I've known a couple of adults who've had it, and they both said they felt like they'd crack a rib because of the major coughing episodes. One in particular reckoned it wasn't a nice thing to go through at all. Still, I imagine most adults get through it without major worries or complications (... but I honestly don't know how serious it can be with adults).

From our perspective (ie, mums of young kids) it's probably more to do with adults passing it on unaware they've got it. I saw last night where a five week old bub in Adelaide has died in past few days because he/she contracted whooping cough. Too young to be immunised, poor dear and bub's poor parents

Hope your brother is OK and your DP doesn't get it either.