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Surveillance for Acute Pesticide-Related Illness During the Medfly Eradication Program -- Florida, 1998

The Mediterranean fruit fly (Medfly) (Ceratitis capitata, Wiedemann) is an exotic insect that can damage approximately 250 fruit and vegetable plant species and is a serious threat to domestic agriculture. During the spring and summer of 1998, pesticides were used by federal and state agriculture authorities to eradicate Medfly infestations that had been detected in portions of five Florida counties (Table 1). This report summarizes surveillance data, describes probable and possible cases of illness associated with the eradication effort, and provides recommendations for future Medfly-eradication programs.

The Medfly Eradication Program began on April 4, 1998, with ground applications of malathion/bait* and diazinon, followed by aerial malathion/bait application that began on April 30. All insecticide applications were completed on September 6. The respective county health departments estimated that 132,000 persons resided in the areas treated with these pesticides.

Surveillance for Illness

Reports of potential adverse health effects attributed to the Medfly Eradication Program pesticide applications were solicited by state health and agriculture authorities and collected through telephone hotlines maintained by the Florida Poison Information Network and county health departments. The public was advised of the pesticide use and the hotline number through public meetings hosted by federal and state agriculture department officials, news articles, and radio and television reports. During April 30-September 30, 1998, 230 reports of illness were received from Florida residents and physicians and were investigated by the Florida Department of Health. Reports were classified according to a standard case classification system.** Of the 230 reports, 34 (15%) cases were classified as probable pesticide-related illness based on abnormal medical signs compatible with malathion/bait or diazinon toxicity observed by a licensed health-care professional, and 89 (39%) were classified as possible based on symptoms compatible with malathion/bait or diazinon toxicity reported to health-care providers or a state health authority. Of the remaining 107 (47%), 24 were excluded because of insufficient information, 32 were asymptomatic or had symptoms unrelated to exposure, and 51 were classified as unlikely. No reports were classified as definite cases of pesticide-related illness because this category requires confirmation by laboratory testing of clinical or environmental samples that were not available.

The 123 probable or possible cases represent a crude rate of nine cases per 10,000 residents in the exposed areas. Of the 123, 89 (72%) occurred in females; the median age was 46.5 years (range: 6 months-82 years). Eight reports (7%) involved children aged less than or equal to 5 years, and 20 (16%) involved persons aged greater than or equal to 65 years. Four reports (3%) described persons whose illnesses were considered work-related (i.e., Medfly Eradication Program pesticide applicator, lawn-care worker, health department hotline worker, and hotel worker).

Among the 123 cases, signs and symptoms for 87 (71%) were respiratory (e.g., dyspnea, wheezing, coughing, and upper respiratory tract pain/irritation); 77 (63%) involved the gastrointestinal system (e.g., nausea, vomiting, diarrhea, melena, and abdominal cramping); 74 (60%) involved the neurologic system (e.g., headache, vertigo, ataxia, peripheral paresthesia, disorientation, and confusion); 28 (23%) involved the skin (e.g., erythema [with or without maculopapular rash], pruritis, and burning sensations); and 23 (19%) involved the eyes (e.g., lacrimation, conjunctivitis, blepharitis, and blurred vision)***.

Case Reports

Case 1. A 49-year-old man experienced dyspnea, upper respiratory irritation, and headache after being exposed to aerial malathion/bait applications while working on the roof of his house. His physician diagnosed severe bronchitis and reported that the illness probably resulted from malathion/bait exposure.

Case 2. A 31-year-old man reported a blistering rash over his arms, legs, and neck following an aerial application of malathion/bait. He was exposed to malathion/bait while conducting his lawn maintenance business. He reported that the rash developed where grass trimmings coated with pesticide stuck to his skin. His physician diagnosed allergic contact dermatitis secondary to malathion/bait exposure.

Case 3. A 35-year-old man reported a pruritic rash on exposed skin surfaces. He had covered his pool in accordance with recommendations and was exposed to malathion/bait while removing the cover, which he had folded and carried under his right arm. He was not wearing a shirt, and the rash developed at those points where the pool cover had contacted his arm and torso. His physician diagnosed allergic dermatitis.

Case 4. A 32-year-old woman with a history of asthma complained of multiple symptoms in reaction to ground applications of malathion/bait and diazinon in her neighborhood. Symptoms included nausea, diarrhea, abdominal cramping, cough, upper respiratory irritation, dyspnea, wheezing, headache, and fatigue. Her physician diagnosed acute aggravation of asthma secondary to pesticide exposure from the Medfly Eradication Program.

Reported by: O Shafey, PhD, HJ Sekereke, Jr, PhD, BJ Hughes, PhD, S Heber, DrPH, RG Hunter, PhD, RG Brooks, MD, Florida Dept of Health. Health Studies Br, Div of Environmental Hazards and Health Effects, National Center for Environmental Health; Surveillance Br, Div of Surveillance, Hazard Evaluations, and Field Studies, National Institute for Occupational Safety and Health, CDC.

Editorial Note:

The Environmental Protection Agency (EPA) classifies malathion as an acute toxicity category III compound****, and it is considered safer than many other organophosphates because it is rapidly detoxified by the body. Nevertheless, adverse health effects have been reported by persons exposed to malathion (1). Self-reported health effects previously associated with aerial spraying of malathion/bait include respiratory symptoms (particularly among persons with pre-existing respiratory conditions), gastrointestinal symptoms, neurologic symptoms, contact dermatitis, and conjunctivitis (2-4). These effects may represent irritant or allergic responses to either component of the malathion/bait formulation (5,6). Cholinesterase inhibition (3) or anxiety about aerial malathion/bait application (2,7) also may be responsible for some symptoms.

The findings in this report suggest that for most persons, aerial application of malathion/bait does not pose an acute risk to health; however, at least 123 probable or possible pesticide-related cases of illness were associated with pesticide exposure. Each case-patient had signs and/or symptoms consistent with pesticide exposure, and illness probably resulted from sensitivity to the irritant/allergic effects of malathion/bait. Although ground application of diazinon, another acute toxicity category III organophosphate, was employed in some locations, this agent was considered less likely to be responsible for the observed health effects because it was used in only three counties, was applied focally (without aerial application), and was used in minimal quantities.

The findings in this report are subject to at least three limitations. First, because this was a passive surveillance effort, persons may have become ill who did not seek medical attention or were not reported to the surveillance system. Second, rates of the health outcomes in the exposed population could not be compared with those for the general population because baseline incidence data for many of the effects attributed to the malathion/bait application are not available. Third, the role of cholinesterase inhibition was not determined because blood cholinesterase levels were not obtained.

Certain malathion formulations are registered by EPA for aerial spraying over urban areas in mosquito-control programs. The use of malathion in these programs provides an important public health benefit by controlling mosquitoes that transmit human diseases such as encephalitis, dengue fever, and malaria. Spraying malathion/bait over urban populations for Medfly eradication has generated controversy in part because these applications are directed not at preventing human illness but at eradicating an agricultural pest. Federal law does not permit spraying malathion/bait over urban areas without an emergency EPA exemption*****. To reduce the risk for illness among persons sensitive to the effects of malathion/bait applications, federal and state agricultural authorities are encouraged to pursue and enhance alternative methods for Medfly control. These methods include preventing Medfly importation into the United States, quickly detecting Medfly infestations (e.g. through increased sentinel trapping densities), releasing sterile male Medflies to interrupt the reproductive cycle, and identifying and using safer eradication agents.

During aerial malathion applications for mosquito control and Medfly eradication, the public should be advised to stay indoors and, when appropriate, persons with exposure-related health concerns should seek medical attention. The public also should be provided with an opportunity to ask questions and receive timely responses about the malathion applications (i.e., through telephone hotlines and community meetings). When malathion/bait applications are used for Medfly eradication, additional precautions are recommended, including immediately washing any skin surfaces that come into contact with malathion/bait-contaminated surfaces; providing advance public notification of spray schedules; performing aerial malathion/bait applications when residents are usually indoors (e.g., at night); directing the homeless to shelters; advising highly sensitive persons to leave the area during spraying; and convening a health advisory committee, an action that has been shown to be useful for mitigating risk (7). Medfly Eradication Program workers should be trained in the safe handling of pesticides, and consideration should be given to measuring plasma and red blood cell cholinesterase in these workers before beginning exposure and periodically thereafter (8). Workers should wear the personal protection equipment (PPE) listed on the pesticide label. Supplementary PPE also may be indicated.


  1. Blondell J. Epidemiology of pesticide poisonings in the United States, with special reference to occupational cases. Occup Med 1997;12:209-20.
  2. Kahn E, Berlin M, Deane M, Jackson RJ, Stratton JW. Assessment of acute health effects from the Medfly Eradication Project in Santa Clara County, California. Arch Environ Health 1992; 47:279-84.
  3. Book SA, Jackson RJ, Fan AM, DiBartolomeis MJ, Russell H. Health risk assessment of aerial application of malathion-bait. Berkeley, California: California Department of Health Services, 1991.
  4. Kreutzer R, Harmon L, Hoshiko S. Citizen illness reports following February-May 1994 aerial malathion applications in Corona and Norco, Riverside County, California. Emeryville, California: California Department of Health Services, 1996.
  5. Schanker HM, Rachelefsky G, Siegel S, et al. Immediate and delayed type hypersensitivity to malathion. Ann Allergy 1992;69:526-8.
  6. Sharma VK, Kaur S. Contact sensitization by pesticides in farmers. Contact Dermatitis 1990;23:77-80.
  7. Kahn E, Jackson RJ, Lyman DO, Stratton JW. A crisis of community anxiety and mistrust: the Medfly eradication project in Santa Clara County, California, 1981-82. Am J Public Health 1990;80:1301-4.
  8. California Environmental Protection Agency. Guidelines for physicians who supervise workers exposed to cholinesterase-inhibiting pesticides. 3rd ed. Berkeley, California: California Environmental Protection Agency, 1995.

* Malathion (Fyfanon[Registered] ULV, Cheminova Inc., Wayne, New Jersey) combined with a corn protein bait, Nu-Lure[Registered] (Miller Chemical and Fertilizer Co., Hanover, Pennsylvania) was applied at a rate of 2.4 fluid ounces malathion and 9.6 fluid ounces bait per acre per week. The reportedly nontoxic bait comprises hydrolyzed corn gluten meal and inert ingredients including corn syrup. Backpack sprayers or truck-mounted pressure sprayers were used for ground applications; UH-1 "Huey" helicopters and DC-3 aircraft conducted the aerial applications. (Use of trade names and commercial sources is for identification only and does not imply endorsement by CDC or the U.S. Department of Health and Human Services.)

** CDC's National Institute for Occupational Safety and Health classifies a case of acute pesticide-related illness and injury as being definite, probable, possible, or suspicious as determined by the level of certainty of exposure, whether health effects were observed by a health-care provider, and whether sufficient toxicologic information supports a causal relation between the exposure and the reported health effects. When toxicologic evidence for an exposure-health effect relation is not present, the case is classified as unlikely.

*** Total is 289 cases because some persons experienced signs and symptoms in more than one system.

**** EPA classifies pesticides into one of four acute toxicity categories based on established criteria (40 CFR Part 156). Pesticides with the greatest toxicity are in toxicity category I and those with the least are in category IV.

***** 40 CFR Part 166.

Table 1

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TABLE 1. Number of gallons of malathion applied, number of square miles covered, estimated number of persons exposed, and number of persons adversely affected in the Medfly Eradication Program, by county -- Florida, 1998


Dates of eradication effort

Total malathion volume, excluding bait (gallons)*

Total treatment area (square miles)

Estimated exposed population

Probable and possible cases of illness


April 4-24






April 30-July 13






May 14-June 26






July 9-Sept 6











*In addition, small amounts of diazinon, another organophosphate insecticide, were applied from the ground as a soil drench in Dade (0.04 gallon applied over 0.0001 square mile), Lake (0.3 gallon applied over 0.0007 square mile), and Manatee counties (0.1 gallon applied over 0.0003 square mile).
† No aerial application of malathion/bait; ground application only.
Aerial applications of malathion/bait in Lake County also included small portions of Marion County.

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