A Salmonella outbreak in Owosso, Mich., first reported earlier this month has been linked to local Mexican restaurant El Potrero, though investigators have not found any contamination during inspections. At least 13 people have fallen ill in an outbreak apparently connected to the restaurant. All food samples taken from the restaurant have tested negative for Salmonella and health officials have found nothing wrong at the restaurant during inspections, the owners to the Argus-Press newspaper. Investigators were most interested in testing the restaurant’s salsa and canned tomatoes. Patrons of El Potrero developed Salmonella illnesses around the end of July. Health officials have visited the restaurant three times trying to determine how it might be connected to the outbreak. The investigation remains ongoing. El Potrero has been in business for 10 years, with four locations in Owosso, Flint and Swartz Creek.