HOUSTON -

A thumb drive containing cancer patients' information has been lost, hospital officials said Friday.

University of Texas MD Anderson Cancer Center officials said an employee lost an unencrypted USB thumb drive on an employee shuttle bus on July 13.

Hospital officials said they became aware of the loss on July 14 and then began searching for it. It has not been found, officials said.

The thumb drive contained information about nearly 2,200 patients, including their names, dates of birth, medical record numbers, diagnoses, treatment and research information, hospital officials said. The drive did not contain Social Security numbers or other financial information, hospital officials said.

The hospital has sent letters to affected patients to make them aware of the situation. Officials said there is no reason to believe that the information has been or will be accessed improperly.

In April, a laptop containing patients' information, including Social Security numbers, was stolen from a doctor's home.