WTP estimates of the societal costs of U.S. food-borne illness.

(1) The first estimate of costs of food-borne illness, for selected bacterial pathogens, was published in the American Journal of Agricultural Economics in 1989 by Roberts. The human capital method was used to value mortality and the cost of illness method for morbidity. While the USDA's Economic Research Service and the Environmental Protection Agency continue to use various cost of illness methods for morbidity, the Food and Drug Administration uses Quality Adjusted Life Years. Today, all three agencies use the WTP method to value mortality, based on labor market risks.

Previous ERS morbidity estimates use the Cost of Illness method, along with disease outcome trees for each pathogen laboriously built from medical data to indicate the probability of different acute illness and chronic disease outcomes over a lifetime. The limitation, however, was that only a handful of diseases were included in the ERS food-borne illness cost estimates. The WTP approach used in this paper has the benefit of including all acute food-borne illnesses, but excludes costly chronic complications that can last a lifetime, such as kidney failure, paralysis, arthritis, and mental retardation.

(2) Mead et al. (1999) list that 19% of food-borne illnesses are identified by pathogen. This number is based on two multiplication factors. First, FoodNet sites with active pathogen surveillance are only 7.5 % of the U.S. population. Second, most cases with a positive pathogen test were multiplied by 38 to adjust for the other cases where the ill person did not seek medical care, where the physician did not ask for a stool sample, where the test did not give a positive result even though the patient was positive, and where the positive test was reported to the CDC. The 0.04% result of actual, known positive tests is Mead's 0.19, multiplied by the population fraction that FoodNet covers (0.075) and divided by 38.

(3) FoodNet survey instruments for physicians and the general population define an illness as "... [grater than or equal to]3 loose stools in 24 hours with impairment of daily activities or duration of diarrhea of more than a day" (Jones et ai. 2006).

(4) The information problem is illustrated by salmonellosis, an infection with a bacterium called Salmonella. This bacterium lives in the gastrointestinal tracts of mammals, birds, and reptiles. It is one of the most common causes of human food-borne illness and results in diarrhea, fever, and abdominal cramps 12-72 hours after food consumption (CDC 2007). Many different kinds of illnesses can cause diarrhea, fever, or abdominal cramps. Determining that Salmonella is the cause of the illness depends on laboratory tests that identify Salmonella in the stools of an infected person. The diversity of foods contaminated and the delay before illness strikes make linking the pathogen to the food difficult, unless there is a well-documented outbreak where people are surveyed about what they ate in the days before the illness. Human salmonellosis illnesses usually last four to seven days, and most persons recover without treatment. Sometimes the diarrhea is so severe that the patient needs to be hospitalized. In these patients, the Salmonella infection may spread from the intestines to the blood stream, and then to other body sites and can cause death unless the person is treated promptly with antibiotics. The elderly, infants, and those with impaired immune systems are more likely to have a severe illness. (See CDC (2007) for details.)

(5) Another method for forcing linearization is to assume the one-day values are the most accurate and multiply the one-day value by the number of days in each severity category. This method will dramatically increase the estimate above the $1.4 trillion Societal Costs of Food-borne Illness. I also calculate a third sensitivity analysis, based on Hammitt and Haninger's concluding statement: "Our stated-preference estimates suggest that WTP to reduce risk of short-term morbidity from food-borne pathogens is on the order of $10,000 per statistical case avoided for adults and twice as large for children" (2007). This result is $1.2 trillion annually.

Tanya Roberts is Economist with the Economic Research Service, United States Department of Agriculture. I thank James K. Hammitt, Harvard University, and Jason E Shogren, University of Wyoming, for insightful discussions and access to the literature on valuation. David Zorn, Food and Drug Administration, and Chris Dockins and Kelly Maguire, Environmental Protection Agency, provided useful information on valuation methods used for morbidity and mortality in their agencies.

The views expressed in this paper are those of the author and do not reflect the views of the Economic Research Service or the U.S. Department of Agriculture.

This article was presented in a principal paper session at the AAEA annual meeting (Portland, OR, July 2007). The articles in these sessions are not subjected to the journal's standard refereeing process. Table 1. Hammitt and Haninger's Willingness to Pay Values for Safer Food Severity of Symptoms (a) Duration Value per Value per

of Illness Child Case Adult Case (b) Moderate/no medical care 1 day $28,000 $11,100 Moderate/see physician, 3 days $30,400 $11,700

no test Moderate/see physician, 7 days $26,500 $14,400

+test Severe/hospitalized cases 7 days $26,700 $16,100 Source: Hammitt and Haninger (2007). Estimates are median WTP values to avoid morbidity caused by food-borne pathogens. (a) Moderate Symptoms--You will have an upset stomach, fever, and will need to lie down most of the time. You will be tired and will not feel like eating or drinking much. Occasionally, you will have painful cramps in your stomach. In addition, you will have some diarrhea and will need to stay close to a bathroom. While you are sick, you will not be able to go to work or do most of your regular activities. Severe Symptoms--You will have to be admitted to a hospital. You will have painful cramps in your stomach, fever, and will need to spend most of your time lying in bed. You will need to vomit and will have severe diarrhea that will leave you seriously dehydrated. Because you will be unable to eat or drink much, you will need to have intravenous tubes put in your arm to provide nourishment. (b) Adult values are those for the more numerous category of "households without children." Table 2. Illnesses, Hospitalizations, and Deaths in FoodNet, by Age, 2001-2005

0-14 15-69 Case Severity/Age # % # % Illness confirmed by pathogen test 25,821 41% 35,263 55% Cases that require hospitalization 4,828 31% 8,444 55% Food-borne illness caused deaths 36 10% 158 43%

70+ Case Severity/Age # % Total Cases Illness confirmed by pathogen test 2,338 4% 63,422 Cases that require hospitalization 2,148 14% 15,420 Food-borne illness caused deaths 174 47% 368 Note: The illness severity categories are mutually exclusive. Data from FoodNet, Ida Rosenblum, April 2007 email. Table 3. U.S. Societal Annual Costs of Acute Food-Borne Illness Based on Willingness to Pay Values from Hammitt and Haninger (2007) and Viscusi and Aldy (2003)

Adult Cases (a) Severity/Age # $/Case No medical care $35,800,000 $11,100 See physician, no + test $7,600,000 $11,700 See physician, +test $1,175,000 $14,400 Hospitalized $220,000 $16,100 Death $4,680 $7 million Total

Child Cases (0-14) Severity/Age # $/Case No medical care 25,000,000 $28,000 See physician, no + test 5,280,000 $30,400 See physician, +test 816,000 $26,500 Hospitalized 105,000 $26,700 Death 520 $12 million Total

Total Cases/Costs Severity/Age # $/(Billion) No medical care 60,800,000 1,098 See physician, no + test 12,878,489 249 See physician, +test 1,991,311 39 Hospitalized 325,000 6 Death 5,200 34 Total 76 million $1,426 billion (a) Elderly, defined as 70+, are valued with other adults in the morbidity valuations. Elderly are valued separately for deaths, at 70% of the other adult value, or $5 million.