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 Epidemiological Investigation

Since 1946, CDC has used a mechanism called EPI-AID to provide rapid epidemiological response to investigate potential threats to public health. The objectives of EPI-AID #2001-13 included the following:

  1. To quickly determine if FDA AERs were consistent with allergic reactions to food;
  2. To obtain serum samples from individuals in this study who met the case definition for allergic reactions after eating corn-containing food (for possible future serologic testing);
  3. To determine if development of a Cry9c-specific serologic test was warranted.

FDA personnel performed an initial triage of all AERs received since July 1, 2000, selecting those that included consumption of corn products. FDA provided blinded copies of these reports to CDC for review. CDC reviewed the AERs and developed a working case definition for further investigation.

A case was defined as a report forwarded to CDC concerning human consumption of a corn product occurring between July 1 and November 30, 2000, that manifested as follows:

  • A suspected anaphylactic reaction (e.g., dizziness, weakness, or loss of consciousness) that occurred within 1 hour of product consumption, or
  • Any of the following dermatological or oropharyngeal symptoms (hives, rash, pruritis, oropharyngeal tingling or swelling) that occurred within 12 hours of product consumption, or
  • Any of the following gastrointestinal symptoms (vomiting, diarrhea, abdominal cramping) that occurred within 12 hours of product consumption and that involved only one individual among meal companions, and
  • These symptoms not explained by a pre-existing medical condition

FDA requested permission from all reporting individuals to release their identifying information so that CDC could directly contact individuals who had filed AERs. CDC interviewed individuals, either by phone or in person, using a questionnaire that incorporated a validated food allergy survey. CDC also invited each person to provide a blood sample that was to be banked pending the outcome of the CDC investigation and in anticipation of developing a Cry9c-specific serologic test. CDC obtained informed consent from each individual (see Appendix A).

CDC received AERs from FDA involving 51 individuals. Of the 51 individuals who experienced adverse health effects, 23 did not meet the CDC case definition for the following reasons: four experienced symptoms other than those included in the case definition; five had symptoms that did not occur within the established time frame following product consumption; two had symptoms that were attributed to a previously diagnosed illness; and 12 had meal companions who also experienced gastrointestinal symptoms, suggesting infectious causes of foodborne illness.

Of the 28 individuals meeting the case definition, 25 gave FDA permission to release identifying information to CDC; however, one individual who gave permission to be contacted never responded when contact was attempted. CDC completed interviews with 24 of the people who filed AERs and who also met the CDC case definition. These 24 case subjects ranged in age from 5 years to 74 years, with a mean age of 36 years; 13 cases were male and 11 were female. They resided in 15 states (California, Florida, Georgia, Illinois, Kansas, Maryland, Massachusetts, Missouri, New Jersey, North Carolina, Ohio, Texas, Virginia, Washington, and Wisconsin), the District of Columbia, and the Commonwealth of Puerto Rico (see Figure 1 [opens in new window]). No more than 2 people were from the same state or territory. Seventeen of the people who completed questionnaires also provided serum samples.

For 10 of the 24 case subjects, symptom onset was rapid (within 1 hour), and most people reported multiple symptoms. One individual reported loss of consciousness, and two others reported weakness or dizziness, within 1 hour of product consumption. Nineteen individuals sought medical care, and 19 of the 24 case subjects were either self- or physician-treated for allergic reaction. Two people were hospitalized. Case individuals reported having eaten several different corn products from a variety of manufacturers, including corn taco shells, corn tortillas, corn chips, corn cereal, wheat flour tortillas, black beans and rice, and breaded chicken nuggets. (The last three foods are not technically considered corn products, but each listed corn as an ingredient).

CDC presented preliminary results of the epidemiologic field investigation to an EPA scientific advisory panel (SAP) on November 28, 2000. The preliminary findings suggested the utility of developing an enzyme-linked immunosorbent assay (ELISA) to further assess the relation between allergic manifestations and the Cry9c protein. SAP endorsed this recommendation, and CDC began to develop a research protocol to assess the case serum samples as well as comparison serum samples.

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