In a report published Thursday in the New England Journal of Medicine, scientists from the Centers for Disease Control and Prevention and state health departments recount how they tracked the source of the massive Salmonella outbreak linked to peanut products in 2008 and 2009.

Two key factors in solving the puzzle were identifying clusters and single cases of infection at nine institutions, and reviewing invoices for foods common among the institutions. These steps led investigators to a single brand of institutional peanut paste made by the Peanut Corporation of America.

Here’s the outbreak recap, by the numbers:

States reporting illnesses: 46

Confirmed illnesses: 714

Deaths: 9

Hospitalizations: 166

Number of products recalled: 3,918

Possible causes of contamination at PCA’s Georgia plant include rainwater leaks, raw and roasted peanuts stored in proximity, and inadequate roaster temperatures.

The report says the outbreak resulted in some food safety reforms, notably the Food and Drug Administration’s Reportable Food Registry, which requires companies to notify the FDA of potentially contaminated food within 24 hours.