Anytime fluid rests in the middle of the ear and develops an infection, the bacteria can spread throughout the ear. In most cases, the fluid will run down the tube or become absorbed by the body. Still, this is not fool-proof. There are many reasons why your child may still experience an ear infection in spite of having the tubes in place.
Inflammation is common in the nose and throat, and this can spread to the ear tube. The result is closure of the tube, ultimately trapping infected fluid inside the ear. A dastardly ear infection is the result. While it is not common, it is possible.