Research Links Grade A Eggs to Food Poisoning
By WARREN E. LEARY, Special to the New York Times
Published: April 8, 1988
WASHINGTON, April 7— Clean, inspected Grade A eggs may be responsible for a recent increase in salmonella food poisoning in the Northeast, and consumers should be cautious about eating raw or undercooked eggs, Federal researchers said today.
Evidence that cleaned and disinfected eggs in their shells may be a source of infection raises the possibility that the contamination originates inside infected chickens and is passed to immature eggs before the shell forms, said the researchers from the Centers for Disease Control in Atlanta.
The scientists said that while the risk of infection is slim, those at high risk of severe illness and death from food poisoning should avoid raw eggs or undercooked egg dishes and should use pasteurized bulk eggs. High-risk groups include the elderly, infants under one year of age and those whose immune systems are compromised by disease or anticancer treatments.
The scientists emphasized, however, that all of the investigated outbreaks involved people eating raw or undercooked eggs, and there is no need for people to stop eating eggs.
Grade A eggs are washed and treated with a disinfectant to remove salmonella that may be present in the feces of chicken.
Until salmonella contamination can be eliminated from flocks or the eggs they produce, particularly in the Northeastern United States, the authors said, ''The use of pasteurized eggs in high-risk settings such as nursing homes and in commercial foods that may not be adequately cooked before eating may provide an added margin of safety.''
Dr. Michael E. St. Louis and colleagues at the disease centers reported their findings in the April 8 issue of The Journal of the American Medical Association. They said eggs had been implicated in a surprising number of the 65 outbreaks of Salmonella enteritidis reported in the Northeast from January 1985 to May 1987. The outbreaks involved 2,119 cases and 11 deaths. Of the 35 outbreaks with identified food sources, 77 percent were caused by eggs or foods containing eggs.
While this type of salmonella is identified in less than 10 percent of all salmonella poisoning cases nationwide, it accounts for almost 30 percent of such cases in Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island and Vermont.
''Next to Salmonella typhimurium, Salmonella enteritidis is the second leading type that causes human disease,'' Dr. St. Louis said in a telephone interview, ''but in certain Northeast states, it's the leading cause.'' New Strain Is Indicated
The sudden rise of this type of salmonella in one part of the country could indicate that a new strain of the organism has developed that is transmitted differently, and scientists are studying this possibility, he added.
Salmonella bacteria are a major cause of illness worldwide. Infected livestock, poultry and raw milk are common sources of the bacteria. Eggs and egg products have also been cited often as a source of Salmonella, but in the past the infection has usually been linked to cracked or dirty eggs.
Symptoms of salmonella include nausea, abdominal cramps, diarrhea, fever and sometimes vomiting. Symptoms usually appear 12 to 48 hours after ingestion of contaminated food. The disease is usually mild, lasting one to four days, but salmonella occasionally produces severe and protracted symptoms. It is particularly dangerous in infants and the elderly.
Treatment usually is limited to fluids and a bland diet although doctors sometimes prescribe antibiotics to patients at higher risk for complications. Advice on Killing Bacteria
In an interview, Dr. St. Louis said it was important that consumers cook eggs properly to kill any of the bacteria present, which means raising the internal temperature of eggs to 140 degrees Fahrenheit for three and a half minutes.
To reach these temperatures, eggs must be boiled for seven minutes, poached for five minutes or fried on each side for three minutes. The authors noted that no duration of frying on one side - making eggs ''sunny-side up'' - was sufficient to kill all of the bacteria. No data was available on microwave cooking to determine an optimum cooking time.
The study noted that raw or undercooked eggs are frequently used in Caesar salad dressing, hollandaise sauce, eggnog, homemade ice cream, homemade mayonnaise and many other foods. Commercial versions of these products use pasteurized eggs and are free of contamination, Dr. St. Louis said. Bulk eggs and frozen egg substitutes made from egg whites also have been sterilized and are readily available., Dr. St. Louis said.
Commercial versions of these products use pasteurized eggs and are free of contamination, and bulk eggs and frozen egg substitutes made from egg whites also have been sterilized and are readily available, Dr. St. Louis said.
Cathy McCharen, a spokeswoman for the egg industry-financed Egg Nutrition Center in Washington, called the cooking times in the report ''ridiculously long'' because the eggs in the study were artificially inoculated with higher levels of bacteria than would normally be found in nature.
She also said the salmonella outbreak discussed in the research appeared to be over and that no problems have been seen in the Northeast for months. She asserted that industry programs to control salmonella contamination in eggs supplies are working and the key to stopping future outbreaks is for consumers to properly store, handle and cook eggs.
Ms. McCharen said there was no evidence that contaminated chickens could infect the yolks of eggs before the shells are formed and that the C.D.C. researchers had only established a statistical link between some, but not all, of the Northeastern salmonella outbreaks and eggs.