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Epidemiologic Notes and Reports Update: Salmonella enteritidis Infections and Shell Eggs -- United States, 1990

From January through October 1990, state health departments reported 49 outbreaks of Salmonella enteritidis (SE) in the United States to CDC. This report summarizes three SE outbreaks in 1990 that were associated with shell eggs.

Cook County, Illinois. During October 1-3, at least 435 (23%) of 1900 persons from 30 states who attended a convention banquet in Chicago on September 30 became ill with gastroenteritis and sought medical treatment. Of the 435 ill persons, 147 (34%) were hospitalized. Cultures from 245 persons yielded SE; of five isolates tested for phage type, all were type 8.

The Chicago Department of Health obtained case histories from 92 ill and 55 well persons who attended the banquet; bread pudding with vanilla sauce was implicated as the most likely vehicle for SE. Of the 92 ill persons, 89 (97%) ate the pudding, compared with 24 (44%) of the 55 well persons (odds ratio=38.3; 95% confidence interval (CI)=10.0-173.0); no other foods were associated with illness. The implicated dessert was prepared with grade AA shell eggs and may have been undercooked. In addition, the dessert was left at room temperature for 1-4 hours between cooking and serving.

The eggs were traced to one farm, and SE was isolated from environmental samples of all six chicken houses tested. The sale of fresh eggs from this farm has been restricted, and all eggs from these six houses are being pasteurized.

Fayette County, Kentucky. In August 1990, 42 (65%) of 65 persons became ill with gastroenteritis following a restaurant brunch for a wedding party on August 11. Twenty-three ill persons sought medical care; four were hospitalized. The median incubation period was 28 hours. Stool cultures from seven patients yielded SE; all five SE isolates tested were phage type 8.

Eating eggs benedict with hollandaise sauce was the only food exposure statistically associated with illness. Of 45 persons who ate this food, 38 (84%) became ill, compared with three (23%) of 13 who did not (relative risk=3.7; 95% CI=1.4-10.0).Review of foodhandling practices at the restaurant indicated that eggs used in the hollandaise had been pooled, incompletely cooked, and served greater than 1 hour after preparation.

The eggs were traced to a large midwestern farm. Cultures of environmental specimens from chicken houses on the farm yielded SE, phage type 8. The sale of fresh eggs from this farm has been restricted, and all eggs from chicken houses with positive environmental cultures are being pasteurized.

Cocke County, Tennessee. In late October 1990, six members of two east Tennessee families (A and B) had onset of abdominal cramps and diarrhea; three were febrile, and three required hospitalization. Stool cultures obtained from four of these persons yielded SE. The only exposure common to both families was homemade banana pudding (containing eight shell egg yolks) with a meringue topping (containing eight shell egg whites) prepared by a member of family A on October 25. The pudding was heated for 30 minutes, and the meringue was briefly broiled. All three members of family A ate a portion of the pudding on October 25 and subsequently developed gastrointestinal symptoms (mean incubation period: 30 hours); none required hospitalization.

The pudding was kept refrigerated except for the 1-hour drive to the home of family B. The three members of family B ate the pudding on October 29 and 30; however, their illnesses were more severe than those of persons in family A, their incubation periods were shorter (mean incubation period: 13 hours), and all three required hospitalization. The eggs were traced to a large midwestern farm. An investigation of the farm is pending. Reported by: D Parmer, DVM, E Murray, MD, K Pannarella, MS, F Patch, A Shinall, Chicago Dept of Health; R Martin, DVM, M Swartz, S Bohm, C Langkop, MSPH, BJ Francis, MD, State Epidemiologist, Illinois Dept of Health. E Burden, Louisville-Jefferson County Board of Health; J Sandifer, B Ballard, S Harris, E Beebout, Lexington-Fayette County Health Dept; G Gilliam, D Acker, Woodford County Health Dept; M Russell, P Wright, R Finger, MD, State Epidemiologist, Dept for Health Svcs, Kentucky Cabinet for Human Resources. M Carver, MD, L Kenyon, Cocke County Health Dept; K Drinnen, R Hutcheson, MD, State Epidemiologist, Tennessee Dept of Health and Environment. SE Task Force, US Dept of Agriculture. Div of Field Svcs, Epidemiology Program Office; Enteric Diseases Br, Div of Bacterial and Mycotic Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: From 1976 through 1989, isolation rates of SE increased in general in the United States (Figure 1). In 1989, the 8340 SE isolates reported through the Salmonella Surveillance System represented 20% of all reported Salmonella isolates. SE is the second most frequently reported Salmonella serotype. In 1989, 8549 S. typhimurium isolates were reported; historically, this has been the most frequently reported serotype, accounting for 21% of isolates in 1989.

During 1985-1989, state and territorial health departments reported 244 SE outbreaks, which accounted for 8607 cases of illness, 1094 hospitalizations, and 44 deaths (Table 1). Of the 109 outbreaks in which a food vehicle was identified, 89 (82%) were associated with shell eggs. From January through October in both 1989 and 1990, 49 outbreaks were reported (1). Four (8%) of the 49 outbreaks reported in 1990 occurred in hospitals or nursing homes, compared with 20 (26%) of 77 outbreaks in 1989. The decrease in hospital- and nursing home-associated SE outbreaks may reflect efforts to improve food safety in these settings (in particular, using pasteurized eggs). Although infections with SE first emerged as a public health problem in the New England and mid-Atlantic regions, 22 (45%) of the 49 outbreaks reported in 1990 occurred outside these areas.

In January 1990, five states began electronic transmission of laboratory-based Salmonella surveillance data to CDC using the Public Health Laboratory Information System (PHLIS). This system will replace the current method of transmitting laboratory-based surveillance data by mail, thereby facilitating timely epidemiologic analysis and dissemination of these data. From January through June 1990, these five states reported 1517 isolates of Salmonella through the PHLIS, of which 334 (22%) were SE. During this period in 1989, these states reported 1721 isolates of Salmonella to the Salmonella Surveillance System, of which 439 (26%) were SE. In addition to the outbreak surveillance reports, the preliminary reports of isolates are consistent with minimal changes in the occurrence of SE infection in 1989 and 1990; this pattern could reflect either secular variation in the epidemic or the possible effects of control measures.

Most cases of SE infection occur as sporadic cases or in limited family outbreaks, such as the Tennessee outbreak reported here, and not as part of large common-source outbreaks. Many of these sporadic cases and limited outbreaks may be associated with consumption of contaminated eggs that have been insufficiently cooked to kill Salmonella. Therefore, the occurrence of infections acquired by eating foods prepared in the kitchens of private homes might be reduced by improved education of consumers regarding the risks of eating raw or undercooked eggs and by increased availability of pasteurized eggs. To reduce the risk for SE infection in other settings, such as nursing homes and hospitals, pasteurized egg products should be used in recipes that call for undercooking or pooling of eggs. Similarly, commercial food service establishments can reduce the risk of outbreaks by using pasteurized egg products in such recipes.

An estimated 0.01% (i.e., one in 10,000) of shell eggs contain SE. Consequently, foods containing raw or undercooked eggs (e.g., homemade eggnog, hollandaise sauce, and caesar salad dressing) pose an occasional risk of infection with SE. The likelihood of serious morbidity or death as a result of infection with SE is greatest among very young, elderly, or immunocompromised persons; these persons should be especially careful not to eat foods containing raw or undercooked eggs. Commercial eggnog is made with pasteurized eggs and is safe.

To address the public health problem of SE, two major control measures have recently been implemented. First, on February 16, 1990, the U.S. Department of Agriculture (USDA) began investigating layer flocks of hens that are epidemiologically implicated in outbreaks of human illness (2). Interstate movement of eggs from flocks found to be infected with SE (by culture from chickens' internal organs) is restricted, and eggs are diverted to pasteurization plants or the flock is destroyed. Second, in August 1990, the Food and Drug Administration revised the Model Retail Food Safety codes to include eggs as a potentially hazardous food (3). The revised code recommends that eggs (which had previously been exempt from federal time and temperature regulations that applied to other foods of animal origin) be refrigerated during storage. In addition, food service establishments are advised not to serve raw or undercooked eggs, to substitute pasteurized eggs for pooled eggs when possible, and to serve pooled eggs immediately after cooking.

To help characterize sporadic cases and to assist in epidemiologic investigations, Salmonella isolates should be serotyped by state public health laboratories. Clinicians and microbiologists are encouraged to report cases of Salmonella infection to state and local health departments. When SE outbreaks occur, notification of CDC and the USDA through state health departments will promote identification of contaminated eggs and implementation of control measures.

References

  1. CDC. Update: Salmonella enteritidis infections and grade A shell eggs-- United States, 1989. MMWR 1990;38:877-80.

  2. US Department of Agriculture. Rules and regulations: poultry infected by Salmonella enteritidis. Federal Register 1990;55;5576-84.

  3. Food and Drug Administration. Retail food protection information manual. Rockville, Maryland: US Department of Health and Human Services, Food and Drug Administration, 1990:1-8.

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