Raw eggs used in homemade ice cream have been implicated as the source of a food poisoning outbreak in Kern County, according to state health officials.
The episode is one of the largest such contamination incidents linked to raw or undercooked eggs in California since a series of similar outbreaks began occurring in the northeastern United States during the past several years.
A recently released report by the California Department of Health Services details how more than a dozen people contracted salmonellosis at a potluck birthday party.
The data accumulated is said to be sound because the investigation began soon after those attending the event sought medical treatment. As a result, some of the food served at the affair was still available for laboratory testing.
"Of the 39 who attended the birthday party . . . 14 (or about 36%) reported illness. The most common symptoms were abdominal pain, anorexia, fever and diarrhea," according to the department's Infectious Disease Branch, which prepared an account of the incident.
Although everyone who became ill in this instance eventually recovered, salmonellosis can be severe and often requires hospitilization. In rare cases it is fatal. Those groups especially vulnerable to the bacteria include infants, the elderly, pregnant women and those whose immune systems are compromised, such as cancer or AIDS patients.
In reviewing the episode, health officials conducted food histories and a series of medical tests on the patients. Upon completion, investigators found that strawberry ice cream was the most likely contamination vehicle as it was consumed by 81% of the victims.
Salmonella typhimurium, a harmful bacteria, was also isolated from the dessert. Raw eggs used to prepare the ice cream were identified as the probable source of the contamination.
The event, which occurred last August, is distinguished in a number of ways.
Namely, Salmonella enteritidis had been the bacteria most commonly associated with raw eggs. In fact, during the past few years federal officials have reported that several thousand people in the northeastern United States have developed illnesses thought to have been caused by S. enteritidis present in raw or undercooked eggs. So the presence of S. typhimurium in an egg-related contamination case is a break with the established pattern.
There are more than 2,100 different serotypes of salmonella, and S. typhimurium has been the most common in California and nationally, said Ben Werner, the infectious disease branch's chief epidemiologist.
Even so, S. enteritidis, in part through its contamination of eggs, has become the leading cause of illness from this bacterial group in mid-Atlantic states, Werner said. To date, California health officials have not identified any outbreaks of S. enteritidis traceable to raw eggs, he said.
Another noteworthy aspect of the Kern County outbreak is that the woman who made the ice cream was fully versed in proper food preparation techniques and apparently handled and stored the raw eggs correctly.
Although veterinarians have not conclusively determined how eggs are being contaminated, the prevailing opinion is that the bacteria enters the yolk well before the shell is formed.
"The possibility that eggs may become intrinsically contaminated by S. enteritidis (and other serotypes of salmonella) even before the calcium shell is formed merits attention by all," the report stated.
Most troubling for consumers, Werner said, is that there are no tell-tale signs of bacteria's presence in eggs.
"The eggs can get contaminated in the chicken's ovum or ova duct before the shell is laid down. You may see a healthy looking shell--clean, no cracks, no odor--but the egg can still be contaminated from the inside out. This is a whole new concept," Werner said.
As is the case with other raw animal products, he said that there is an attendant risk in eating eggs in an uncooked state.
Egg Precautions--In light of the most recent contamination incident, the California Department of Health Services issued several recommendations for proper handling and preparation of eggs.
--Store raw eggs in the refrigerator.
--Wash hands before and after handling eggs.
--Cracked or broken eggs should not be used.
--Cook all eggs. An egg is properly heated, or pasteurized, if the white solidifies. Be wary of those dishes, particularly recipes made in the home, that call for raw eggs, such as eggnog, mayonnaise, hollandaise sauce and Caesar salad. (Commercial eggnog and mayonnaise are not affected by the advisory because they contain pasteurized eggs.)
--Egg dishes should be consumed as soon as possible after cooking. If not, refrigerate immediately.
--Blenders that contained raw egg ingredients should be routinely disassembled and disinfected before reuse.