They’re recalling up to 500,000,000 eggs? Isn’t this an indictment of the U.S. egg industry as a whole?
It might be if that were the total production of the US, but it’s not even close. Last year, according to the U.S. Dept. of Agriculture’s National Agriculture Statistical Service, the 337, 000,000 laying hens living in the US produced 90,400,000,000 eggs (about 269 eggs per layer, by the way). The recalled number of eggs is less than 1% of the national output, and even among those 500,000,000, it is likely that only a tiny percentage are actually infected. Statistically, the odds are about 1 egg out of 20,000 eggs is infected. ( www.eggsafety.org )
I hear that thousands of people have been made ill from these eggs: what are my chances that I will get salmonella from eating eggs?
As a rule, you are right in thinking that it is possible to get salmonella from eating undercooked eggs, and this is unfortunately one of the most common ways to get salmonella. However the odds are vastly on your side as opposed to being on salmonella’s. In a 2008 paper (Davis et al, cited below) the odds were given as 1 or 2 people out of 100,000 will get salmonella from undercooked eggs.) This seems a tad too rare, so let’s divide up the estimated 2010 population of the U.S., 308,000,000, by the FDA’s estimate that there are 142,000 cases annually of salmonella caused by eating undercooked eggs. This gives you a 1 in 2168 chance of getting undercooked-egg-induced salmonella. That’s cases of illness, not fatalities. Out of this small number, your chances of actually dying admittedly increase if you are elderly, an infant, or immunocompromised, and pasteurized egg products available to foodservice providers are recommended for venues where large numbers of these groups are served. But remember, the odds of becoming ill or dying from salmonella derived from eggs would be essentially zero if the eggs were cooked thoroughly, by the way.
What causes this contamination?
A strain of bacteria called Salmonella enteritidis.
Where does that bacterium come from?
It can come from soil, water, or feed, but is found today mostly in poultry manure. It appears to have migrated from rats and mice to poultry a few decades ago. Egg producers and government scientists and health officials have since placed a premium on detecting any signs of rodents in egg producing operations, and in eliminating the vermin, but to some extent the bad genie is out of the bottle. Rodent control still limits the chances of new acute outbreaks of subtypes that have yet to infect layers or show up in eggs.
How does the salmonella get into the egg?
Salmonella enteritidis most commonly lives in the reproductive and intestinal tracts of layers . Eggs are made “inside out” in the sense that whatever pathogens live inside the hen can be transmitted to the eggs growing inside her during egg formation and laying.
Are all parts of the egg equally “dangerous.”
As a practical matter, given that eggs come out of the hen from the same place as her manure, the shell is by far, the most likely part to be contaminated, as it traverses this shared route. This is followed at a great statistical distance by the egg white, which just happens to have naturally produced inhibitors of the further growth of salmonella (Humphrey & Whitehead 1993) and then, accounting for an even tinier percentage, would be the yolk.
What do egg producers do to make sure the eggs are safe?
First and foremost, eggs and flocks are tested on a regular basis and layers known to be salmonella carriers are taken out of production, and their eggs stopped from entering the market. In some cases, the layers will be given antibiotics until the infection clears. (In other cases, the layers will be destroyed outright.) Any eggs from those layers will be discarded, and even when the infection has passed in successfully treated layers, the eggs will not be put back into the food supply until the eggs themselves have tested free of antibiotics.
The day-to-day processing of eggs also involves a number of important, practical safety steps. All shell eggs are thoroughly washed to remove fecal traces. New procedures involving ozone (Perry, Rodriguez-Romo & Yousef 2008), and microwaves (Lakins et al 2008) are being developed as boosters in egg contaminant removal. Eggs are kept constantly chilled, a seemingly simple step that greatly retards the growth of virtually all bacterial pathogens, including salmonella.
The living conditions of the hens are also continuously inspected and cleaned. The chicken feed and water supply are examined. In all cases of conscientious egg production, the goal is to get the fecal matter away from the birds and the newly laid eggs as often as possible.
I hear that many US Producers do not vaccinate their hens, while this is done routinely in other countries. What gives?
A New York Times story headlined “U.S. Rejected Hen Vaccine Despite British Success,” and reported by William Neuman on August 25, 2010, called into question the fact that many U.S. egg producers do not vaccinate their hens in the same way that British egg producers did, virtually eliminating egg-associated salmonella cases over there. But a more careful reading of the story also indicated that the FDA had considered it, but decided that the evidence was not so clear cut as to mandate it nationally. (It’s important to note that the Brits still find salmonella within their hen houses and on the grounds of their farms, and even in some chickens and eggs, and about 500 cases of egg-associated salmonella in humans still crop up annually, although that number represents a dramatic drop off .) The FDA had already mandated a number of enhanced hygiene practices on July 9, 2010, for the egg industry before the outbreak, so it is not as if, the agency has been asleep at the switch. The FDA and the industry’s leading trade organization, the United Egg Producers, have been partners in safety for decades, according to the FDA’s own pronouncements. A recent review of Britain’s success (Snow et al. 2010) cited vaccination as one of the likely reasons, but it also cited washing and disinfecting the hen house, providing cleansing pools of disinfectant and scrub brushes so that workers could remove poultry manure from their shoes and boots, using a commercial chicken feed supplier as opposed to a home-grown mixture , and the presence of cats and dogs to keep the rodent population down as other contributors. While it is not clear whether or not the much larger US egg production facilities use cats and dogs to hunt rodents on site, measure like these are already standard here.
US egg-producing facilities are gigantic and involve caged-birds, and operations like this are banned in Europe, including within the UK. Will freeing the layers free us from salmonella in their eggs?
According to an August 25, 2010 column by Angela Wu in Newsweek entitled “Are Free-Range Eggs Safer: Factory farming has its problems, but evidence is unclear about whether local food is better,” the story is complicated and the evidence contradictory. The problem is that the FDA has found salmonella outbreaks at the largest factory farms and at some of the smallest free-range operations, as well as in those mid-sized operations in between. Two pieces of evidence will surprise the back-to-nature enthusiasts: In large caged bird operations, by their very design, manure removal is done more often and much more efficiently: the birds don’t get to soil themselves or the eggs to the same degree. Second, free-range, “pastured” poultry actually has a higher rate of parasitic infections, so one might wish not to trade the devil you know (salmonella) for the devil you don’t.
Should I give up eating eggs until this is all over?
If you did, you would be giving up one of the most economical, nutritious, and still generally very safe sources of protein, vitamins, minerals, and nutraceuticals. Much wiser might be following the recommendations of a paper by Davis et al 2008, in which they compare common means of cooking eggs at home in terms of their ability to kill off salmonella (which, ironically because they could not find enough naturally infected eggs, with which to conduct this experiment, they had to go out and artificially infect them). They concluded that hard-boiled, soft-boiled, and eggs poached in dimpled pan suspended over the boiling water and/or steam were safest. Over-easy and scrambled eggs were reasonably safe, with longer cooking times adding to the margin of safety. “Dropped poached eggs,” meaning those let freely slip into simmering boiling or near/boiling water were safe but only if they were immersed for at least 5 minutes. Sunny side eggs, were, alas, the least safe, although increased cooking time (until the yolk is firmly set) and the use of a pan cover or basting of the yolk with hot cooking oil or grease was thought to be helpful to get the top of the yolk to cook through.
Tony Stankus, FSLA email@example.com Life Sciences Librarian, Science Coordinator & Professor
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