild pigs or possibly by birds, which were carriers of the feces from the animals in the nearby grazing land to the spinach field.
Continuing to speculate as to why summer conditions might be an issue, Mr. Mandrell said that plant debris is another potential source of the pathogen. By the end of the summer, there is more plant debris in the field, and this could potentially be a good environment for the pathogen to grow. In the laboratory, Mr. Mandrell said that E. coli 0157:H7 has shown that, like most pathogens, heat and moisture can facilitate growth, hence the heat of the summer may play a role. But he said no one has yet tested what role UV light might play in the growth of this E. coli strain.
Mr. Mandrell said it is also possible -- but again only speculation -- that increased heat stress makes animals more susceptible to having the E. coli pathogen produced in large numbers within their systems. "We do need to look at wildlife and see what role they might play."
The researcher said that extensive research by the beef industry has shown that cattle are known carriers of E. coli 0157:H7. Combine that research with the fact that the same strain was found in cattle, wild pigs and the spinach in the 2006 outbreak, and logic indicates that there is a connection.
He said that in studying the environment, one must also look at what might be inherent in the plant or the area that might attract a greater concentration of wild animals at the end of the summer. For example, Mr. Mandrell said, it is known that wild pigs are attracted to grape vines. The wine industry in the Salinas Valley has grown exponentially in recent years, and the grapes are typically hitting maturity in the late summer time period. "Might that play a role?" Mr. Mandrell asked rhetorically.
He reiterated that there is abundant speculation having to do with the seasonality of E. coli 0157:H7, but it may not be verifiable, especially in the short term. Mr. Mandrell said that much of the E. coli research that he will be conducting are long-range in nature. Of course, to the industry, 22 outbreaks that resulted in human illness over the past 12 years are too many incidences. But to researchers, it just may be too few to produce sound scientific judgments.
Mr. Mandrell said that the E. coli-spinach connection in 2006 was the very first time that the strain of illness found in humans was traced back, through genetic fingerprinting, to a specific field and to animals in the general vicinity of that field.
To find the true cause of the E. coli O157:H7 contaminations, one may need many more outbreaks that can be traced back to their roots. And of course, the leafy greens industry is doing everything in its power so that researchers don't have more pieces of the puzzle with which to work.
Is there something about the hot summer months that creates an environment that is more likely to produce this specific strain of E. coli? Is the pathogen itself temperature-sensitive? Is there something about animals, which are known carriers and suspected spreaders of the pathogen, that makes them more susceptible to E. coli when they are heat stressed? Is 19 out of 22 statistically meaningful or too small of a sample to be significant? Robert Mandrell, who is a food-safety and microbiological researcher with the U.S. Department of Agriculture's Agricultural Research Service at its Western Regional Research Center in Albany, CA, said that the timing of the E. coli 0157:H7 contaminations over the past dozen years is very interesting and deserves study.
He was also willing to speculate as to some of the potential reasons that the outbreaks seemed to have clustered around August, September and October. But he also said often during the 30-minute interview with The Produce News that it is "all speculation."
There have been no studies about this particular E. coli strain that shine any light on the situation, said Mr. Mandrell, who is part of a team that recently received a $5 million grant from USDA to research E. coli 0157:H7 with respect to the leafy green industry. He said that the research would look to see if seasonality plays a role. If seasonality is significant, he said there are a number of potential reasons for this that do need to be put to the test.
On its face, 19 out of 22 outbreaks confined to just a few months does seem to the layman to be significant. But Mr. Mandrell said that might not be the case. He said that one could shuffle a deck of cards and the first 10 could all come up as a red suit. Assuming it is a standard deck, it is known that of the next 42 cards, the majority is going to be a black suit. The first 10 cards were not a predictor of the future but just a coincidence.
With that reasoning in mind, it is possible -- and not even unlikely -- that given another 22 outbreaks, the pattern would be vastly different, rendering the seasonality of the first 22 outbreaks insignificant.
"A sample size of 22 might well be statistically insignificant," he said.
But it is interesting nonetheless, especially in light of the fact that it seems counter-intuitive to some of the early research that has been done with regard to seasonality.
Mr. Mandrell said that there has been some testing on the river and canal water in the Salinas Valley area where most of the outbreaks over the past 12 years originated. Those preliminary tests show that there does appear to be an increased level of E. coli in the water immediately following a rainfall. One could logically speculate that the increased levels of E. coli in the rivers and canals after a rainfall are a direct result of the washing of the hillsides into the water. It is not a giant leap to suspect that rainfall can wash E. coli- carrying animal feces into the water.
But logic and a study of the weather patterns reveal that rainfall would have an impact in the spring rather than the late summer or early fall, when rainfall is at a minimum or non-existent.
Animals are known carriers of E. coli 0157:H7. In fact, in the E. coli outbreak of 2006, cattle and wild pigs in the area of the farm where the contaminated spinach was grown did test positive for the exact strain of E. coli found in people that became ill.
Mr. Mandrell said that while it has not been proven without a doubt, it does seem highly likely that the cattle or wild pigs contaminated the spinach rather than the other way around. "We know it is the same strain and the cattle were in a confined area. They did not have access to the spinach."
Many have speculated that the spinach was contaminated by the wild pigs or possibly by birds, which were carriers of the feces from the animals in the nearby grazing land to the spinach field.
Continuing to speculate as to why summer conditions might be an issue, Mr. Mandrell said that plant debris is another potential source of the pathogen. By the end of the summer, there is more plant debris in the field, and this could potentially be a good environment for the pathogen to grow. In the laboratory, Mr. Mandrell said that E. coli 0157:H7 has shown that, like most pathogens, heat and moisture can facilitate growth, hence the heat of the summer may play a role. But he said no one has yet tested what role UV light might play in the growth of this E. coli strain.
Mr. Mandrell said it is also possible -- but again only speculation -- that increased heat stress makes animals more susceptible to having the E. coli pathogen produced in large numbers within their systems. "We do need to look at wildlife and see what role they might play."
The researcher said that extensive research by the beef industry has shown that cattle are known carriers of E. coli 0157:H7. Combine that research with the fact that the same strain was found in cattle, wild pigs and the spinach in the 2006 outbreak, and logic indicates that there is a connection.
He said that in studying the environment, one must also look at what might be inherent in the plant or the area that might attract a greater concentration of wild animals at the end of the summer. For example, Mr. Mandrell said, it is known that wild pigs are attracted to grape vines. The wine industry in the Salinas Valley has grown exponentially in recent years, and the grapes are typically hitting maturity in the late summer time period. "Might that play a role?" Mr. Mandrell asked rhetorically.
He reiterated that there is abundant speculation having to do with the seasonality of E. coli 0157:H7, but it may not be verifiable, especially in the short term. Mr. Mandrell said that much of the E. coli research that he will be conducting are long-range in nature. Of course, to the industry, 22 outbreaks that resulted in human illness over the past 12 years are too many incidences. But to researchers, it just may be too few to produce sound scientific judgments.
Mr. Mandrell said that the E. coli-spinach connection in 2006 was the very first time that the strain of illness found in humans was traced back, through genetic fingerprinting, to a specific field and to animals in the general vicinity of that field.
To find the true cause of the E. coli O157:H7 contaminations, one may need many more outbreaks that can be traced back to their roots. And of course, the leafy greens industry is doing everything in its power so that researchers don't have more pieces of the puzzle with which to work.
