Ostrich Fern Poisoning -- New York and Western Canada, 1994

Fiddleheads (crosiers) of the ostrich fern (Matteuccia struthiopteris) are a seasonal delicacy harvested commercially in the northeastern United States and in coastal provinces of Canada. Although some common ferns may be poisonous or carcinogenic, this species has been considered to be nontoxic. However, in May 1994, outbreaks of food poisoning were associated with eating raw or lightly cooked fiddlehead ferns in New York and western Canada. This report summarizes the investigations of these outbreaks. Steuben County, New York

On May 19, 1994, a restaurant in Steuben County, New York, reported to the New York State Department of Health (NYSDOH) gastrointestinal illness among a group of 20 persons who had eaten at the restaurant the preceding night. Patrons complained of nausea, vomiting, and diarrhea shortly after eating, and some attributed their illness to the fiddlehead ferns served with their entree. The restaurant received similar complaints from a group of 22 persons who ate fiddlehead ferns on May 6 but had not previously reported illness.

During May 25-28, NYSDOH conducted a telephone survey of persons who had eaten at the restaurant on days fiddlehead ferns were served (May 6, 7, and 18). A case was defined as vomiting or diarrhea within 12 hours of eating at the restaurant. Of the 56 restaurant patrons who could be contacted, 31 (55%) met the case definition. Of these, 30 (97%) reported diarrhea; 22 (71%), nausea; 10 (32%), vomiting; and eight (26%), abdominal cramps. The mean incubation period was 6.7 hours (range: 0.5-11.5 hours). Symptoms lasted a mean of 1.3 days (range: 3 hours-3 days). Cases occurred among 30 (67%) of 45 persons who ate fiddlehead ferns, compared with one of 11 persons who did not (relative risk {RR}=7.3; 95% confidence interval {CI}=1.1-48.1). The risk for illness was greater for those who ate a full order of ferns (i.e., 8-10 fiddleheads) (RR=8.8; 95% CI=1.4-57.5) than for those who ate a half order or only tasted the ferns (RR=2.2; 95% CI=0.2-20.7). No other restaurant food was associated with illness. A stool sample obtained from one patient was negative for bacterial pathogens.

The ferns had been harvested from two alluvial sites in Chemung County. Both sites abutted corn fields and were approximately three miles from any industry or sewage treatment plants. The harvester delivered the ferns to the restaurant washed, dehusked, and packed in plastic food storage bags. Before being served, the ferns were removed from a refrigerator and sauteed for 2 minutes in butter, garlic, salt, and pepper. No deficiencies in food handling or storage were identified. Cultures of uncooked ferns were negative for Staphylococcus aureus and Bacillus cereus. Standard tests for nitrogen/phosphorous and organochlorine pesticides were negative for chemical contamination.

On May 17, the harvester had sold ferns to a second restaurant in the area; at this restaurant, ferns were boiled for 10 minutes before they were sauteed with butter and lemon. Of six patrons who ate ferns at this restaurant on May 18, none reported illness. Western Canada

On May 17, 1994, three cases of gastrointestinal illness linked to meals served at a restaurant in Banff, Alberta, were reported by the Banff National Park Health Unit to the Health Protection Branch (HPB) of Health Canada (1). A HPB investigation confirmed illness in 17 persons who had eaten at one of eight franchises of the restaurant chain in British Columbia, Alberta, or Saskatchewan during May 10-May 16. The only food eaten by all ill persons was fiddlehead ferns. Fourteen persons had eaten ferns that had been sauteed for 2 minutes with mushrooms, onions, butter, salt, and pepper; three persons had consumed fiddlehead fern soup.

During May 23-June 2, 1994, three persons contacted the HPB complaining of nausea and diarrhea after eating fiddlehead ferns purchased at Vancouver and Victoria markets. One person became ill after eating raw fiddleheads. The other two became ill after eating ferns cooked in a microwave for 7-8 minutes on low power.

On June 10, 1994, a restaurant in British Columbia reported illness among members of three groups who had eaten at the restaurant during May 28-29, 1994. Fiddlehead ferns blanched for 2 minutes in boiling water had been served with all entrees. Of the 21 persons in these groups, illness occurred among 13 (87%) of 15 persons who ate ferns but in no persons who did not eat ferns (RR=undefined; p less than 0.01).

Of the 33 ill persons interviewed, all reported illness within 12 hours of eating ferns (mean: 3.2 hours). Twenty-eight (85%) persons reported diarrhea; 22 (67%), nausea; 11 (33%), abdominal cramps; six (18%), vomiting; and five (15%), headache. In 29 cases, symptoms lasted less than 24 hours. Stool cultures from two ill persons were negative for bacterial pathogens.

A single commercial fern harvester supplied the restaurant chain. Experienced harvesters collected 3-4-inch high ferns during May 1-May 16 on federal land in British Columbia where ferns have been collected for 14 years. The site is approximately 10 miles from any development and industry and had not been sprayed with pesticides or recently flooded. The ferns were inspected to remove debris, packed in open crates, and refrigerated until delivered to purchasers.

Cooked and uncooked samples of ferns from the restaurant and raw ferns collected by the commercial harvester in British Columbia were negative for B. cereus, S. aureus, aerobic and anaerobic spore-forming bacteria, and staphylococcal toxin. There was no evidence of acute illness in mice and rats fed raw and cooked fiddlehead ferns.

Because of concerns that the ferns might contain a heat-labile toxin, Health Canada issued a warning advising that fiddleheads be boiled for 15 minutes or steamed for 10-12 minutes before eating.

Reported by: D Bills, L Arias, P Constantine, T Root, M Shayegani, PhD, K Aldous, G Birkhead, MD, D Morse, MD, State Epidemiologist, New York State Dept of Health; R Mitchell, New York State Biologic Survey. P Morgan, T Morton, F Iverson, PhD, K Catherwood, L Hill, B Long, A McCarville, C Ng, R Smith, K Odermatt, K Reynolds, Health Protection Br, Health Canada; J Raven, Banff National Park Health Unit, Alberta; M Marchenski, Capital Regional District Health Svcs, Victoria, British Columbia; D Armstrong, S Lively, P Brewster, T Mahler, British Columbia Ministry of Health, Canada. Div of Field Epidemiology, Epidemiology Program Office, CDC.

Editorial Note

Editorial Note: The ostrich fern was a spring vegetable for American Indians of eastern North America and became part of the regular diet of settlers to New Brunswick in the late 1700s (2). Until recently, it was consumed primarily in the Maritime Provinces of Canada and in the northeastern United States. The ferns are available commercially either canned or frozen, but since the early 1980s, farmers' markets and supermarket chains have sold fresh ferns in season.

None of the fiddlehead ferns of eastern and central North America previously have been reported to be poisonous (3). Although some ferns may be carcinogenic (4), the ostrich fern has been considered to be safe to eat either raw or cooked (5-9). One field guide indicates that wild greens may have laxative qualities and recommends boiling them and discarding the first water (8).

In both outbreaks described in this report, the specific cause of illness was undetermined. Although the short incubation period suggests poisoning by a preformed toxin, there was no evidence of common bacterial toxins, such as S. aureus or B. cereus. Alternatively, the plants could have been contaminated by an undetected viral agent, although this possibility is unlikely because of the apparent short incubation period. Although the ostrich fern accumulates some heavy metals (9), the symptoms reported in these outbreaks were not characteristic of heavy metal poisoning, and it is unlikely that absorption of heavy metals occurred at two different sites.

Because of the short incubation period and a lack of other plausible causes, the most likely cause of illness in each of these outbreaks was an unidentified toxin. Heating and boiling may either inactivate or leach the toxin from the plant. Fresh fiddlehead ferns only recently have become widely available in restaurants. In addition, many vegetables now are lightly cooked rather than steamed or boiled (10). In both outbreaks, the implicated ferns were either raw or lightly cooked (sauteed, parboiled, and microwaved). In a similar outbreak in British Columbia in 1990, eating lightly cooked fiddleheads was associated with gastrointestinal illness (P. Morgan, Health Canada, personal communication, 1994). Although a toxin has not been identified in the fiddleheads of the ostrich fern, the findings in this report suggest it may be prudent to cook fiddleheads thoroughly (e.g., boiling for 10 minutes) before eating.

References

1. Morgan P, Morton T, Iverson F, et al. Ostrich fern poisoning -- western Canada and New York, 1994. Canada Communicable Disease Report 1994;20 (in press).

2. von Aderkas P. Economic history of ostrich fern, Matteuccia struthiopteris, the edible fiddlehead. Economic Botany 1984;38:14-

4. Peterson LA. Edible wild plants. Boston: Houghton Mifflin Co., 1977.

5. Caldwell ME, Brewer WR. Possible hazards of eating braken fern {Letter}. N Engl J Med 1980;303:164.

6. Newberne PM. Biologic effects of plant toxins and aflatoxins in rats. J Natl Cancer Inst 1976;56:551-5.

7. Brill S, Dean E. Identifying and harvesting edible and medicinal plants. New York: Hearst Books, 1994.

8. Harris B. Eat the weeds. Barre, Massachusetts: Barre Publishers, 1968.

9. Tomikel J. Edible wild plants of Pennsylvania and New York. Pittsburgh: Allegheny Press, 1973.

10. Burns LV, Parker GH. Metal burdens in two species of fiddleheads growing near the ore smelters at Sudbury, Ontario, Canada. Bull Environ Contam Toxicol 1994;40:717-23.

11. Beard J. The New James Beard. New York: Alfred A. Knopf, 1981.

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