Initial clinical response (ICR) for ages from birth to < 2 years was defined as absence of watery diarrhea for 2 consecutive treatment days, remaining well until study drug discontinuation. ICR for ages ≥ 2 years to < 18 years was defined as improvement in number and character of bowel movements as determined by < 3 unformed bowel movements (UBMs) per day for 2 consecutive treatment days, remaining well until study drug discontinuation. CCR was defined for both age groups as not requiring further CDAD therapy within 2 days after study drug completion, and was reported with a positive (Yes) or negative (No) outcome. Resolution of diarrhea was assessed during interviews of participant/parent/legal guardian, supplemented by review of personal records (if hospitalized) and checked for presence of watery diarrhea (ages from birth to < 2 years) or number of UBMs (for ages ≥ 2 years to < 18 years).

The analysis population consisted of the full analysis set (FAS) which consisted of all randomized participants who received at least 1 dose of study drug. In the FAS, participants were allocated to the treatment arm corresponding to the study medication that the participant was randomized to (treatment allocation as randomized).

SCR at EOT + 9 days was defined as CCR (EOT + 2 days) without CDAD recurrence until assessment at EOT +9 days during the follow-up period. Recurrence for ages from birth to < 2 years was defined as re-establishment of watery diarrhea after CCR to an extent that was greater than that noted on the last day of study drug with positive direct or indirect testing for the presence of toxigenic Clostridium difficile (C. difficile) in stool and that, in the investigator's opinion, required retreatment with CDAD anti-infective therapy. Recurrence for ages ≥ 2 years < 18 years was defined as re-establishment of diarrhea after CCR to an extent (as measured by the frequency of UBMs) that was greater than that noted on the last day of study drug with positive direct or indirect testing for the presence of toxigenic C. difficile in stool and that, in the investigator's opinion, required retreatment with CDAD anti-infective therapy.

The analysis population consisted of the FAS (participants with CCR at EOT +2 days).

GC was reported as a positive (Yes) or negative (No) outcome and was calculated using SCR and ICR/CCR values according to the following conditions: ● if ICR/CCR=Yes and SCR=Yes, then Global Cure was Yes. ● if ICR/CCR=Yes and SCR =No, then Global Cure was No. ● if ICR/CCR=No (SCR not assessed), then Global Cure was No. ● if ICR/CCR=Missing (SCR not assessed), then Global Cure was set to No. No multiple imputation method (MI) was used for global cure at EOT + 9 days.

The analysis population consisted of the FAS.

Recurrence for ages from birth to < 2 years was defined as re-establishment of watery diarrhea after CCR to an extent that was greater than that noted on the last day of study drug with positive direct or indirect testing for the presence of toxigenic C. difficile in stool and that, in the investigator's opinion, required retreatment with CDAD anti-infective therapy. Recurrence for ages ≥ 2 years < 18 years was defined as re-establishment of diarrhea after CCR to an extent (as measured by the frequency of UBMs) that was greater than that noted on the last day of study drug with positive direct or indirect testing for the presence of toxigenic C. difficile in stool and that, in the investigator's opinion, required retreatment with CDAD anti-infective therapy.

The analysis population consisted of the FAS (participants with CCR at EOT +2 days).

SCR at EOT + 16 days was defined as CCR (EOT + 2 days) without CDAD recurrence until assessment at EOT + 16 days during the follow-up period. Recurrence for ages from birth to < 2 years was defined as re-establishment of watery diarrhea after CCR to an extent that was greater than that noted on the last day of study drug with positive direct or indirect testing for the presence of toxigenic C. difficile in stool and that, in the investigator's opinion, required retreatment with CDAD anti-infective therapy. Recurrence for ages ≥ 2 years < 18 years was defined as re-establishment of diarrhea after CCR to an extent (as measured by the frequency of UBMs) that was greater than that noted on the last day of study drug with positive direct or indirect testing for the presence of toxigenic C. difficile in stool and that, in the investigator's opinion, required retreatment with CDAD anti-infective therapy.

The analysis population consisted of the FAS (participants with CCR at EOT +2 days).

GC was reported as a positive (Yes) or negative (No) outcome and was calculated using SCR and ICR/CCR values according to the following conditions: ● if ICR/CCR=Yes and SCR=Yes, then Global Cure was Yes. ● if ICR/CCR=Yes and SCR =No, then Global Cure was No. ● if ICR/CCR=No (SCR not assessed), then Global Cure was No. ● if ICR/CCR=Missing (SCR not assessed), then Global Cure was set to No. No multiple imputation method (MI) was used for global cure at EOT + 16 days.

The analysis population consisted of the FAS.

Recurrence for ages from birth to < 2 years was defined as re-establishment of watery diarrhea after CCR to an extent that was greater than that noted on the last day of study drug with positive direct or indirect testing for the presence of toxigenic C. difficile in stool and that, in the investigator's opinion, required retreatment with CDAD anti-infective therapy. Recurrence for ages ≥ 2 years < 18 years was defined as re-establishment of diarrhea after CCR to an extent (as measured by the frequency of UBMs) that was greater than that noted on the last day of study drug with positive direct or indirect testing for the presence of toxigenic C. difficile in stool and that, in the investigator's opinion, required retreatment with CDAD anti-infective therapy.

The analysis population consisted of the FAS (participants with CCR at EOT +2 days).

SCR at EOT + 23 days was defined as CCR (EOT + 2 days) without CDAD recurrence until assessment at EOT + 16 days during the follow-up period. Recurrence for ages from birth to < 2 years was defined as re-establishment of watery diarrhea after CCR to an extent that was greater than that noted on the last day of study drug with positive direct or indirect testing for the presence of toxigenic C. difficile in stool and that, in the investigator's opinion, required retreatment with CDAD anti-infective therapy. Recurrence for ages ≥ 2 years < 18 years was defined as re-establishment of diarrhea after CCR to an extent (as measured by the frequency of UBMs) that was greater than that noted on the last day of study drug with positive direct or indirect testing for the presence of toxigenic C. difficile in stool and that, in the investigator's opinion, required retreatment with CDAD anti-infective therapy.

The analysis population consisted of the FAS (participants with CCR at EOT +2 days).

GC was reported as a positive (Yes) or negative (No) outcome and was calculated using SCR and ICR/CCR values according to the following conditions: ● if ICR/CCR=Yes and SCR=Yes, then Global Cure was Yes. ● if ICR/CCR=Yes and SCR =No, then Global Cure was No. ● if ICR/CCR=No (SCR not assessed), then Global Cure was No. ● if ICR/CCR=Missing (SCR not assessed), then Global Cure was set to No. No multiple imputation method (MI) was used for global cure at EOT + 23 days.

The analysis population consisted of the FAS.

Recurrence for ages from birth to < 2 years was defined as re-establishment of watery diarrhea after CCR to an extent that was greater than that noted on the last day of study drug with positive direct or indirect testing for the presence of toxigenic C. difficile in stool and that, in the investigator's opinion, required retreatment with CDAD anti-infective therapy. Recurrence for ages ≥ 2 years < 18 years was defined as re-establishment of diarrhea after CCR to an extent (as measured by the frequency of UBMs) that was greater than that noted on the last day of study drug with positive direct or indirect testing for the presence of toxigenic C. difficile in stool and that, in the investigator's opinion, required retreatment with CDAD anti-infective therapy.

The analysis population consisted of the FAS (participants with CCR at EOT +2 days).

SCR at EOS was defined as CCR (EOT + 2 days) without CDAD recurrence until assessment at EOS (EOT + 30 days) during the follow-up period. Recurrence for ages from birth to < 2 years was defined as re-establishment of watery diarrhea after CCR to an extent that was greater than that noted on the last day of study drug with positive direct or indirect testing for the presence of toxigenic C. difficile in stool and that, in the investigator's opinion, required retreatment with CDAD anti-infective therapy. Recurrence for ages ≥ 2 years < 18 years was defined as re-establishment of diarrhea after CCR to an extent (as measured by the frequency of UBMs) that was greater than that noted on the last day of study drug with positive direct or indirect testing for the presence of toxigenic C. difficile in stool and that, in the investigator's opinion, required retreatment with CDAD anti-infective therapy.

The analysis population consisted of the FAS (participants with CCR at EOT +2 days).

GC was reported as a positive (Yes) or negative (No) outcome and was calculated using SCR and ICR/CCR values according to the following conditions: ● if ICR/CCR=Yes and SCR=Yes, then Global Cure was Yes. ● if ICR/CCR=Yes and SCR =No, then Global Cure was No. ● if ICR/CCR=No (SCR not assessed), then Global Cure was No. ● if ICR/CCR=Missing (SCR not assessed), then Global Cure was set to No. Global Cure at EOT +30 days was derived using MI in case ICR/CCR=Missing (SCR not assessed) following Rubin's multiple imputation method.

The analysis population consisted of the FAS.

Recurrence for ages from birth to < 2 years was defined as re-establishment of watery diarrhea after CCR to an extent that was greater than that noted on the last day of study drug with positive direct or indirect testing for the presence of toxigenic C. difficile in stool and that, in the investigator's opinion, required retreatment with CDAD anti-infective therapy. Recurrence for ages ≥ 2 years < 18 years was defined as re-establishment of diarrhea after CCR to an extent (as measured by the frequency of UBMs) that was greater than that noted on the last day of study drug with positive direct or indirect testing for the presence of toxigenic C. difficile in stool and that, in the investigator's opinion, required retreatment with CDAD anti-infective therapy.

The analysis population consisted of the FAS (participants with CCR at EOT +2 days).

TTROD for ages from birth < 2 years was defined as time elapsing (hours rounded up from minutes > 30) from treatment start (time of first study drug dose) to diarrhea resolution (time of last episode of watery diarrhea the day prior to the first of 2 consecutive days without watery diarrhea sustained through EOT). TTROD for ages ≥ 2 years to < 18 years was defined as time elapsing (hours rounded up from minutes > 30) from treatment start (time of first dose) to diarrhea resolution (time of the last UBM the day prior to the first of 2 consecutive days of < 3 UBMs sustained through EOT). TTROD by Kaplan-Meier Method. Those who completed treatment but did not show diarrhea resolution until EOT were censored at Day 10/240 hours. Those who did not complete treatment, discontinued earlier but did not show diarrhea resolution until disc. day were censored at disc. (days converted to hours). Those whose diarrhea did not continue after first dose were included with a TTROD of 1 hour.

The analysis population consisted of the FAS.

Time to recurrence was defined as the time (days) from CCR until the onset of recurrence. Time to recurrence of CDAD by Kaplan-Meier Method. Data for median was estimated and the 95% CI could not be estimated due to low event rate. Data not estimable denoted as NA. Participants with CCR at EOT+2 days, who completed the follow-up period but did not experience a recurrence of CDAD were censored at EOT+30 days and those who did not complete the follow-up period and discontinued during this period and did not experience a recurrence of CDAD were censored at day of discontinuation.

The analysis population consisted of the FAS (participants with CCR at EOT +2 days).

An adverse event (AE) was defined as any untoward medical occurrence in a participant administered a study drug or who had undergone study procedures which did not necessarily have a causal relationship with this treatment. This included abnormal laboratory tests, vital signs, electrocardiogram data or physical examinations that were defined as AEs if the abnormality induced clinical signs or symptoms, required active intervention, interruption or discontinuation of study drug or was clinically significant in the investigator's opinion. The following standard with 3 grades was used to measure the severity of AEs, including abnormal clinical laboratory values: ● Mild: No disruption of normal daily activities ● Moderate: Affected normal daily activities ● Severe: Inability to perform daily activities. A treatment-emergent adverse event (TEAE) was defined as an AE observed after starting administration of the test drug/comparative drug.

The analysis population consisted of the safety analysis set (SAF), which consisted of all randomized participants who received at least 1 study drug dose. In the SAF, participants were allocated to the treatment arm corresponding to study drug first administered (fidaxomicin or vancomycin), even if it differed from the treatment randomized to.

Drug concentration was derived from the blood samples collected.

The analysis population consisted of the pharmacokinetics analysis set (PKAS). The PKAS consisted of all participants randomized to fidaxomicin, having received at least 1 dose of fidaxomicin and having at least 1 valid measurement of plasma concentration or fecal concentration of fidaxomicin or its main metabolite OP-1118.

Drug concentration was derived from the blood samples collected.

The analysis population consisted of the PKAS.

Drug concentration was derived from the blood samples collected.

The analysis population consisted of the PKAS.

Drug concentration was derived from the stool samples collected.

The analysis population consisted of the PKAS.

Drug concentration was derived from the stool samples collected.

The analysis population consisted of the PKAS.

Drug concentration was derived from the stool samples collected.

The analysis population consisted of the PKAS.

Acceptance of formulation was evaluated in all participants who received fidaxomicin oral suspension and vancomycin oral liquid (i.e., participants from birth to =< 6 years and participants > 6 years unable to swallow tablets) by means of a five-point rating scale (awful, poor, fair, good, excellent) by unblinded staff if hospitalized, and by the participant/parents/legal guardian when at home.

The analysis population consisted of the FAS.