Philip J. Cheng is a Doctor.
Philip Cheng was a resident at Harvard's Brigham and Women's Hospital,
Philip nicked himself while preparing an HIV Positive patient for Surgery. Following Hospital protocol, Cheng took 1 month of Truvada, a mixture of two HIV medications, to reduce his risk of contracting HIV. This process is known as Pre-exposure prophylaxis, intended to curb risks of diseases. 
Philip decided to keep taking Truvada since he is Homosexual and wanted to reduce his risk of contracting HIV.
When Philip applied for Disability insurance, he was only offered a 5 year plan due to his use of Truvada. He was deemed to be engaging in high-risk sexual activity.
Philip claimed he was in a monogamous relationship with an HIV-negative man, and therefore he should not be denied a lifetime of coverage. The insurance company pointed out that Truveda is not 100% effective at preventing HIV, and since gay men are over 100x more likely to contract STDs like HIV, they could not insure him for life. In addition, it was argued that there is no way to guarantee that Cheng's monogamous relationship would last for the duration of the coverage, nor was the fidelity of Cheng's partner guaranteed.