You'll need a few items to prepare for this achievement. You'll need several healing items and a phenocyline jab. Heads to lud's Holm, the Bobby on guard at the bridge will give you a phenocyline jab. Whilst in lud's Holm, you'll be attacked by a plague infected wastrel straight away, let him keep hitting you until you become infected. It may take one hit, it may take twenty hits, hence the healing items. When you do become infected, use the phenocyline jab immediately and your achievement will pop. If for some reason this guy doesn't infect you, other plague victims only come out at night and have some sort of swarm around thier heads, as well as acting crazy! Also I found wearing the torn suit as opposed to the padded suit got me infected quicker. Hope this helps.
Edit: as pointed out in the comments, you'll know you're infected by a red biohazard symbol appearing in the top left of your husband.
Another Edit: seems a few people keep taking hits without getting infected. Whilst playing as Sally, I couldn't search the body of a plague victim without getting infected, so try repeatedly searching bodies and you could pick up the plague that way!