[DVSNCYNIKL]

I had the same problem with my Accord. Apparently it had something to do with the fact that the person before always kept the vents recirculating the same air instead of leaving it open to take air from the outside. I did the same thing in what your brother did. That smell is stuck to the channels where the air is coming through. Tell him to just leave the vents open to pull from the outside and use them often to clean them out. I've heard some people just spray disinfectant or some form of air freshner directly into the vents themselves. Hope that helps.