My ds10 was hospitalized with bacterial meningitis when he was three, and running a rectal temp. of 105-106. They'd only take his temp rectally because they needed the accuracy. When they'd do it orally or in his ear, they'd add a degree, when done under his arm, they'd add 2 degrees. That was nearly seven years ago, so I don't know if ear thermometers have become more sensitive; but at the hospital, they never really regarded them as accurate as rectal temps.