Epidemiologic Notes and Reports Outbreak of Viral Gastroenteritis -- Pennsylvania and Delaware

Within 48 hours of the University of Pennsylvania-Cornell University football game in Philadelphia on September 19, 1987, 158 students with symptoms of gastrointestinal illness visited the university health service. Band members from both universities, Cornell football players, and spectators, including visiting students and university staff and faculty, had similar symptoms.

Ninety-nine percent of the 158 students visiting the university health service reported nausea; 75% reported vomiting; 48%, diarrhea; 22%, headache; 17%, fever; 18%, chills; and 14%, myalgia. The mean incubation period was 36 hours; symptoms lasted 12 to 48 hours. Ninety-two percent of the students had purchased soda with ice from the stadium concessionaire.

None of the Pennsylvania football team members were affected until September 24 and 25, when 55 became ill. The Pennsylvania football team had used ice from a different source at the September 19 game. However, during practice on September 23, the team used ice supplied by the distributor that had provided the stadium concessionaire's ice on September 19.

On September 21, a physician notified the Delaware Department of Health and Social Services of another outbreak of gastroenteritis among 750 people who attended a museum fund-raiser in Wilmington, Delaware. Attendees were served food and iced drinks, most of which contained alcohol. The ice was traced to the same manufacturer that had supplied the concessionaire in Philadelphia.

Questionnaires were completed by University of Pennsylvania undergraduates, football players, and band members, and by participants at the Delaware fund-raiser to examine the relationship of food, drink, and ice consumption to the development of gastrointestinal illness. In each study, ice was significantly associated with illness. The attack rate for those consuming ice in the Pennsylvania outbreak was 62%, while 10% of those not consuming ice were ill (relative risk (RR) = 6.03; 95% confidence interval (CI), 4.66-7.50). In the Delaware outbreak, the attack rate was 61% for those consuming ice and 16% for those not consuming ice (RR = 3.65; 95% CI, 1.96-6.77).

The ice was traced to a manufacturer in southeastern Pennsylvania whose wells had been flooded by waters from Conestoga Creek following a torrential rainfall on September 8. Ice produced at this factory following the flood was sold to distributors serving Pennsylvania, Delaware, and New Jersey. Pennsylvania and Delaware health department laboratories found high concentrations of fecal coliforms in both the ice and the well water used to produce the ice. An increase in diarrheal illness was also noted among residents along Conestoga Creek who obtained their drinking water from private wells that were also flooded. No source of fecal contamination of the creek has been identified.

No bacterial pathogens were identified from any of the stool samples, but a 27-nm virus-like particle was identified in a sample from a University of Pennsylvania student. Serologic studies of several affected groups are pending.

At the request of the U.S. Food and Drug Administration, the manufacturer recalled ice produced after the flooding. Based on distribution records and the Pennsylvania attack rate, more than 5,000 people may have become ill from consumption of the 60- 300 tons of ice produced in the week following the flood. Macaroni salad and gelatin prepared with ice from the manufacturer were also recalled. The manufacturer agreed to decontaminate its wells and machinery before resuming production. Reported by: GH Talbot, MD, EA Brown, MD, M Collins, MD, DS Smith, MD, University of Pennsylvania School of Medicine, Philadelphia; RB Hirschhorn, MS, RG Sharrar, MD, D Farris, MD, Philadelphia Dept of Public Health; R David, MD, Acting State Epidemiologist, Pennsylvania Dept of Health. DC Rodeheaver, PR Silverman, DrPH, State Epidemiologist, Delaware Dept of Health and Social Svcs. L Johnson, P Oliver, US Food and Drug Administration. Div of Field Svcs, Epidemiology Program Office; Respiratory and Enterovirus Br, Div of Viral Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Ice has rarely been implicated as a vehicle of infection. Its identification as the source in these outbreaks has raised several concerns. The high attack rates of diarrhea among people who ingested ice with alcoholic or carbonated beverages are striking because each of these beverages should have some disinfectant effect. Furthermore, since ice is not consistently controlled by any state or federal agency, jurisdiction for maintaining the quality of commercially produced ice or for recalling already distributed ice is unclear. Some of the containers of ice involved in the Pennsylvania and Delaware outbreaks did not carry labels identifying the manufacturer, and none were marked with the production date. Consequently, tracing the extent of the outbreak and determining which ice to recall was difficult.

This outbreak was characteristic of diarrheal illness caused by viruses other than rotaviruses (1). There were high rates of nausea, vomiting, and diarrhea; the incidence of fever was low; and incubation periods and lengths of illness were short. Stool samples contained no bacterial agents.

Norwalk agent has been identified as the causative agent in 42% of 74 past U.S. diarrhea outbreaks of nonbacterial origin, on the basis of a fourfold rise in antibody titer (2). Other viral agents identified in U.S. outbreaks include the Snow Mountain and Marin County agents (astrovirus-serotype 5). Viral agents associated with outbreaks in other countries, such as caliciviruses, other astroviruses, and non- group A rotaviruses, have not been known to cause outbreaks of diarrheal illness in the United States, perhaps because of current methods of specimen collection, handling, and processing.

Most stool specimens from field investigations are frozen before examination. The finding of a 27-nm virus-like particle in a freshly collected, refrigerated (+4))oC) stool sample may support recent changes in thinking about collection and storage of such specimens. Although deep freezing (-70))oC) maintains the viability of some viruses, it also causes a loss of definition of their structure (3). Examination of fresh, loose, large-volume, refrigerated specimens may be the key to identifying the causative agent in future investigations. Further laboratory studies are being conducted to characterize and identify the agent involved in these outbreaks.

References

1. Kapikian AZ, Chanock RM. Norwalk group of viruses. In: Fields BN, ed. Virology. New York: Raven Press, 1985:1495-1517. 2. Kaplan JE, Gary GW, Baron RC, et al. Epidemiology of Norwalk

gastroenteritis and the role of Norwalk virus in outbreaks of acute nonbacterial gastroenteritis. Ann Intern Med 1982;96:756-61. 3. Cubitt WD, Blacklow NR, Herrmann JE, Nowak NA, Nakata S, Chiba S.

Antigenic relationships between human caliciviruses and Norwalk virus. J Infect Dis 1987;156:806-14.

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