Any disability-related information, such as reasonable accommodation requests, must be maintained by an employer in a separate, confidential file; not in a personnel file. This file will not follow the employee if they leave their current job. If a charge of disability-related discrimination is filed or an action is brought by EEOC, an employer must save all personnel records related to the charge until final disposition of the charge.
For additional information, take a look at the following resources:
Fact Sheet: Reasonable Accommodations in the Workplace