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