If a co-worker leaves a PC logged into the confidential system, what is the best action?

The best action in this scenario is to log your co-worker off and log in with your own credentials. This action ensures security and compliance with policies regarding access to confidential systems. Leaving a computer logged into a confidential system poses a significant risk, as it could allow unauthorized individuals to access sensitive information. By logging off the co-worker's session, you are mitigating the risk of potential data breaches or unauthorized access to confidential information.

Using your own credentials to log in emphasizes the importance of accountability and traceability in data access. Each user should access systems under their own user ID to ensure that actions can be attributed accurately to the individual who performed them. This practice is a fundamental aspect of maintaining data integrity and complying with healthcare regulations concerning confidentiality and privacy.

The other choices do not effectively address the importance of data protection and compliance with security protocols. Continuing to work under a co-worker's User-ID can introduce security vulnerabilities, as it blurs the lines of accountability. Doing nothing until the co-worker returns fails to address the immediate risk posed by an unattended logged-in session, and merely notifying someone while continuing to work does not take the necessary corrective action to secure the system immediately.