1. Are employees obliged to disclose themselves as a "risk-factor" to the employer?
Yes, due to the duty of loyalty, employees with a confirmed infection or suspicious symptoms need to disclose this to the employer.
2. Can the employer demand employees to disclose themselves as being a "risk-factor"?
Yes. The employer is entitled to ask an employee whether he/she has spent his/her holiday in a risk area. Due to its duty of care, the employer may then have to take appropriate measures in order to protect the other employees from infection.