Can a pumpkin pie be left unrefrigerated outside in 45 degree weather?

It is not safe to leave a pumpkin pie unrefrigerated outside in 45 degree weather. The USDA recommends refrigerating pumpkin pie within two hours of baking to prevent the growth of harmful bacteria. Even at 45 degrees Fahrenheit, bacteria can still grow on the pie, causing spoilage and increasing the risk of foodborne illness. It's best to keep the pumpkin pie refrigerated until ready to serve and discard any leftovers after four days.