The Centers for Disease Control and Prevention has issued a warning that a salmonella outbreak believed to be linked to onions imported from Chihuahua, Mexico, has spread to 37 states — sickening over 650 people. The CDC directed businesses on Wednesday evening to stop selling fresh whole red, white, or yellow onions that were imported from Chihuahua and distributed by ProSource Inc. It also suggested businesses clean any surfaces that may have touched such onions. The agency urged Americans to throw away any whole red, white, or yellow onions that don’t have a sticker or packaging. People should also throw out onions that have stickers or packaging identifying the brand ProSource and Mexico as the country of origin, the agency said. “If you can’t tell where the onions are from, don’t buy or eat them,” the CDC said in a statement.