I think that doing the kilomathon with less than ideal training is safer than running with a chest infection.
Get thee to bed with medicine and make your partner wait on you hand and foot. You're not getting better because you're not letting your body and the antibiotics do their thing.
Call in sick, stay in bed and you'll be better in a week and can spend two weeks gradually building your running again. If you really want to do the kilomathon (I don't know how far that is so pardon the ignorance - am guessing 26.2K?) then do it as a training run, go gently and maybe consider run/walk (you could take one minute walk break every mile/2K/whatever works). If you're not better, don't do it!