word choice - If you can't use “he”, “she” or “they” in a sentence, what do you use?

I was waiting for a plane to take off last week, when we had to taxi back to the terminal building to disembark a sick passenger. We weren't told whether the passenger was male or female.

I was thinking about how to tell people about it, but realised I couldn't say that 'He' or 'She' disembarked, because I didn't know the sex. I couldn't say 'They' because I knew there was only one and I couldn't say 'It', because it wasn't an object. Without saying 'The sick passenger' disembarked, what word could I use?