Last week's recall of 380 million eggs because of salmonella could be in part attributed to wet, humid weather across Iowa, which could have contaminated chicken feed.
The FDA said on Thursday afternoon that samples of chicken feed collected from the two Iowa producers where the outbreak has been traced tested positive for the same strand of salmonella found in the tainted eggs.
An increase in salmonella itself is not linked directly with weather and climate, but the rodent population responsible for spreading salmonella is influenced by changes in temperature, precipitation and season.
Very wet weather, humid conditions, and seasonal changes bringing cooler temperatures can drive rodents into chicken houses, which act as a port of shelter from the elements.
"In the fall, when the weather turns cold, rodents move into buildings," said Darrell Trampel, Iowa State University Professor of Veterinary Diagnostics.
Wright County Eggs of Galt, Iowa, where the recalled eggs originated, is in a region that has been inundated by above-normal rainfall this summer.
AccuWeather.com meteorologists note that Galt, Iowa, is in an area inflicted by rainfall 200 to 300 percent above normal since June 1. This translates into approximately 8-12 inches of extra rainfall for Galt this summer.
Cities around Galt, including Waterloo, Des Moines and Marshalltown, have had over 20 inches of rain since June 1. The Midwest has endured above-normal temperatures and extreme humidity this summer.
Excess rainfall could have caused more rodents to enter the chicken coops in Iowa, which could mean more salmonella-infected droppings. The infected droppings could have contaminated the feed eaten by the chickens producing the eggs.
According to a Penn State College of Agricultural Sciences manual on food safety in the table egg industry, pest management is a critical control point for diminishing salmonella exposure in chickens.
"Rodents are the primary source of salmonella," said Trampel. "They bring it with them into the chicken houses."
The report said that rodents like mice and rats are among the leading causes of salmonella in chicken coops because their daily droppings can contain up to 230,000 salmonella bacteria.
When excreting, rodents often leave their droppings in feed troughs, on egg belts and in other areas where there is contamination of not only eggs, but the feed eaten by chickens.
This map shows that Galt, Iowa, (noted by the "X") is in an area inflicted by rainfall 200 to 300 percent above normal since June 1. Image courtesy of the National Weather Service (NWS).
Salmonella can infect eggs in two different ways. The bacterium can latch onto the actual eggshell when in contact with rodent droppings.
In the United States, eggs are washed and sanitized before going to stores.
Salmonella can also be ingested by the chicken after eating food contaminated with the infected rodent defecation. In this case, the inside of the egg can have salmonella.
The latest recall of nearly 400 million eggs occurred because of salmonella inside the egg.
While salmonella inflicting the outer portion of an egg is easy to be tested for and distinguished, internal salmonella is much more difficult to detect.
"There currently are no methods to see if salmonella has infected the egg internally without cracking it," said Dr. Stephanie Doores, Associate Professor of Food Science for Penn State.
Salmonella is the leading cause of food-borne illness in the United States.
Dr. Paul Patterson, of Penn State, specializes in egg production, quality and safety. He said that improper handling and cooking of eggs are the major factors in human salmonella infections.
"Proper cooking will destroy salmonella, it would not be an issue," he said.
Patterson said that the size of the recall was most likely a cautionary measure. He also said that he credited the Iowa company for taking action with its voluntary recall.
Content contributed by Jesse Ferrell, AccuWeather.com Meteorologist.
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