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Epidemiologic Notes and Reports Multistate Outbreak of Viral Gastroenteritis Associated with Consumption of Oysters -- Apalachicola Bay, Florida, December 1994- January 1995

On January 3, 1995, the Florida Department of Health and Rehabilitative Services (HRS) was notified of an outbreak of acute gastroenteritis associated with eating oysters. The subsequent investigation by HRS has identified 34 separate clusters of cases, many of which were associated with oysters harvested during December 29-31 from 13 Mile Area and Cat Point in Apalachicola Bay. Oysters were shipped to other states, but additional clusters of illness associated with these oysters have been reported only in Georgia. Most of these oysters were served steamed or roasted. This report summarizes the preliminary findings of the ongoing investigation of this outbreak.

On January 4, Apalachicola Bay was closed to harvesting even though levels of fecal coliforms in the water and in the oyster meat were within acceptable limits. The preliminary investigation identified no gross breaches of sanitation; however, during the holiday season, the bay was used heavily by recreational boaters and commercial fishermen. Clusters of cases identified since the bay was closed prompted concern regarding the continued marketing of these oysters as unshelled and as shucked product both in Florida and other states.

Following the detection of cases associated with oysters from Apalachicola Bay, enhanced surveillance detected three additional clusters of cases in Florida and two in Texas initially linked to oysters harvested in Galveston Bay. As a result, on January 13, Galveston Bay was closed to harvesting.

Norwalk-like viruses have been detected by electronmicroscopy in stool specimens from seven of 11 persons who ate oysters from Apalachicola Bay. Reported by: C Aristeguieta, MD, Dept of Family Medicine, Univ of Miami; I Koenders, Districts 1 and 2 Health Office, Tallahassee; D Windham, Districts 3 and 13 Health Office, Ocala; K Ward, MSEH, Districts 4 and 12 Health Office, Daytona Beach; E Gregos, Districts 5 and 6 Health Office, Tampa; L Gorospe, E Ngo-Seidel, MD, Nassau County Public Health Unit, Fernandina Beach; J Walker, MD, District 4 Health Office, Jacksonville; WG Hlady, MD, R Hammond, PhD, RS Hopkins, MD, State Epidemiologist, Florida Dept of Health and Rehabilitative Svcs. DM Simpson, MD, State Epidemiologist, Texas Dept of Health. Viral Gastroenteritis Section, Respiratory and Enteric Viruses Br, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases; Div of Field Epidemiology, Epidemiology Program Office, CDC.

Editorial Note

Editorial Note: Outbreaks of oyster-associated gastroenteritis affect substantially more persons than those identified in the few documented sentinel clusters (1-3). An important feature of these outbreaks is the inherent delays in removing contaminated oysters from the market. Although oyster tags permit traceback to the general harvest areas, they are not sufficiently detailed to allow recall of oysters from a specific site, and they can be lost when oysters are shucked. In this outbreak, the continued occurrence of cases 1 week after the bay was closed and the product was recalled suggests that the contaminated product was still available to consumers. Cooking (i.e., steaming and roasting) did not always render the oysters noninfectious. In addition, enhanced surveillance in Florida prompted by the investigation led to the closing of an oyster bed in Texas. The observation that both the quality of water in the Florida beds and the meat in the implicated oysters met national standards underscores the inherent limitations of the existing methods and the urgent need for improved indicators of viral contamination. In the absence of such indicators, it is difficult to determine when a bed can be safely reopened.

The findings in this investigation indicate the outbreak resulted from consumption of oysters contaminated with Norwalk-like virus. In a previous oyster-associated Norwalk virus outbreak, identification of the identical sequence of the virus genome in specimens from patients in five states established a clear link between those cases and the oysters from one harvest site (1,2). For the outbreaks described in this report, molecular analysis of fecal specimens will be required to determine the number of linked outbreaks and help assess the usefulness of the specific control measures (4,5). However, the preliminary findings suggest that Apalachicola Bay oysters may have become contaminated by sewage dumped overboard by recreational and commercial boaters. Long-term solutions to eliminate fecal contamination of oyster beds will require either that boaters not be permitted to dump sewage overboard or that beds used for harvesting be limited to those in pristine waters. Improved methods to detect virus in these oysters are needed to understand the extent of the contamination and to strengthen prevention efforts and enforcement.


  1. Kohn MA, Farley TA, Ando T, et al. A large outbreak of Norwalk virus gastroenteritis associated with eating raw oysters: implications for maintaining safe oyster beds. JAMA 1995 (in press).

  2. Dowell SF, Groves C, Kirkland KB, et al. A multistate outbreak of oyster-associated gastroenteritis: implications for interstate tracing of contaminated shellfish. J Infect Dis 1994 (in press).

  3. CDC. Viral gastroenteritis associated with consumption of raw oysters -- Florida, 1993. MMWR 1994;43:446-9.

  4. Ando T, Monroe SS, Gentsch JR, Jin Q, Lewis DC, Glass RI. Detection and differentiation of antigenically distinct small round-structured viruses (Norwalk-like viruses) by reverse transcription-PCR and Southern hybridization. J Clin Microbiol 1995;33:64-71.

  5. Lew JF, LeBaron CW, Glass RI, et al. Recommendations for collection of laboratory specimens associated with outbreaks of gastroenteritis. MMWR 1990;39(no. RR-14).

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