How would you manage a patient with Crohn's disease on a biologic and presents with non-bloody diarrhea, normal-appearing mucosa on sigmoidoscopy but severe colitis on biopsy with a positive CMV stain?  

Would you send a CMV DNA PCR in blood, and if you elect to treat with anti-CMV medication, how long would you treat? What parameters would you use, besides clinical improvement, to decide the duration of therapy or assess treatment failure?