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January 13, 1997

Failure of Cooking to Prevent Shellfish-Associated Viral Gastroenteritis

Author Affiliations

From the Epidemic Intelligence Service, Epidemiology Program Office, Division of Field Epidemiology (Drs McDonnell and Kirkland), and National Center for Infectious Diseases, Division of Viral and Rickettsial Diseases, Viral Gastroenterology Unit (Drs Monroe and Glass), Centers for Disease Control and Prevention, Atlanta Ga; Florida Department of Health and Rehabilitative Services, Epidemiology Program, Tallahassee (Drs Hlady and Hopkins); and Department of Family and Community Medicine, University of Miami, Miami, Fla (Dr Aristeguieta). Dr McDonnell is now with the Division of Nutrition, Centers for Disease Control and Prevention, Atlanta; and Dr Kirkland is now with the Division of Infectious Diseases and International Health, Department of Medicine, Duke University Medical Center, Durham, NC.

Arch Intern Med. 1997;157(1):111-116. doi:10.1001/archinte.1997.00440220117015

Background:  In January 1995, Florida experienced the largest outbreak of oyster-associated gastroenteritis ever reported.

Methods:  We interviewed both the cohort of persons from 38 gatherings where illness was reported and a sample of harvesters and harvest-area residents. Oysters were traced by means of tags and dealer records, and water quality measures in harvest areas were reviewed. We examined stool specimens for small round structured viruses by means of electron microscopy and amplification of RNA by reverse-transcriptase polymerase chain reaction. We also tested serum specimens for antibodies to Norwalk virus.

Results:  Of 223 oyster eaters, 58% (129/223) became ill, compared with 3% (2/76) of non—oyster eaters (relative risk, 22; 95% confidence interval, 5.6-87.0). Most oyster eaters (67% [149/223]) ate only cooked (grilled, stewed, or fried) oysters. Oyster eaters who reported eating only thoroughly cooked oysters were as likely to become ill as those who ate raw oysters (relative risk, 0.68; 95% confidence interval, 0.45-1.0; P=.1). In 29 clusters, implicated oysters were from Apalachicola Bay, Florida. A community outbreak occurred in 2 bayside communities before the oyster harvest, leading to an increase in the reportedly common practice of overboard dumping of feces. Small round structured viruses were identified in the stool specimens of 2 harvest-area residents and 9 persons from 8 clusters. Results of water quality tests for fecal coliforms were within acceptable limits.

Conclusions:  This large outbreak of gastroenteritis associated with oysters may have resulted from overboard dumping of feces during a community outbreak of diarrheal illness. Our findings of acceptable water quality measures for fecal contamination and the lack of appreciable protective effect from cooking leave the consumer with no assurance of safety.Arch Intern Med. 1997;157:111-116