In July 2010, CDC and public health officials in multiple states investigated two concurrent outbreaks of Salmonella infections, each involving a different Salmonella serotype: Hartford and Baildon. Both of these Salmonella serotypes are rare, and ill persons in both outbreaks had similar age and geographic distribution. By August 1, there were a total of 75 individuals infected with a matching strain of Salmonella Hartford from 15 states, and a total of 80 individuals infected with a matching strain of Salmonella Baildon from 15 states.

Among those infected with Salmonella Hartford, illnesses began between April 30 and July 18, 2010. Among those infected with Salmonella Baildon, illness began between May 11 and July 19, 2010.

The CDC and public health officials launched an epidemiologic study comparing foods eaten by ill and well persons. The study found that ill persons were significantly more likely than well persons to report eating at Taco Bell in the week before illness. The FDA worked with the CDC to conduct a traceback investigation but found that no specific food item or ingredient was associated with the illness. There were also no common Taco Bell locations reported by ill persons in both the outbreaks.

According to the update provided by the CDC on August 4, 2010, the 75 cases associated with the Salmonella Hartford outbreak include individuals from: Colorado (1), Florida (1) Georgia (1), Illinois (5), Indiana (11), Kentucky (23), Massachusetts (2), Michigan (3), Montana (1), North Carolina (1), New Hampshire (1), New York (1), Ohio (19), Pennsylvania (1), and Wisconsin (4). The 80 cases associated with the Salmonella Baildon outbreak include individuals from: Connecticut (1), Georgia (1), Iowa (1), Illinois (20), Indiana (4), Kentucky (5), Massachusetts (1), Michigan (4), Minnesota (5), New Jersey (6), New York (2), Ohio (6), Oregon (1), Washington (1), and Wisconsin (22).