In the United States, 325,000 hospitalizations and 5,000 deaths a year are caused by foodborne illness, according to the Centers for Disease Control. Most of these cases could be prevented by proper handling of food.
Yogurt
Yogurt is essentially heated milk with Streptococcus thermophilus and Lactobacillus bulgaricus added. During the fermentation process, these good bacterias convert the pasteurized milk to yogurt. The milk is usually pasteurized to prevent harmful bacteria from growing.
Refrigeration
Yogurt, as a dairy product, can spoil quickly if it is not properly stored. Bacteria grows at room temperature and yogurt must remain refrigerated at temperatures in between 34 to 40 degrees. If kept tightly covered it should remain good for up to 10 days. Once opened, it should be used within three to four days.
Expiration Date
Yogurt is sold with an expiration date, or a "sell by" date. These dates should be taken into consideration. Never buy yogurt that is past its expiration date. The "sell by" date indicates the day which it must leave the store. It will be good for another seven days if kept refrigerated.
References
McKinley Health Center: Food SafetyAbout Yogurt: Live CultureStraighten Up Now: Dairy Storage Tips