Can an employer refuse to hire an employee whose disability would present a health risk to himself or others?

Yes, an employer does not violate the ADA if the employer refuses to hire an employee who poses a direct to others or himself on the job. In Chevron U.S.A. v. Echazabal (2002), the U.S. Supreme Court unanimously ruled that an employer did not violate the ADA when it refused to hire a former employee whose disability (hepatitis and liver problems) would be exacerbated by exposure to toxins in the workplace. The Court reasoned that the direct-threat defense articulated in federal regulations should also extend to workers who posed a danger to themselves. The Court did say that the direct-threat defense must be based on reasoned medical judgment and should not used as a guise to discriminate against disabled workers who don’t truly pose a threat at all.