Gastroenteritis Associated with Consumption of Raw Shellfish-Hawaii, 1991

On January 2, 1991, 12 of 24 persons who attended one or more of three New Year's celebrations in Honolulu, Hawaii, had onset of gastrointestinal illness. An investigation by the Epidemiology Branch of the Hawaii Department of Health (HDOH) determined that the only common foods shared by participants were oysters and clams provided by one distributor.

Each of the attendees was interviewed regarding clinical manifestations and food consumption. Twelve persons reported having had diarrhea, vomiting, or abdominal cramps within 24 hours after attending one or more of the gatherings. The most common symptoms reported were diarrhea (75%), nausea (75%), abdominal cramps (67%), myalgias (67%), fever (58%), and vomiting (33%). The median duration of illness was 12-14 hours; no cases associated with secondary transmission were reported.

The only food items common to all three parties were oysters and clams served raw at two of the gatherings and both raw and grilled at the third. Fifteen (94%) of 16 attendees who ate any raw seafood ate both raw clams and oysters. Persons who became ill were more likely to have eaten raw clams (11 of 15 vs. one of nine; odds ratio (OR)=22.0; 95% confidence interval (CI)=1.6-667.1) or raw oysters (11 of 16 vs. one of eight; OR=15.4; 95% CI=1.2-447.7). Illness did not occur in the one attendee who ate only raw oysters or the five attendees who ate only grilled seafood. No other foods or beverages were associated with illness.

The implicated oysters had been harvested at two sites in Virginia, purchased through a Virginia dealer, and passed through two Massachusetts dealers before air-freight shipment to Hawaii. The clams were traced to a Massachusetts dealership that routinely received shellfish from clam diggers based in Rhode Island and Massachusetts. Although the tag on the implicated clams listed the harvest site as Narragansett Bay, Rhode Island, the Massachusetts seafood dealership reported that it had inadvertently mislabeled the tag and that the clams had actually been purchased from a fisherman who had harvested the product from an approved area off the New Bedford, Massachusetts, coast. Further examination of the dealership's records indicated discrepancies between the harvest and shipping dates of the implicated product, and the Division of Food and Drugs of the Massachusetts Department of Public Health could not verify the dealership's claims.

Samples of oysters from the implicated lot were tested for bacterial pathogens by the HDOH. These tests identified 80 colonies of Escherichia coli per 100 g, 230 colonies of Vibrio parahaemolyticus per 100 g, and isolated colonies of V. vulnificus and V. fluvialis. In addition, samples of clams and oysters from the implicated lots were analyzed for five indicators of fecal contamination by the Department of Environmental Sciences and Engineering at the University of North Carolina at Chapel Hill. The results by the most probable number method for clams and oysters, respectively, were 230 and 20 colonies of fecal coliforms per 100 g, 375 and 23 colonies of Clostridium perfringens per 100 g, less than 20 and 20 colonies of E. coli per 100 g, less than 30 and less than 30 colonies of enterococci per 100 g, and 1475 and 250 plaque-forming units of male-specific coliphage per 100 g. Results of electron microscopy and tissue culture for enteroviruses are pending at CDC. At the Massachusetts Department of Public Health, an analysis of clams collected from the implicated dealership, but with different lot numbers from those implicated in the outbreak, detected less than 20 colonies per 100 g of fecal coliforms.

On January 16, 1991, state and territorial health departments were notified of the outbreak in Hawaii and the potential for similar outbreaks in other locations. Reported by: S Higashihara, B Kanenaka, Food and Dairy Section, Hawaii Dept of Health Laboratory; M Ching-Lee, MPH, P Effler, MD, D Akiyama, MPH, M Sugi, MPH, Epidemiology Br, E Pon, MD, State Epidemiologist, Hawaii Dept of Health. K Sharifzadeh, DVM, R Waskiewicz, MS, N Ridley, MS, W Hohmann, W Higson, Div of Food and Drugs, Massachusetts Dept of Public Health. M Sobsey, PhD, D Wait, MS, Univ of North Carolina, Chapel Hill. Shellfish Sanitation Br, Food and Drug Administration. Div of Field Epidemiology, Epidemiology Program Office; Viral Gastroenteritis Unit, Respiratory and Enteric Viruses Br, Div of Viral and Rickettsial Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note:

Raw shellfish have been implicated as a vehicle for transmission of numerous enteric pathogens, including Norwalk virus, calicivirus, small round viruses, hepatitis A virus, and Vibrio, Campylobacter, Salmonella, and Shigella species (1,2). In this outbreak, the short incubation period, short duration of illness, and mild symptoms suggest a viral etiology.

In a 1982 survey in New York, clams or oysters from northeastern coastal waters were implicated in 103 outbreaks of gastroenteritis involving 1017 persons (3). In these outbreaks, steamed as well as raw shellfish were implicated. No bacterial pathogens were isolated, but Norwalk virus was implicated by seroconversion testing in five of seven outbreaks.

In this outbreak in Hawaii, the etiologic agent was not identified. Based on the small number of detected colonies of Vibrio (commonly identified in seawater) and the clinical symptoms, these agents were not considered the cause of the outbreak (4). However, the relatively high levels of C. perfringens and male-specific coliphage detected suggest that the clams had been contaminated with high levels of fecal waste before harvesting. Because the levels of fecal coliforms (230/100 g) and E. coli ( less than 230/100 g) detected in these shellfish met Food and Drug Administration (FDA) shellstock standards, microbiologic examination of shellfish for these traditional indicators may be inadequate to assess the risk for viral contamination, especially in shellfish harvested during winter months from cold marine waters. New, more sensitive diagnostic techniques to detect viral pathogens in shellfish are under development (5,6). Efforts are also in progress to develop improved indicators (e.g., bacteriophages of enteric bacteria) of enteric virus contamination of shellfish and shellfish harvesting waters.

This outbreak illustrates the need for timely reporting of outbreaks of shellfish-related illness to facilitate rapid tracing of sources of contaminated seafood. Although this outbreak occurred in Hawaii, the implicated shellfish were traced to sources on the northeastern U.S. coast. Because clams and oysters from these areas are routinely distributed throughout the United States within days of harvesting, the potential exists for outbreaks of gastroenteritis in multiple locations. However, no other shellfish-related outbreaks associated with these lots of shellfish have been reported to FDA or CDC.

Although the National Shellfish Sanitation Program and related state agencies have promulgated comprehensive guidelines for tagging shellfish and tracing its interstate transportation, this outbreak demonstrates that some shellfish dealers do not adhere to these guidelines. Previous outbreaks of shellfish-associated gastroenteritis have also been associated with inappropriately tagged shellfish (1). Because of the need for more effective control measures to ensure a safe seafood supply, the FDA, through the Interstate Shellfish Sanitation Conference, is developing additional requirements for tagging and product identification.

References

1. Morse DL, Guzewich JJ, Hanrahan JP, et al. Widespread outbreaks of clam- and oyster-associated gastroenteritis: role of Norwalk virus. N Engl J Med 1986;314:678-81.

2. Noble RC. Death on the half-shell: the health hazards of eating shellfish. Perspect Biol Med 1990;33:313-22.

3. Wanke CA, Guerrant RL. Viral hepatitis and gastroenteritis transmitted by shellfish and water. Infect Dis Clin North Am 1987;1:649-64.

4. Lowry PW, McFarland LM, Peltier BH, et al. Vibrio gastroenteritis in Louisiana: a prospective study among attendees of a scientific congress in New Orleans. J Infect Dis 1989;160:978-84.

5. Jiang X, Graham DY, Wang K, Estes MK. Norwalk virus genome cloning and characterization. Science 1990;250:1580-3.

6. CDC. Viral agents of gastroenteritis: public health importance and outbreak management. MMWR 1990;39(no. RR-5).

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