Outbreak of Salmonella enteritidis Associated with Homemade Ice Cream -- Florida, 1993

On September 7, 1993, the Epidemiology Program of the Duval County (Florida) Public Health Unit was notified about an outbreak of acute febrile gastroenteritis among persons who attended a cookout at a psychiatric treatment hospital in Jacksonville, Florida. This report summarizes the outbreak investigation.

On September 6, seven children (age range: 7-9 years) and seven adults (age range: 29-51 years) attended the cookout at the hospital. A case of gastroenteritis was defined as onset of diarrhea, nausea or vomiting, abdominal pain, or fever within 72 hours of attending the cookout. Among the 14 attendees, 12 cases (in five of the children and all seven adults) were identified. The median incubation period was 14 hours (range: 7-21 hours); the mean duration of illness was 18 hours (range: 8-40 hours). Predominant symptoms were diarrhea (93%), nausea or vomiting (86%), abdominal pain (86%), and fever (86%). All ill persons were examined by a physician. Salmonella enteritidis (SE) (phage type 13a) was isolated from stool of three of the seven patients from whom specimens were obtained.

Eleven of the 12 ill persons had eaten homemade ice cream served at the cookout. No other food item was associated with illness. Testing of a sample of ice cream revealed contamination with SE (phage type 13a).

The ice cream was prepared at the hospital on September 6 using a recipe that included six grade A raw eggs. An electric ice cream churn was used to make the ice cream approximately 3 hours before the noon meal. The ice cream had been properly cooled, and no food-handling errors were identified. The person who prepared the ice cream was not ill before preparation; however, she became ill 13 hours after eating the ice cream. Her stool specimen was one of the three stools positive for SE (phage type 13a).

The U.S. Department of Agriculture's (USDA) Animal and Plant Health Inspection Service attempted to trace the implicated eggs back to the farm of origin. The hospital purchased eggs from a distributor in Florida. However, the traceback was terminated because the implicated eggs from the distributor had been purchased from two suppliers -- one of whom bought and mixed eggs from many different sources. Current USDA Salmonella regulations limit testing of flocks to one clearly implicated flock.

Reported by: P Buckner, MPH, D Ferguson, HRS Duval County Public Health Unit, F Anzalone, MD, D Anzalone, DrPH, College of Health, Univ of North Florida, Jacksonville; J Taylor, Office of Lab Svcs, WG Hlady, MD, RS Hopkins, MD, State Epidemiologist, State Health Office, Florida Dept of Health and Rehabilitative Svcs. Foodborne and Diarrheal Diseases Br, Div of Bacterial and Mycotic Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: The outbreak described in this report represents the fourth SE outbreak in Florida since 1985; this outbreak is the first in the state to implicate eggs. In the United States, the number of sporadic and outbreak-associated cases of SE infection has increased substantially since 1985; much of the increase can be attributed to consumption of raw or undercooked eggs (1-3). During 1983-1992, the proportion of reported Salmonella isolates that were SE increased from 8% to 19%. During 1985-1993, a total of 504 SE outbreaks were reported to CDC and resulted in 18,195 cases, 1978 hospitalizations, and 62 deaths (Table_1). Of the 233 outbreaks for which epidemiologic evidence was sufficient to implicate a food vehicle, 193 (83%) were associated with eggs. Of these 193 outbreaks, 14 (7%) were associated with consumption of homemade ice cream. No outbreaks have been associated with pasteurized egg products.

After eggs are identified by public health officials as the cause of an SE outbreak, USDA attempts to trace the implicated eggs back to the farm of origin to conduct serologic and microbiologic assessments of the farm. If SE is detected on the source farm, the eggs are diverted to pasteurization, or the flocks are destroyed. Under current regulations, USDA can pursue the traceback only if one farm is identified as the source. During 1990-1993, the success rate of USDA tracebacks to the source farm declined from 86% (19/22 outbreaks) in 1990 to 17% (3/21 outbreaks) in 1993. The rate declined primarily because eggs increasingly have been marketed in shipments containing eggs from multiple sources.

Although 0.01% of all eggs contain SE and, therefore, pose a risk for infection with SE (4), raw or undercooked eggs are consumed frequently. Based on the Food and Drug Administration (FDA) Food Safety Survey conducted in 1993, 53% of a nationally representative sample of 1620 respondents reported ever eating foods containing raw eggs; of these, 50% had eaten cookie batter, and 36% had eaten ice cream containing raw eggs (S. Fein, FDA, personal communication, September 9, 1994). Many persons may eat raw or undercooked eggs because they are unaware that eggs are a potential source of Salmonella (3) and that certain foods (e.g., homemade ice cream, cookie batter, Caesar salad, and hollandaise sauce) contain raw eggs.

Consumers should be informed that eating undercooked eggs may result in Salmonella infection. In addition, eggs should be refrigerated to prevent proliferation of Salmonella if present and should be cooked thoroughly to kill Salmonella. Because most serious illnesses and deaths associated with salmonellosis occur among the elderly and immunocompromised persons, these persons in particular should not eat foods containing raw or undercooked eggs. Hospitals, nursing homes, and commercial kitchens should use pasteurized egg products for all recipes requiring pooled eggs or raw or undercooked eggs and should refrigerate all eggs and egg products.

References

1. St. Louis ME, Morse DL, Potter ME, et al. The emergence of grade A eggs as a major source of Salmonella enteritidis infections: new implications for the control of salmonellosis. JAMA 1988;259:2103-

3. Mishu B, Koehler J, Lee LA, et al. Outbreaks of Salmonella enteritidis infections in the United States, 1985-1991. J Infect Dis 1994;169:547-52.

4. Hedberg CW, David MJ, White KE, MacDonald KL, Osterholm MT. Role of egg consumption in sporadic Salmonella enteritidis and Salmonella typhimurium infections in Minnesota. J Infect Dis 1993;167:107-11.

5. Mason J, Ebel E. APHIS Salmonella enteritidis Control Program {Abstract}. In: Snoeyenbos GH, ed. Proceedings of the Symposium on the Diagnosis and Control of Salmonella. Richmond, Virginia: US Animal Health Association, 1992:78.

TABLE 1. Number of reported outbreaks, associated cases, hospitalizations, and
deaths caused by Salmonella enteritidis, by year -- United States, 1985-1993
===============================================================================
             No.          No.             No.             No.
Year      outbreaks      cases     hospitalizations     deaths
--------------------------------------------------------------
1985          26         1,166            144              1
1986          48         1,539            131              6
1987          53         2,498            523             15
1988          40         1,010            121              8
1989          77         2,394            175             14
1990          70         2,273            288              4
1991          68         2,346            151              4
1992          59         2,748            229              4
1993          63         2,221            216              6

Total        504        18,195          1,978             62
--------------------------------------------------------------
===============================================================================

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