What if an employee is fired from a healthcare facility for being COVID positive after having been exposed at the workplace?

What if an employee is fired from a healthcare facility for being COVID positive after having been exposed at the workplace?
You would have multiple issues. CARES Act provisions would make employee eligible for specific unemployment benefits. Exposure at workplace would make it a potential workers' compensation case. The termination because of and following exposure would make for a potential retaliatory discharge claim under Sec.451 of Workers' Compensation Act:

Sec. 451.001. DISCRIMINATION AGAINST EMPLOYEES PROHIBITED. A person may not discharge or in any other manner discriminate against an employee because the employee has:

(1) filed a workers' compensation claim in good faith;

(2) hired a lawyer to represent the employee in a claim;

(3) instituted or caused to be instituted in good faith a proceeding under Subtitle A; or

(4) testified or is about to testify in a proceeding under Subtitle A.

Would that make out a claim under the Americans for Disability Act?

That's possible, but I see some potential issues. For one thing my understanding is onus is on employee to show how the work could be done with a reasonable accommodation. There's probably not a reasonable accommodation under the standard of care for healthcare workers under these circumstances. A short leave of absence may be a reasonable accommodation, however. The employee is likely going to come out way better with a quicker resolution file workers comp, getting enhanced unemployment benefits, and filing suit to claim retaliation if unable to find new work when client recovers in a few weeks. Each case will vary.