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Wednesday, June 3, 2009
1. What is foodborne illness?
The way food is processed and prepared is important because all foods have the ability to carry microorganisms (like bacteria and viruses) or toxins that can cause illness. If microorganisms or toxins are introduced to food or if bacteria are allowed to grow in or on food without being killed (usually by heat) before eating, foodborne illness can result. Common symptoms of foodborne illness include nausea, vomiting, diarrhea, cramps and headache.
2. How safe are eggs?
The risk of getting a foodborne illness from eggs is very low. However, the nutrients that make eggs a high-quality food for humans are also a good growth medium for bacteria. In addition to food, bacteria also need moisture, a favorable temperature and time in order to multiply and increase the risk of illness. In the rare event that an egg contains bacteria, you can reduce the risk by proper chilling and eliminate it by proper cooking. When you handle eggs with care, they pose no greater food-safety risk than any other perishable food.
The inside of an egg was once considered almost sterile. But, over recent years, the bacterium Salmonella enteritidis (Se) has been found inside a small number of eggs. Scientists estimate that, on average across the U.S., only 1 of every 20,000 eggs might contain the bacteria. So, the likelihood that an egg might contain Se is extremely small – 0.005% (five one-thousandths of one percent). At this rate, if you're an average consumer, you might encounter a contaminated egg once every 84 years.
Other types of microorganisms could be deposited along with dirt on the outside of an egg. So, in the U.S., eggshells are washed and sanitized to remove possible hazards. You can further protect yourself and your family by discarding eggs that are unclean, cracked, broken or leaking and making sure you and your family members use good hygiene practices, including properly washing your hands and keeping them clean.
3. Are eggs the only source of Salmonella bacteria?
No. Salmonella bacteria are widely found in nature and easily spread. The bacteria can be found in the intestinal tracts of animals, birds, reptiles, insects and people. While the egg itself may not be contaminated when you buy it, it can become contaminated from various sources, such as hands, pets, other foods and kitchen equipment, too.
4. Doesn't the eggshell protect an egg from bacteria?
Yes and no. The egg has many natural, built-in barriers to help prevent bacteria from entering and growing. These protect the egg on its way from the hen to your home. But, although it does help, the porous shell itself is not a foolproof bacterial barrier. For further safety, government regulations require that eggs be carefully washed with special detergent and sanitized. Then, the hen's original protective shell coating is generally replaced by a thin spray coating of a tasteless, odorless, harmless, natural mineral oil. A shiny shell indicates oiling, rather than an unsafe or old egg.
Other protective barriers include the shell and yolk membranes and layers of the white which fight bacteria in several ways. The structure of the shell membranes helps prevent the passage of bacteria. The shell membranes also contain lysozyme, a substance that helps prevent bacterial infection. The yolk membrane separates the nutrient-rich yolk from the white.
In addition to containing antibacterial compounds such as lysozyme, layers of the white discourage bacterial growth because they are alkaline, bind nutrients bacteria need and/or don't provide nutrients in a form that bacteria can use. The thick white discourages the movement of bacteria. The last layer of white is composed of thick ropey strands which have little of the water that bacteria need but a high concentration of the white's protective materials. This layer holds the yolk centered in the egg where it receives the maximum protection from all the other layers.
Are Salmonella bacteria most likely to be found in the egg's white or yolk?
Bacteria, if they are present at all, are most likely to be in the white and will be unable to grow, mostly due to lack of nutrients. As the egg ages, however, the white thins and the yolk membrane weakens. This makes it possible for bacteria to reach the nutrient-dense yolk where they can grow over time if the egg is kept at warm temperatures. But, in a clean, uncracked, fresh shell egg, internal contamination occurs only rarely.
7. Does a blood spot mean an egg is contaminated?
No. You can't see bacteria with the naked eye. Blood or meat spots are occasionally found on an egg yolk and are merely an error on the part of the hen. They're caused by the rupture of a blood vessel on the yolk surface when it's being formed or by a similar accident in the wall of the oviduct. Most eggs with blood spots are detected by electronic spotters and never reach the market. But, even with mass scanners, it's impossible to catch them all. Both chemically and nutritionally, eggs with blood spots are fit to eat. You can remove the spot with the tip of a knife, if you wish.
8. Are the twisted, ropey strands of egg white safe?
Yes. These strands are the chalazae which anchor the yolk in the center of the thick white. They're composed of nutritious egg albumen and do not indicate contamination. In fact, the more prominent the chalazae, the fresher the egg. These natural parts of the egg don't interfere with cooking or beating of the white and you don't need to remove them, although some cooks like to strain them from stirred custard.
9. What will happen if I eat an egg containing Salmonella?
If an egg containing Salmonella has been kept refrigerated and someone who uses good hygiene practices serves it to you immediately after proper cooking, you'll simply have a nutritious meal. If the egg has been improperly handled, though, you might experience the foodborne illness called salmonellosis. You could have symptoms of abdominal cramps, diarrhea, nausea, vomiting, chills, fever and/or headache within 6 to 72 hours after eating. The symptoms usually last only a day or two in healthy people but can lead to serious complications for the very young, pregnant women, the elderly, the ill and those with immune system disorders. Anyone who has had salmonellosis may pass along the bacteria for several weeks after recovering, but salmonellosis is seldom fatal. While the risk of getting salmonellosis is very small, there's no need to take chances because cooking kills Salmonella.
10. What usually causes salmonellosis?
Salmonellosis outbreaks are most often associated with animal foods, including chicken, eggs, pork and cheese, but have also been reported related to cantaloupe, tomatoes, alfalfa sprouts, orange juice and cereal among other foods. Human carriers play a big role in transmitting some types of salmonellosis. Salmonella bacteria can easily spread from one food to another, too.
The majority of reported salmonellosis outbreaks involving eggs or egg-containing foods have occurred in foodservice kitchens and were the result of inadequate refrigeration, improper handling and insufficient cooking. If not properly handled, Salmonella bacteria can double every 20 minutes and a single bacterium can multiply into more than a million in 6 hours. But, properly prepared egg recipes served in individual portions and promptly eaten are rarely a problem. You can ensure that your eggs will maintain their high quality and safety by using good hygiene, cooking, refrigeration and handling practices.
11. What is being done about Salmonella in eggs?
The egg industry, the public health community and government agencies have been working diligently to deal with Salmonella enteritidis.
Egg industry programs start by keeping breeder flocks free of Salmonella. Ongoing research is dedicated to discovering how Se gets into flocks and how it might be blocked. The industry also uses strict quality-control practices and sanitation procedures all through production, processing and preparation. This includes testing chicks to be sure they're free of Salmonella, bio-security (such as washing and sanitizing not only the eggs, but facilities, too) and other measures. To block Se from multiplying in the egg in the rare event it's present, eggs are held at cool temperatures following packing and throughout transportation. Important, too, are industry education programs which encourage food preparers to use safe food-handling practices.
Along with state representatives, the United States Department of Agriculture (USDA) and the Food and Drug Administration (FDA) are developing new national standards with the aim of reducing and eventually eliminating egg-related salmonellosis. The strategies will include a scientific, risk-based, farm-to-table plan covering production, processing, transport, storage, retail handling and delivery. The plan will also include education on the responsibilities of consumers, inspectors and food handlers at all levels.