The Danbury Health Department is alerting residents to a large Salmonella outbreak in 37 states.  The CDC says it's been caused by fresh whole onions and urged everyone to throw away any unlabeled onions they have at home.  Four people in Connecticut have reported illness.  The alert says people should not eat, sell, or serve red, white, or yellow onions imported from Mexico and distributed across the U.S. by ProSource Inc. If it's unclear if an onion is from ProSource, people are encouraged not to buy or eat it.