The nation's largest outbreak of food poisoning in the last five years has been attributed to contaminated eggs that were undercooked and then mishandled, according to a recently released federal study.
More than 435 people became ill during the first week of October at a Chicago convention banquet for 1,900, a Centers for Disease Control newsletter stated in an analysis of the incident.
Local health officials who investigated the episode discovered that eggs used in a bread pudding with vanilla sauce have been implicated as the source of Salmonella enteriditis, a harmful bacteria believed to have caused the illnesses and a resulting 147 hospitalizations. No deaths were reported.
The CDC report is a major setback for the egg industry and the federal government, which have had only limited success controlling the spread of salmonella in the nation's egg supply.
The actual number of conventioneers who experienced salmonella-like symptoms--vomiting, diarrhea, abdominal cramps, fever--is thought to be much higher than the current figure, according to officials.
"The number '435' was obtained by counting those that received emergency room treatment that we knew of . . . There could have been a lot more," said Dr. Ban Mishu, medical epidemiologist with the CDC's bacterial diseases division. "There may have been some who sought medical treatment that we didn't know about and some who didn't seek medical treatment at all . . . Or received it after they left Chicago."
In the coming weeks, the Illinois Public Health Department will survey all those who attended the Hyatt Regency banquet to determine more accurately the total number of illnesses. During the peak of the outbreak, 97% of the victims tested for the bacterium were found to have contracted S. enteriditis, a strain of salmonella that is generally associated with raw or undercooked eggs.
"The implicated dessert was prepared with grade AA shell eggs and may have been undercooked," the CDC report stated. "In addition, the dessert was left at room temperature for 1 (to) 4 hours between cooking and serving."
An egg industry representative was critical of the way health officials handled the outbreak and the subsequent reports of the incident.
"There was a very confusing investigation (conducted) and it was hard to pinpoint what food (caused the illnesses)," said Cathy McCharen, director of the Egg Nutrition Center in Washington. "Statistically, (data) pointed to the bread pudding but others at the banquet were served undercooked chicken."
There has been a dramatic increase in the number of S. enteriditis cases since the early '80s, many of which have been linked to the consumption of raw or undercooked eggs, according to the CDC. The first cluster of cases was concentrated in the Northeastern United States, but incidences have since spread to other parts of the country, including the Midwest. California producers claim that this state's egg-laying flock is relatively free of S. enteriditis compared to other regions.
"(Between) 1985 and 1989, state . . . health departments reported 244 S. enteriditis outbreaks, which accounted for 8,607 cases of illness, 1,094 hospitalizations and 44 deaths. Of the 109 outbreaks in which a food vehicle was identified, 89 (or 82%) were associated with shell eggs," the CDC stated in its "Morbidity and Mortality Weekly Report."
McCharen of the Egg Nutrition Center said that eggs are not the only source of S. enteriditis and that it is found in other foods such as chicken and beef.
Since the Chicago outbreak, health officials have traced the eggs used at the Hyatt Regency banquet to a large producer in Indiana, where S. enteriditis has been isolated from all the chicken houses, or growing environments, tested. As a result, federal regulations mandate that the producer must pasteurize the eggs before selling them. (Pasteurized egg products are available only to commercial and institutional customers, not the general public.)
Researchers believe that S. enteriditis becomes lodged in the bloodstream of egg-laying hens and is thus found in the heart, lungs and ovary. When the yolk is created, the salmonella is already present, or even before the shell is formed.
"Once the egg is laid by the hen it is then perfectly good-looking but is still contaminated," said the CDC's Mishu. "You can't wash it off." Mishu added that cooking eggs properly would destroy any organism present.
The CDC estimates that one egg in 10,000 contains S. enteriditis.
"If it is true that the average American eats 250 shell eggs per year, then 2% of the population is exposed to these (potentially contaminated) eggs," Mishu said.
Several groups are at particular risk for Salmonellosis: infants, the elderly, pregnant women and immuno-compromised individuals such as cancer and AIDS patients. For instance, residents of hospitals and nursing homes have suffered from S. enteriditis on a disproportionate basis.