The USDA posts public data containing the results of every salmonella sample it takes at poultry processing plants nationwide, detailing when it took the sample, what type of poultry it sampled and whether or not it found salmonella. If salmonella was present, the records include information on the type of salmonella found and whether it was resistant to antibiotics.

While the USDA splits these into different files based on type of poultry — for example, ground chicken or whole turkey — and sample date, we combined the data into one file. The USDA uses this information to categorize plants based on whether or not they achieved the agency’s salmonella targets. ProPublica used this sampling dataset to calculate the salmonella positivity rates shown in the Chicken Checker app. While our app uses the most recent 52 weeks of data available, we are including all samples that have been available on the app since its publication.