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Epidemiologic Notes and Reports Aldicarb Food Poisoning from Contaminated Melons -- California

At 4 a.m., July 4, 1985, three adults who ate a solid green watermelon purchased in Oakland, California, had rapid onset of nausea, vomiting, diarrhea, profuse sweating, excessive tearing, muscle fasciculations, and bradycardia. The most severely ill was a 59-year-old woman who had been receiving digoxin and who, on examination, had a heart rate of 32 and 4-second periods of asystole. The treating physician diagnosed cholinesterase-inhibitor poisoning, and the patient responded rapidly to atropine. The California Department of Health Services (CDHS) had been alerted the day before by Oregon State Health Division officials of similar, although milder, clusters of illness in Oregon associated with ingestion of striped watermelons, possibly of California origin. CDHS notified the San Francisco Bay Area Regional Poison Control Center to be alert for watermelon-associated illness. When the attending physician consulted the Poison Control Center, CDHS was alerted to the outbreak in California.

CDHS contacted 10 California poison-control centers, 20 selected emergency rooms, and a county health department and identified 12 additional cases in different areas of the state. Later on July 4, Oregon officials reported that aldicarb sulfoxide (ASO) had been detected in several melons associated with similar illnesses. ASO is the primary toxic metabolite of aldicarb (Temik), a systemic pesticide not registered in the United States for use on watermelons. In the melon associated with the index cases in California, ASO was found at 2.7 parts per million.

At 1 p.m. that same day, CDHS ordered an immediate statewide embargo on watermelon sales and issued state media advisories recommending that persons refrain from eating watermelons. Because watermelons had become so intermingled in the distribution chain, melons harvested in fields thought to be contaminated could not be separated from other melons. Therefore, on July 7, it was decided to destroy all watermelons in the California distribution chain.

Between July 4 and July 8, CDHS developed a case definition (Table 2). All local health departments and poison-control centers in California participated in a surveillance program for acute illnesses related to melon ingestion. In addition to establishing the extent and severity of illnesses that occurred before July 4, surveillance was continued for illnesses related to melons stickered and presumed to be in compliance with a California Department of Food and Agriculture testing program and sold after July 10. Active surveillance continued until August 31 (Figure 1), although case reports were received through September 30. A total of 1,350 cases were reported from all regions of California and were classified as follows: before July 10, 1,005 reports were received--493 (49%) probable cases, 269 (27%) possible cases, and 195 (19%) unlikely cases; for 48 (5%), information was incomplete. For July 10 and after, 345 reports were received--197 (57%) probable cases, 101 (29%) possible cases, and 40 (12%) unlikely cases; for seven (2%), information was incomplete. There were 18 reports with date of illness missing. The majority (61%) were one-person incidents. Approximately 22% of the illnesses were two-person clusters, 10% were three-person clusters, and 3% were four-person clusters. The remainder involved clusters of five, six, nine, and 13 persons.

The most severe signs and symptoms included seizures, loss of consciousness, cardiac arrythmia, hypotension, dehydration, and anaphylaxis. Seventeen persons were hospitalized. Six deaths and two stillbirths following acute illnesses associated with watermelon ingestion were reported; however, none of the deaths were attributed by the coroners to ASO ingestion, and fetal tissues from both stillbirths tested negative for ASO. In a third pregnancy, decreased fetal movement was noted the same day as a watermelon-related illness in the mother. The mother subsequently gave birth to a normal child.

Of 250 laboratory tests on melons for ASO, 10 (4%) were positive. These 10 included one ASO-positive stickered watermelon associated with illness reported after July 10; an additional ASO-positive stickered watermelon was reported from Canada. Neither of these two positive melons could be traced back to specific fields.

In addition to the reports of watermelon-related illness, 77 illnesses associated with about 25 cantaloupes were reported. All cantaloupe specimens tested negative for ASO, and approximately half were screened for other pesticides (carbamates, organophosphates, and chlorinated pesticides) and were negative. Fewer complaints associated with other types of melons were reported. Reported by all California local health departments and poison-control centers, RJ Jackson, MD, JW Stratton, MD, Hazard Evaluation Section, LR Goldman, MD, DF Smith, PhD, EM Pond, PhD, D Epstein, MA, RR Neutra, MD, Epidemiological Studies and Surveillance Section, A Kelter, MD, Office of Environmental Health Hazards Assessment, KW Kizer, MD, California Dept of Health Svcs; Special Studies Br, Div of Environmental Hazards and Health Effects, Center for Environmental Health, CDC.

Editorial Note

Editorial Note:This is the largest recorded North American outbreak of foodborne pesticide illness. In addition to the 692 probable cases reported by California, 10 other jurisdictions in the United States and Canada reported 483 probable or possible cases according to their own case definitions: Alberta (20), Alaska (47), Arizona (one), British Columbia (206), Colorado (one), Hawaii (two), Idaho (80), Nevada (four), Oregon (104), and Washington (18).

Aldicarb is a carbamate insecticide used in citrus groves and potato fields. Unlike organophosphates, which also interfere with cholinesterase activity, inhibition of cholinesterase by carbamates is rapidly reversible.

Aldicarb has the lowest LD((50)) of any pesticide registered in the United States (LD((50((1 mg/kg body weight) (1). Aldicarb sulfoxide has nearly the same LD((50)). It has been associated with at least two deaths among agricultural workers (2,3). It is a highly effective systemic insecticide, readily taken up by the roots and carried into the stem, leaves, and fruit of the plant. Severe and potentially lethal contamination levels can result from intentional or inadvertent misapplication to certain crops, as seen in several prior episodes of foodborne aldicarb poisoning involving cucumbers and mint (4,4). It is not registered for use on melons.

Existing toxicologic data on aldicarb did not predict the severity of the acute illnesses associated with the dose levels found in this outbreak. Animal data do not predict long-term or reproductive effects from aldicarb and its metabolites, and it is not a suspected carcinogen (6). However, few reproductive studies have been conducted at doses that cause maternal toxicity, and, in rats, it has been shown to cause acetyl cholinesterase inhibition in fetal tissues (7).

In the California outbreak, coincidental onset of gastrointestinal illness within 2 hours of eating melon may explain some of the sporadic cases occurring through September. However, the source of illnesses is not clear among those who had illnesses compatible with carbamate poisoning but where laboratory testing of the melons was negative for ASO. Although some of these may have been coincidental, it is possible that the laboratory analyses are too insensitive to detect ASO at levels that can cause human illness. This issue has implications for monitoring pesticide residues in foods and needs further study.


  1. Moses M. Pesticides. In: Rom WM, ed. Environmental and occupational medicine. Boston: Little, Brown and Company, 1983:547-71.

  2. U.S. Environmental Protection Agency. Aldicarb information sheet. July 1985.

  3. Lee MH, Ransdell JF. A farmworker death due to pesticide toxicity: a case report. J Tox and Env Health 1984;14:239-46.

  4. Marshall E. The rise and decline of TemikTM. Science 1985;229:1369-71.

  5. Goes EA, Savage EP, Gibbons G, Aaronson M, Ford SA, Wheeler HW. Suspected foodborne carbamate pesticide intoxications associated with ingestion of hydroponic cucumbers. Am J Epidemiol 1980;111:254-60.

  6. Buell GC. Toxicological properties of aldicarb. Berkeley: California Department of Health Services, 1979; publication no. CA/DOH/AIHL/R-203.

  7. Cambon C, Declume C, Derache R. Effect of the insecticidal carbamate derivatives (carbofuran, pirimicarb, aldicarb) on the activity of acetylcholinesterase in tissues from pregnant rats and fetuses. Toxicol Appl Pharmacol 1979;49:203-8.

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