How to Read a Worksheet
Reading a worksheet using Shigella as an example
The Shigella worksheet is typical for pathogens that do not involve complications or result in chronic illness. The Excel file for Shigella contains four worksheets: 1) mean cost of illness estimates; 2) low cost of illness estimates; 3) high cost of illness estimates; and 4) numerical assumptions used in each of the three estimates worksheets.
The assumptions spreadsheet contains the number of cases of illness by severity of outcomes and the costs of health outcomes (usually on a per-case basis). The column headings describe specific health outcomes resulting from infection with Shigella. When reading the headings, the severity of health outcomes increases going from the left to right columns. The mildest cases did not seek medical care. Hospitalized cases resulted in either recovery or death. The most severe cases were hospitalized and died.
In the assumptions spreadsheet, the first three rows of data report low, mean and high estimates of the total number of cases and the number of cases for each health outcome by severity in a typical year in the United States. The low, mean, and high case estimates for total cases, hospitalizations and deaths are taken from "Foodborne Illness Acquired in the United States—Major Pathogens" (2011). Estimates for other health outcomes are based on hospitalization records or on synthesis of the scientific literature. "Foodborne Illness Acquired in the United States—Major Pathogens" reports an average (mean estimates) of 131,254 cases of illness from Shigella in a typical year. Of these cases, 120,348 people did not seek medical care, 9,450 saw a physician and recovered without further medical treatment, and 1,456 were hospitalized. Of the 1,456 hospitalized cases, 1,446 recovered and 10 died.
Below the rows with case incidence estimates are assumptions about the costs associated with each health outcome. These are three broad classes of costs: 1) medical treatment costs; 2) lost productivity; and 3) individuals’ willingness to pay (WTP) to prevent the premature mortalities expected in a typical year. For example, of every 10 hospitalized cases of foodborne illness from Shigella, 7 were preceded by a visit to a doctor’s office, at an average cost of $146 per visit; 3 were preceded by an emergency room visit, at an average cost of $701 per visit; and 2 were preceded by an outpatient clinic visit, at an average cost of $806 per visit. Hospitalizations cost an average of $31,8787 per case. Across the population, the total average medical cost per hospitalized case of shigellosis (illness caused by Shigella) is the probability-weighted sum of these per case medical costs, or $32,351.
Some people who were hospitalized for shigellosis were employed and missed work due to their hospitalization. ERS assumes that 43 percent of patients hospitalized for shigellosis were employed, lost 2.22 days of work, and earned an average of $283 per day of work missed. Therefore, the average case of shigellosis resulted in lost earnings of $271 (.43 x 2.22 x $283). More detailed documentation is provided in "Annual Cost of Illness and Quality-Adjusted Life Year Losses in the United States Due to 14 Foodborne Pathogens" (2012).
Below the estimates for productivity loss are assumptions about the value of reducing the risk of illness by enough to prevent one death in the U.S. population in a typical year. These assumptions are referred to as the value of a statistical life (VSL). In 2018 dollars, the mean VSL is $9,702,616. High and low estimates for the VSL are also given. A more in-depth explanation of the VSL estimates is provided in the report:Making Sense of Recent Cost-of-Foodborne-Illness Estimates
Separate spreadsheets are provided for low, mean and high estimates of the cost of foodborne shigellosis. Each spreadsheet links to the assumptions spreadsheet in the Excel file. All differences in the low, mean, and high estimates are driven by differences in the case estimates in "Foodborne Illness Acquired in the United States—Major Pathogens". It is also possible to vary assumptions regarding the VSL, although this sensitivity analysis is not included in the low, mean and high estimates.
The structure of each of the cost estimates spreadsheets is similar to that of the assumption spreadsheet and references values in the assumptions spreadsheet. In the mean cost estimates spreadsheet, columns F through J contain health outcomes in order of increasing severity. The rows have values for the number of cases, medical treatment costs, lost productivity/wages, and the value of preventing the mortality caused by foodborne shigellosis acquired in the United States in a typical year. These spreadsheets contain formulae linked to the assumptions spreadsheet, which allow the user to create new spreadsheets with assumptions that differ from those provided by ERS.
To understand how total cost of illness is calculated, use the mean cost of illness estimates spreadsheet as an illustration. In a typical year, an average of 1,456 hospitalized cases of foodborne shigellosis recover. During the post-hospitalization recovery period, an average of $211,187 is spent on physician’s visits; nothing is spent on emergency room, outpatient clinic visits, or subsequent hospitalizations; and $260,959 in job productivity is lost due to people needing to recover at home. Adding these two component costs—medical costs and productivity loss—results in a total cost of $472,146 in post-hospitalization recovery from foodborne shigellosis cases in the U.S. in a typical year. Costs for cases of foodborne shigellosis that did not receive medical care averaged $7,332,961 in a typical year; and costs for cases that sought medical care (physician visits) but were not hospitalized averaged $6,873,219. Hospitalized cases cost $47,497,911. Individuals would be willing to pay $97,026,165 to prevent the mean number of deaths expected from foodborne shigellosis acquired in the United States in a typical year. The total cost of these shigellosis cases is calculated by adding across columns the total cost of each health outcome, resulting in a total cost of $159,202,402.