My husband 49 years old  had fever for a day followed by mild upset stomach for a period of 2-3 days after he consumed outside food around 9-10 days back.Since then his stool is semi solid to semi liquid consistency whenever he eats full meal food with gluten or fiber rich fruit or citric and wholegrain.Eating rice or banana works well to reverse stool consistency. Surprisingly his CBC with ESR report came absolutely normal.What can be the cause since mild fever still suggested infection of may be bacteria? What tests to be conducted for a clear picture?