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Outbreak of Gastrointestinal Illness Associated with Consumption of Seaweed -- Hawaii, 1994

Seaweed is frequently served as a side dish at meals in the Pacific Islands and is a common component in the diet of many persons living in the Pacific Rim. Seaweed is often harvested at beaches, gathered in nearshore waters, or purchased at local markets. It is served either raw or cooked and is commonly prepared with salt and/or other spices and herbs (e.g., chili pepper, ginger, and garlic). Previous reports have documented a toxic illness associated with seaweed harvested in some locations in the Pacific (1,2). This report summarizes the investigation of an outbreak of acute gastrointestinal illness associated with consumption of seaweed during a picnic in Hawaii in September 1994.

On September 9, 1994, a 60-year-old woman contacted the Maui County Health Department (MCHD) to report a burning sensation in her mouth and throat that occurred 15 minutes after she tasted a seaweed ("ogo") preparation. The woman had received the seaweed from a friend on September 1 and had prepared the seaweed on September 2 by washing it, then boiling it in water for 1-2 minutes, and finally mixing it with vinegar, sugar, soy sauce, and sliced cucumbers. The seaweed mixture then was refrigerated. Approximately 4 hours after preparation, she tasted the mixture and, 15 minutes later, had onset of a sore throat and mouth, and headache. She was examined by a physician on September 3; a throat culture obtained during the visit was negative.

MCHD determined that the seaweed from which the woman's portion had come was to be served at a picnic on September 5 on the island of Hawaii. When contacted by the Hawaii County Health Department, some picnic attendees reported having had onset of nausea and diarrhea soon after eating at the picnic.

To assess the role of different foods as risk factors for illness, the Hawaii Department of Health (HDOH) surveyed all 13 picnic attendees. A questionnaire was administered by telephone to the attendees regarding menu items consumed, onset of illness, and symptoms. Menu items included poi, two types of fish (mamo and awe), beef stew, ogo (seaweed), salmon salad, steak, rice, tuna salad, chips, crackers, beer, soda, and water. A case was defined as onset of a burning sensation in the mouth or throat or two or more of the following symptoms: vomiting, diarrhea, nausea, or lethargy within 2 hours after eating food items from the picnic.

The seaweed had been prepared on September 4 by washing, removing debris, and cooking in boiling water. It was then mixed with codfish, vinegar, onion, soy sauce, and chili peppers. The woman who had prepared the seaweed and her husband had tasted it soon after preparation, and both noted a burning sensation in their throats that lasted for 4 hours. They attributed the burning sensation to an excessive amount of chili peppers. Before preparation, the seaweed had been stored in previously unused plastic bags and refrigerated.

Of the 13 persons who attended the picnic, eight were aged greater than or equal to 18 years. Illness in seven (54%) attendees met the case definition, and onset occurred 15-90 minutes after eating the meal. All seven ill persons were adults, and five were males. Symptoms included diarrhea (71%), nausea (71%), vomiting (60%), and a burning sensation (57%), and the mean duration of gastrointestinal symptoms was 22 hours. None of the ill persons were examined by a physician.

The only foods statistically associated with risk for illness were seaweed (illness in seven of seven who consumed versus none of six who did not {relative risk (RR)= undefined}) and salmon salad (RR=undefined). Two of the seven persons who had consumed seaweed had eaten less than one serving (i.e., one serving spoon) and experienced only a burning sensation in the mouth and throat; in comparison, the five persons who ate one or more servings experienced gastrointestinal illness.

A leftover sample of the seaweed served at the picnic and another sample harvested from the same site were examined at the University of Hawaii for species identification and toxicity studies. The seaweed was identified as Gracilaria coronopifolia. It was rinsed thoroughly with fresh water and extracted with acetone. The toxicity of the crude extract was assessed by intraperitoneal injection into mice; the mice were observed for symptoms of toxicity. Manifestations of toxicity in the mice included diarrhea at lower dosages and death within 15 minutes at the most concentrated dosages. The compound that induced the most extreme signs of toxicity in the mice was isolated using high-performance liquid chromatography; however, the isolate was not identified.

Bacterial organisms were identified microscopically both on the surface and in the seaweed. These bacteria were cultured or isolated using 2% NaCl Heart Infusion Agar (DIFCO, * Detroit, Michigan). Colonies of two different species of Pseudomonas and Vibrio grew on the culture media. Each culture was then extracted, and the extracted fraction was subjected to the mouse-toxicity test. Mice injected with the extracted fraction from these bacteria exhibited transient weakness but no other signs of toxicity.

The seaweed had been harvested from a site in a bay on a northeast-facing shore in Maui County in water at a depth of 3-5 feet. Two fresh-water streams flow into the bay, and discharge from storm drains pours into one of the streams. In addition, the tides carry tree branches and other debris into the bay. The State Wastewater Management Division of the Hawaii Department of Health collects water samples from this area on a monthly basis but had not documented increased levels of fecal coliforms or any other potential pollutants during the period before the seaweed was harvested. There was no evidence the seaweed had been exposed to pesticides.

HDOH has notified physicians throughout the state about the potential for seaweed-induced toxicity and has requested that physicians report any cases to HDOH. Seaweed samples will be collected from the same site from which the original samples were obtained for toxin surveillance.

Reported by: M Hanne, H Matsubayashi, R Vogt, MD, State Epidemiologist, C Wakida, Hawaii State Dept of Health; S Hau, State Dept of Land and Natural Resources; H Nagai, Y Hokama, Univ of Hawaii. L Solorzano, Food and Drug Administration. Div of Field Epidemiology, Epidemiology Program Office, CDC.

Editorial Note

Editorial Note: The investigation of this outbreak in Hawaii indicated that consumption of seaweed was associated with acute illness in picnic attendees. In addition to the epidemiologic findings, this conclusion was supported by the isolation of toxin that caused both similar illness and more severe illness in mice. The toxin most likely was elaborated by the seaweed itself or by a coexistent microorganism and probably was heat resistant because both samples of seaweed were boiled before consumption.

Although this outbreak was the first reported episode of seaweed-related illness in Hawaii, this problem has been reported previously in other areas in the Pacific Rim. For example, in 1991, a total of 13 persons became ill, and three of them died after eating seaweed harvested in Guam (3); the seaweed species was identified as Gracilaria tsudai, and manifestations included gastrointestinal illness, fever, wheezing, muscle fasciculations, and hypotension. In 1992, three persons had onset of illness after eating seaweed harvested on a beach in California (4); the seaweed species implicated in that episode was Grasilariopsis lemanaeformis. In 1993, two persons became ill, and one of them died after eating Gracilaria verrucosa seaweed in Japan (1). In the episodes in both Guam and California, the implicated seaweed previously had not been known to develop toxicity.

Although the mechanism of development of toxicity in seaweed has not been clearly determined, findings of previous studies suggest that some species of seaweed may become toxic at the end of their reproductive cycle, and thereby exhibit a seasonal variation in toxin production (2). Other suggested mechanisms are that stress from over-harvesting may cause seaweed to begin elaborating toxin as a method of protection (5) and that environmental changes and increased pollution promote colonization of toxin-producing bacteria.

State and local health departments should inform persons who may eat seaweed that seaweed consumption can be associated with illness and that varieties previously consumed with safety may undergo changes that increase their potential for causing illness. Episodes of seaweed-related illness should be reported promptly to state and local health departments.


  1. Noguchi T, Matsui T, Miyazawa K. Poisoning by the red alga 'Ogonori' (Gracilaria verrucosa) on the Nojima Coast, Yokohama, Kanagawa Prefecture, Japan. Toxicon 1994;32:1533-8.

  2. Yasumoto T. Guam seaweed poisoning: biochemistry of the Grasilaria toxin. Micronesica 1993;26:53-7.

  3. Haddock R. Guam seaweed poisoning: food histories. Micron 1993;26:35-8.

  4. Snyder B. Seaweed suspect in poisoning of Livermore family. Oakland Tribune, Nov 2, 1992: 1(col 1).

  5. Meyer KD, Paul V. Intraplant variation in secondary metabolite concentration in three species of Caulerpa (Chlorophyta: Caulerpales) and its effects on herbivorous fishes. Marine Ecology Progress Series 1992;82:249-57.

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