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Epidemiologic Notes and Reports Update: Salmonella enteritidis Infections and Grade A Shell Eggs -- United States, 1989

Salmonella enteritidis (SE) remains an important cause of outbreaks and sporadic cases of gastroenteritis in the United States. This report summarizes three outbreaks in 1989 that were associated with Salmonella-contaminated Grade A eggs.

Suffolk County, New York. An outbreak of gastroenteritis occurred among 21 of 24 persons who attended a baby shower on July 1. Severe diarrhea, vomiting, fever, and cramps occurred a median of 9 hours (range: 5.5-57 hours) after the shower. Twenty ill persons sought medical care, and 18 were hospitalized. One attendee who was 38 weeks pregnant delivered while ill; the infant subsequently developed SE septicemia and required prolonged hospitalization. Additional secondary cases occurred in two household members of primary case-patients. SE was isolated from stool or rectal-swab cultures of all 21 primary and three secondary case-patients.

All 21 ill attendees, but none of the three attendees who remained well, reported eating a homemade baked ziti pasta dish consisting of one raw egg and ricotta cheese combined in a large baking pan with cooked tomato meat sauce and refrigerated overnight. The ziti dish was baked for 30 minutes at 350 F (176.7 C) immediately before serving. Several attendees commented that the center of the ziti was still cold when served. SE was isolated from samples of the leftover baked ziti and from a pool of seven eggs from the original carton. The eggs were supplied by a New Jersey egg producer; SE was isolated from several flocks tested at the farm.

Carbon County, Pennsylvania. The Pennsylvania State Department of Health was notified of gastroenteritis in 12 of 32 persons who attended an office party on August 24. Symptoms included diarrhea (100%), headache (58%), abdominal pain (42%), nausea (42%), fever (25%), and vomiting (17%). The median incubation period was 27.5 hours (range: 7-72 hours). Of three persons who were hospitalized, two recovered. The third person, a 40-year-old previously healthy man, experienced severe diarrhea and high fever, was admitted to an emergency room on the fourth day of illness, and died within 2 hours. Clinical course and autopsy findings were compatible with acute salmonellosis; postmortem blood, urine, and stool cultures yielded SE.

The only food and beverages served at the party were six pies (two fruit-based pies and four egg-based custard pies), coffee, and juice. Illness was associated with consumption of the custard pies (relative risk=8.6; 95% confidence interval=1.3-58.6). All the pies had been prepared August 23 by a commercial bakery and held without refrigeration for approximately 21 hours before consumption. Two other cases of Salmonella (identified as group D, which includes SE) infection were reported in persons who did not attend the office party but who ate custard pie prepared by this bakery on the same day. The source of the eggs is unknown.

Knox County, Tennessee. An outbreak of SE gastroenteritis occurred among persons who patronized a restaurant on April 8. Twenty-seven cases were reported to the county health department; stool cultures from 23 persons all yielded SE. At least 24 ill persons reported onset of fever, abdominal cramps, and diarrhea within 48 hours after eating at the restaurant; 11 were hospitalized. All had eaten either Hollandaise or Bernaise sauce on April 8. Ten meal companions of ill persons were contacted; none had developed illness or had eaten Hollandaise or Bernaise sauce (p less than 0.01). Both sauces were prepared with Grade A extra-large eggs that were heated but not thoroughly cooked. No other food item was consumed by greater than 20% of those who became ill. The eggs were traced to a farm in Indiana. Reported by: L Steinert, D Virgil, Brookhaven Memorial Hospital, Patchogue; E Bellemore, Stonybrook Univ Hospital, Stonybrook; B Williamson, E Dinda, D Harris, MD, D Scheider, L Fanella, V Bogacki, F Liska, Suffolk County Dept of Health Svcs; GS Birkhead, MD, JJ Guze wich, MPH, JK Fudala, SF Kondracki, M Shayegani, PhD, DL Morse, MD, State Epidemiologist, New York State Dept of Health. DT Dennis, MD, B Healey, DR Tavris, MD, State Epidemiologist, Pennsylvania State Dept of Health. M Duffy, MD, Knox County Health Dept; K Drinnen, RH Hutcheson, MD, State Epidemiologist, Tennessee Dept of Health and Environment. Div of Field Svcs, Epidemiology Program Office; Enteric Diseases Br, Div of Bacterial Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Since 1979, isolation rates of SE have increased dramatically in New England and, more recently, in the mid-Atlantic states (Figure 1) (1). As of October 31, 1989, 49 SE outbreaks had been reported for 1989; these outbreaks have been associated with 1628 cases and 13 deaths (including 12 deaths in nursing homes). From 1985 through 1988, state health departments reported 140 SE outbreaks associated with 4976 ill persons (of whom 896 were hospitalized) and 30 deaths (Table 1). Contaminated food was implicated in 89 (64%) outbreaks; Grade A shell eggs were implicated in 65 (73%) of these. From 1985 to 1989, the proportion of outbreaks from outside New England and the mid-Atlantic regions increased from 5% to 43%.

Foods containing a single SE-contaminated egg can cause outbreaks of severe illness (2). Salmonellosis can be especially severe in infants less than 3 months of age, in the elderly, and in persons who are immunocompromised. Most SE-associated deaths occur in nursing home residents, but salmonellosis can be fatal in otherwise healthy hosts when ingested in sufficient doses (3).

Thorough cooking kills Salmonella. Contaminated eggs that are liquid or runny after light cooking can contain Salmonella. When eggs are heavily contaminated, standard cooking methods for many egg-containing foods (including Hollandaise and Bernaise sauces, meringue, and scrambled and soft-boiled eggs) may not kill all Salmonella (4,5). If raw or incompletely cooked eggs are held at room temperature for greater than 2-4 hours, the risk of outbreaks of Salmonella infections may increase because Salmonella can grow to high concentrations under such conditions.

In regions where egg-associated salmonellosis has been identified, the public should be advised to not eat raw or undercooked eggs. In addition, consumers should avoid eating foods that contain raw eggs, such as Caesar salad, homemade eggnog, and homemade mayonnaise. Foods made with pasteurized eggs (e.g., commercial eggnog, ice cream, and mayonnaise) are safe to eat. In hospitals and nursing homes, where high-risk patients may be exposed, the risk for outbreaks can be reduced by use of pasteurized egg products in recipes that require pooled eggs and by proper preparation and storage of foods containing eggs. Bulk-quantity pasteurized egg products are available commercially for use in food-service establishments.

Clinicians and microbiologists are encouraged to report cases of salmonellosis to local and state health departments. Because some strains of SE isolated from patients in the northeast are reported to produce minimal H((2))S, suspect isolates that otherwise resemble Salmonella should not be discarded on this basis alone. To help characterize sporadic cases and to assist in epidemiologic investigations, Salmonella isolates can be serotyped by state public health laboratories. When eggs are implicated, investigation of outbreaks and notification of state agriculture departments and the U.S. Department of Agriculture are crucial in efforts to identify sources of contaminated eggs and to develop and implement control measures.

Information on cooking and handling eggs safely is available from the U.S. Department of Agriculture Meat and Poultry Hotline (800 535-4555) and from county extension home economists.

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;259:2103-7.

  2. CDC. Update: Salmonella enteritidis infections and Grade A shell eggs. MMWR 1988;37:490,495-6.

  3. Taylor DN, Bopp CA, Birkness K, Cohen ML. An outbreak of Salmonella associated with a fatality in a healthy child: a large dose and severe illness. Am J Epidemiol 1984;119:907-12.

  4. Baker RC, Hogarty S, Poon W, et al. Survival of Salmonella typhimurium and Staphylococcus aureus in eggs cooked by different methods. Poultry Sci 1983;62:1211-6.

  5. Humphrey TJ, Greenwood M, Gilbert RJ, Rowe B, Chapman PA. The survival of salmonella in shell eggs cooked under simulated domestic conditions. Epidemiol Infect 1989;103:35-45.

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