Vol. 10 No. 2 June 1990


Table of Contents

Page No.

I. Foodborne Disease Outbreaks, 5-Year Summary, 1983-1987
II. Pesticide Residues in Food in 1988
III. Pesticides and Food Safety: Perception vs.Reality
IV. Malathion: Act II
V. Cancer Classifications for Malathion and PCP
VI. Mass Sociogenic Illness in a Day-Care Center -- Florida
VII. Urban and Agricultural Pesticide Use: How Do They Compare?
VIII. Results of Lead Test Field Trials


This spring has been busy for all of us in Extension trying to continue to deliver effective programs with dwindling resources. Food safety is one issue that attracted a lot of time and resources during the past year. In putting together this newsletter it became apparent that we had scavenged enough material for two, and I found that about half of the articles were related to food safety, so this issue will contain those articles. The next issue, which will follow soon, will present a potpourri of information on many other interesting articlesincluding an update on the Eosinophilia-Myalgia Syndrome, dermatitis caused by moths, malaria in San Diego County, and an answer to the age-old question, "Should you jog in the smog?" Stay tuned.

I. Foodborne Disease Outbreaks, 5-Year Summary, 1983-1987


This report summarizes data from foodborne disease outbreaks reported to CDC (Centers for Disease Control) from 1983 through 1987. With a few exceptions, an outbreak is defined as an incident in which two or more persons experience a similarillness and food is implicated. During this period, 2,397 outbre aks of foodborne disease were reported, representing 91,678 cases. Among outbreaks in which the etiology was determined, bacterial pathogens caused the largest number of outbreaks (66%) and cases (92%)*. Chemical agents caused 26% of outbreaks and 2% of cases. (See the discussion below to see which chemical agents were measured.) Parasites caused 4% of outbreaks and <1% of cases, and viruses caused 5% of outbreaks and 5% of cases. The discrepancies between the number of outbreaks and the number of cases attributed to each etiologic agent emphasizes the importance of evaluating both numbers before drawing conclusions. The etiologic agent was not determined in 62% of outbreaks, reflecting the need for improved investigative skills. The number of outbreaks reported by this surveillance system is only a small fraction of the true number that occur. The likelihood of an outbreak's being reported depends on many factors, such as ease of recognition and ease of laboratory confirmation. Sporadic foodborne illness is far more common and is not includedin this report.

* (an outbreak may involve numerous cases, so the human impact is best represented by the number of cases)


Salmonella accounted for 57% of the bacterial disease outbreaks for the 5-year period and was the most frequently reported bacterial pathogen for each year. Fish poisoning due to ciguatoxin and scombrotoxin accounted for 73% of the outbreaks due to chemical agents (The chemical agents studied do not even include pesticides as a separate category, but includes ciguatoxin, heavy metals, monosodium glutamate, mushrooms, scombrotoxin, and other chemicals). T. spiralis caused all parasitic disease outbreaks for 3 of the 5 years; three Giardia outbreaks occurred during the other 2 years. Hepatitis A caused 71% of the outbreaks due to viruses. The low number of reported outbreaks due to Norwalk agent and other viruses reflects the limitations of current laboratory techniques for detecting these infections.

Inconsistencies in reporting can be seen by examining the distribution of outbreaks by state. A few states, such as New York, California, Washington, and Hawaii, account for a disproportionate number of the outbreaks. Although these states could have a higher rate of foodborne disease, these figures more likely represent differences in degree of surveillance activity. Variability in reporting can also be seen when the frequencies of different pathogens are studied. Outbreaks due to C. botulinum were reported more commonly than those due to Campylobacter, a finding that indicates only that botulism is reported more comprehensively than some other illnesses.

For each year from 1983-1987, the most commonly reported food-preparation practice that contributed to foodborne disease was improper storage or holding temperature, followed by poor personal hygiene of the food handler. Food obtained from an unsafe source was the least commonly reported factor for all 5 years. Inadequate cooking and contaminated equipment each ranked third or fourth in each of the 5 years. In most outbreaks caused by bacterial pathogens, the food was stored at improper holding temperatures. In outbreaks of trichinosis, the food was usually inadequately cooked. In outbreaks of ciguatera and mushroom poisoning, the food itself was unsafe, and illness was not related to improper handling or preparation..

Reference: MMWR, Vol. 39, No. SS-1, March 1990.

II. Pesticide Residues in Food in 1988

Fewer pesticide residues are being found in fruits, vegetables and other foods tested by the Food and Drug Administration (FDA). This is important news because it undercuts the efforts of the more extreme environmental and consumer groups to picture a food supply tainted with chemicals. If there's nothing there, there's not much to complain about.

The figures for 1989 are not in yet, but the results for 1988 look good. FDA has increased its testing to include more samples of domestic and imported foods. In 1988, the agency found that 62 percent of the vegetables and 55 percent of the fruit tested had no detectable residues. Residues within the legal limits were found on 44 percent of the fruits and 33 percent of the vegetables tested. Less than 2 percent of fruits and 5.6 percent of vegetables had violative residues. These figures include both imported and domestic produce.

The FDA sampled 14,200 fruits and vegetables and tested for more than 250 pesticides down to levels of 10 parts per billion. For all foods tested in 1988, 61 percent showed no residues, compared with 57 percent in 1987.

On imports, Mexican produce was tested the most, with 4,385 samples taken. The Dominican Republic had 901 samples tested and Chile had 638. FDA tested foods from 89 countries. One continuing problem with imported produce is the detection of pesticides for which no tolerances have been set in the U.S. Such pesticide residues were found on 6 percent of imported fruits and vegetables.

Reference: The Grower, via Pesticide Digest, University of Georgia, as cited in the Kansas Pesticide Newsletter, Volume 13, No. 3, March 14, 1990.

III. Pesticides and Food Safety: Perception vs. Reality

Much of the public's concern about food safety is basically a clash between public perception and scientific fact. It's easy for that to happen, especially when the U.S. scientific literacy rate continues to average only 3 to 4 percent.

Most instances of public information and concern originate from news media reports. They almost always pertain to the presence of a pesticide residue found in a food. The message the reader or viewer comes away with is that presence equals serious danger. In effect, the perception created is that all pesticides are "dangerous."

The largest potential sources of harm in foods are by far, first, microbiological contamination and, next, nutritional imbalance. The risk from environmental contaminants is 1,000 times less, and the risk from pesticide residues is 100 times smaller again.

Food is very safe when pesticides have been applied properly, in accordance with label instruction. Farmers and applicators cannot legally use any agricultural chemical on any crop and cannot use dosages higher than those prescribed in label instructions.

There are many data that show that the nation's food supply is very safe and becoming safer. Continuing public concerns will doubtless move regulatory agencies to take additional steps. In the end, the result will be additional verification which will help bring public perception more into conformance with scientific reality. Meanwhile, the American Council on Science and Health sees no reason why consumers need to be concerned about health hazards from properly applied pesticides.

Public health has continued to improve throughout the 20th century. There are less infectious diseases, poisoning, and accidents except for manmade health problems caused by smoking, alcohol and guns in the U.S.

Reference: Dr. James H. Steele, USAHA meeting, 1989 as cited in Veterinary News, February 1990.

IV. Malathion: Act II
Carl Winter

In response to public concerns about the safety of malathion used in recent Medfly eradication programs, Carl Winter prepared a document and distributed it to the county offices in the affected area. A few excerpts are included below. A complete copy can be obtained by contacting Carl at Riverside or the Davis Extension Toxicology office. Those of you who were on board in 1982 may find this update on malathion hazards of interest.

Following an extensive review of scientific and regulatory literature concerning malathion, I am not aware of any documented scientific evidence suggesting that the spraying of malathion in urban areas to control the Medfly should pose any significant health risks to residents (including children, the elderly, pregnant women, asthmatics, etc.) in the spray areas.

This conclusion is based upon the fact that more is known about the toxicology of malathion than virtually any other pesticide and that significant data concerning the effects of malathion on human populations is available. Such data includes epidemiological and clinical studies in urban areas following previous malathion spray programs, including the 1981 Medfly eradication project in northern California, as well as clinical findings from suicide attempts, studies of occupational exposure to malathion, and an older study in which human volunteers were administered daily doses of malathion for periods of several weeks.

It is important that consideration be given to the basic principle of toxicology that states that "the dose makes the poison." While several scientific studies performed using laboratory animals demonstrate that large doses of malathion, often administered continuously for long time periods, can cause effects such as neurotoxicity and decreased body weights, such effects are not expected to occur in human populations due to the small amounts of malathion (2.8 ounces of malathion per acre) applied in the aerial spray program. Common backyard gardeners would expect to receive significantly greater exposures from applications to a single tree of commercially available malathion formulations.

In summary, while many concerns have been raised concerning the safety of malathion used in the aerial spraying to control the Medfly, I am confident that the low levels of human exposure to malathion anticipated from the spraying do not pose significant health threats to the population, including children, the elderly, pregnant women, or those suffering from asthma. This opinion is based upon an extensive review of scientific and regulatory data on malathion and consideration of opposing arguments.

V. Cancer Classifications for Malathion and PCP

Malathion has been classified as a "D" oncogen by Peer Review Committee, Health Effects Division, OPP, EPA. It is the agency's interim position that there is no evidence of carcinogenicity for the pesticide, but that more data are being requested, an EPA official said.

For those of you unfamiliar with the EPA classification for oncogens, this is what they mean: Category A - Human Carcinogen (Human data available); Category B - Probable Human Carcinogen, category B1 means there is some limited human evidence, category B2 means there is sufficient animal evidence; Category C - Possible Human Carcinogen (animal data only, but not clear-cut); Category D - Not Classifiable as to Human Carcinogenicity (animal data even less clear-cut, and even suspect); Category E - Evidence of Non-carcinogenicity (almost impossible to prove since negative animal tests are not evidence of non-carcinogenicity, they are just negative tests).

The EPA Science Advisory Board's (SAB) Environmental Health Committee, agreeing with EPA, has recommended that pentachlorophenol be classified as a probable human carcinogen in Group B2 but, in doing so, voiced reservations about the lack of available data.

"EPA needs to fast-track a rat study on penta;...I am concerned that we do not have two species with the same lesion; based on that, the 'C' category was considered," said Dr. Michael Gallo, Biology Department, Woods Hole Oceanographic Institution, Mass.

Reference: P&TCN, Vol. 18, No. 16, as cited in Kansas Pesticide Newsletter, Volume 13, No. 3, March 14, 1990.

VI. Mass Sociogenic Illness in a Day-Care Center -- Florida

On July 26, 1989, 63 (42%) of 150 children attending a summer program at a day-care center in Florida experienced a gastrointestinal illness. An epidemiologic investigation by Orange County public health officials and the Florida Department of Health and Rehabilitative Services concluded that this outbreak was the result of mass sociogenic illness (MSI).

Onset of symptoms occurred within 2-40 minutes after lunch and included abdominal cramps (77%), nausea (75%), headache (51%), dizziness (30%), malaise (30%), and sore throat (11%). Vomiting was reported in 67% of children, but no distinction could be made between actual vomiting and spitting out food. The median duration of illness was 1 hour (range: 1-8 hours). Ill children ranged in age from 4 to 14 years (median: 9 years); 47 (75%) were female. Within 1-2 hours after onset, all symptomatic children were evaluated in emergency departments at local hospitals; when the children arrived at the emergency departments, most symptoms were no longer present, and all physical examination findings were normal. More than 90% of the children returned to the center on July 27, and no further episodes occurred.

A prepackaged lunch was served in one large room to the children and consisted of a ham and cheese sandwich, diced pears, chocolate milk, and apple juice. The center's staff reported that the initial case occurred in a 12-year-old girl who complained that her food tasted bad. She subsequently had nausea and vomited. As more children developed similar symptoms, some of the staff suggested to the children that the food may have been contaminated.

Meal samples collected and tested by the Food and Drug Administration did not detect pesticide contamination, staphylococcal toxin, or Bacillus cereus; atomic absorption screening for heavy metals, zinc, and copper was also negative. Review of the food processing, storage, and refrigeration at the manufacturing plant and the day-care center did not identify deficiencies in handling or a source of contamination. The plant that had prepared the prepackaged meal had produced 3600 similar meals served in 68 different sites in central Florida on July 26. No complaints of similar symptoms were reported from the other sites. The investigation did not identify any chemical exposure, air conditioning failure, or unusually stressful situation at the center on July 26.

Editorial Note: In this outbreak, the rapid onset and disappearance of symptoms, the lack of physical findings, the preponderance of cases in females, and the absence of a laboratory-confirmed etiologic agent are consistent with MSI. However, three features of this outbreak distinguish it from the typical presentation of MSI: the young age of patients, the absence of documented hyperventilation, and the high prevalence of vomiting reported.

Usual characteristics: absence of laboratory findings; absence of physical findings; adolescent or preadolescent group; benign morbidity; hyperventilation and syncope (fainting); lack of illness in others sharing environment; "line of sight" transmission; preponderance in females; rapid spread and remission; relapse of illness; stressful situation.

MSI outbreaks often generate substantial anxiety and concern in the community and, as illustrated in this report, may present with an atypical pattern or syndrome. Early statements by local physicians and the media about the likely psychogenic origin of the illness may have contributed to the absence of recurrence in this instance. Timely recognition of the nature of the outbreak and prompt reassurance that the illness is self-limited and not caused by a toxic exposure are important considerations for the effective control and prevention of recurrence.

Reference: MMWR, Vol. 39/No. 18, May 11, 1990.

VII. Urban and Agricultural Pesticide Use: How Do They compare?
M.W. Stimmann

During the discussion following my talk on endangered species at the 1990 American Chemical Society meeting in Boston, a woman from the US EPA stated that home use of pesticides was about ten times the agricultural use in the US.

I asked her for a reference supporting the number, and she remarked that she really didn't have one. I know of no data which gives solid information on the ratio of agricultural to urban pesticide use. I have some thoughts on the subject that I want to share with the readers of this newsletter.

In California, we know that farmers report using about 80 million pounds of active pesticide ingredients each year. The pesticides include insecticides, herbicides, fungicides, miticides and so on. The total does not include many products such as chlorine for disinfectant uses. The 80 million pounds is an underestimation of the actual total, but it makes a convenient value for the following computations.

If the urban use is 10 times agricultural use, the total use in California would be 800 million pounds of active ingredients. Most urban products include only a small percentage of active ingredients, but some (such as sulfur) may be close to 100% active ingredient. I believe 25% active ingredient on average is a conservative estimate. Thus, 800 million pounds of active ingredients times four would be 3,200,000,000 pounds of formulated pesticides used in California's urban areas each year.

There are about 28,000,000 people in California. Thus, if urban use exceeds agricultural use by a factor of 10, as claimed, each person in the state would be using 114 pounds of formulated pesticides each year. A family of four would use 456 pounds of pesticides a year.

A ballpark check on these calculations is possible. In California, we tax all economic poisons (pesticides) to support our pesticide registration and enforcement program. Because of trade secret restrictions, exact numbers on all pesticides are not made public, but the numbers are very dependable and probably very close to the real amounts sold in the state. For the year 1987, 607 million pounds of all pesticides (including water purification chlorine, pool chemicals and household cleansers) were sold in California. Total pesticide sales for the state are only one fifth of the amount the woman from EPA estimated were used in urban settings. Thus, the argument for a ratio of 10 to 1 for urban to agricultural pesticide use hardly seems reasonable.

Of course, my concern is that "statistics" such as the one quoted at the meeting tend to take on a life of their own, and if repeated enough become accepted fact. Hopefully, this brief, back of the envelope calculation will help to dispel this particular myth before it becomes entrenched.

VIII. Results of Lead Test Field Trials
Allison Beale

In March and May, 1990, field trials of a quick lead test modified for our use were run at the Davis Farmer's Market. The trials were advertised by the local press and the second test was filmed by two area TV news teams. A third testing day was held at the Sacramento County CE office on 30 May, 1990. The results of these three tests are shown in figure 1.

Figure 1. Results of Three Lead Test Field Trials.

Country of Origin   Results  
  + - % +
Asia 0 14 0
Mexico 3 9 25
USA 1 32 3
Europe 0 11 0
Other 1 13 7
Total 5 79 6

This test differs from methods currently in use by the California Department of Health Services and the Food and Drug Administration (FDA) primarily in that it is so quick to use. It takes only 20-25 minutes to leach available lead from the material being tested and to determine whether or not lead is present. The test is qualitative and semi-quantitative in that it is accurate down to 2 parts per million, the high end of the maximum allowed in pottery by the FDA.

This test procedure is an adaptation of one used by the FDA. Scott Wetzlich, the Extension Toxicology SRA in my office deserves credit for developing its simplicity and reproducibility. One of the unique pleasures associated with this testing program is that it addresses a real hazard to children and adults, not a perceived one. Future plans for testing include expansion of the pilot trials into major programs for minority populations. Our office at Davis is ready to help anyone who would like to institute a testing program in their county, so please call us if you would like to do so. We will arrange for training and distribution of materials. Allison will be pleased to discuss her experience with the testing program and can be reached at the Sacramento CE Office (916) 366-2013.

Art Craigmill
Extension Toxicologist
U.C. Davis

Carl Winter
Extension Toxicologist
U.C. Riverside

Mike Stimmann
Statewide Pesticide Coordinator
UC Davis

Allison Beale
Environmental Toxicology and Water Advisor