<qa>  What is the first episode of CDI defined as?SER-262-001 is a Phase 1b, randomized, double blind, placebo-controlled, ascending single dose clinical study with 2 treatment arms SER-262 or placebo in up to 5 dose cohorts. Patients who have been diagnosed with their first primary episode of CDI, defined as diarrhea 3 unformed stools per day for 2 consecutive days, a positive C. difficile stool test and who have responded to standardofcare antibiotic will receive investigational drug or placebo on Day 1. 