Our objective of this study is to derive a real incidence of CDI in tertiary hospitals located through Korean peninsula. In order to get a close value to the truth, the study is planned to co-perform with a national study which was proposed in evaluation process to include more hospitals. Along with the incidence of CDI, clinical characteristics and outcome of CDI will be examined and microbiologic characteristics of C. difficile isolates from CDI patients are studied.

Inclusion Criteria:

• aged older than 19 years
• more than 3 times of unformed stools passage per day
• positive results of toxin gene test: GDH (+) + PCR (+), GDH (+) + toxin (+), or PCR (+) + toxin (+)
• agree with informed consent

Exclusion Criteria:

• less than 3 times of unformed stool passage per day
• use of oral metronidazole or vancomycin more than 24 hours before enrollment
• use of laxative before enrollment
• recurrent episode of CDI
• disagree with study protocol

The patients who admitted at the tertiary hospitals in Korea and and diagnosed as Clostridioides difficile infection will be selected.

The tertiary hospitals located in Seoul-si, Gyeonggi-do, Pusan-si, Daegu-si, Jeollanam-do, Jeollabuk-do, and Chungcheongbuk-do. These hospitals distributes all over the country.