Don't Ever Get Sick at Granny's (Ghosts of Fear Street #16) by R.L. Stine, Jahnna N. Malcolm - Vintage Paperback

Visiting his Granny Marsha's house for the weekend, Corey comes down with a cold, a situation that skyrockets out of control when his Granny's determination to kill every germ in his body turns her into a crazed person.