CDI recurrence is defined as the development of a new episode of diarrhea (3 or more loose stools in 24 or fewer hours) and a positive local or central lab stool test for toxigenic Clostridium (C.) difficile following clinical cure of the initial CDI episode

Participants who received infusion of study medication; had a positive local stool test for toxigenic C. difficile; received protocol defined standard of care therapy within 1 day window of the infusion; and complied with Good Clinical Practice.

Global Cure is defined as the clinical cure of the initial CDI episode and no CDI recurrence through Week 12. Clinical cure is defined as participants who received ≤ 14 day regimen of SOC therapy and have no diarrhea (≤2 loose stools per 24 hours) for two consecutive days following completion of SOC therapy for the initial CDI episode.

Participants who received infusion of study medication; had a positive local stool test for toxigenic C. difficile; received protocol defined standard of care therapy within 1 day window of the infusion; and complied with Good Clinical Practice.

CDI recurrence is defined as the development of a new episode of diarrhea (3 or more loose stools in 24 or fewer hours) and a positive local or central lab stool test for toxigenic C. difficile following clinical cure of the initial CDI episode. Clinical cure is defined as participants who received ≤ 14 day regimen of SOC therapy and have no diarrhea (≤2 loose stools per 24 hours) for two consecutive days following completion of SOC therapy for the baseline CDI episode.

Participants who received infusion of study medication; had a positive local stool test for toxigenic C. difficile; received protocol defined standard of care therapy within 1 day window of the infusion; complied with Good Clinical Practice; and achieved clinical cure of the initial CDI episode.

An AE is defined as any untoward medical occurrence in a clinical investigation participant administered a pharmaceutical product and which does not necessarily have to have a causal relationship with this treatment. An AE can therefore be any unfavorable and unintended signs (including an abnormal laboratory finding, for example), symptom, or disease temporally associated with the use of a medicinal product or protocol-specific procedure, whether or not considered related to the medicinal product or protocol specific procedure. Any worsening (i.e., any clinically significant adverse change in frequency and/or intensity) of a preexisting condition that is temporally associated with the use of the Sponsor's product, is also an AE.

All randomized participants who received infusion of study medication, based on the treatment actually received. One participant randomized to receive MK-3415A, and two participants randomized to receive MK-6072 actually received placebo instead.

An AE is defined as any untoward medical occurrence in a clinical investigation participant administered a pharmaceutical product and which does not necessarily have to have a causal relationship with this treatment. An AE can therefore be any unfavorable and unintended signs (including an abnormal laboratory finding, for example), symptom, or disease temporally associated with the use of a medicinal product or protocol-specific procedure, whether or not considered related to the medicinal product or protocol specific procedure. Any worsening (i.e., any clinically significant adverse change in frequency and/or intensity) of a preexisting condition that is temporally associated with the use of the Sponsor's product, is also an AE. A drug-related AE was an AE determined by the investigator to be related to the drug.

All randomized participants who received infusion of study medication, based on the treatment actually received. One participant randomized to receive MK-3415A, and two participants randomized to receive MK-6072 actually received placebo instead.

A SAE is any AE occurring at any dose or during any use of Sponsor's product that: results in death; or is life threatening; or results in a persistent or significant disability/incapacity; or results in or prolongs an existing inpatient hospitalization; or is a congenital anomaly/birth defect; or is a cancer, or is associated with an overdose (whether accidental or intentional); or is other important medical events.

All randomized participants who received infusion of study medication, based on the treatment actually received. One participant randomized to receive MK-3415A, and two participants randomized to receive MK-6072 actually received placebo instead.

A SAE is any AE occurring at any dose or during any use of Sponsor's product that: results in death; or is life threatening; or results in a persistent or significant disability/incapacity; or results in or prolongs an existing inpatient hospitalization; or is a congenital anomaly/birth defect; or is a cancer, or is associated with an overdose (whether accidental or intentional); or is other important medical events. A serious drug-related AE was a SAE determined by the investigator to be related to the drug.

All randomized participants who received infusion of study medication, based on the treatment actually received. One participant randomized to receive MK-3415A, and two participants randomized to receive MK-6072 actually received placebo instead.

An AE is defined as any untoward medical occurrence in a clinical investigation participant administered a pharmaceutical product and which does not necessarily have to have a causal relationship with this treatment. An AE can therefore be any unfavorable and unintended signs (including an abnormal laboratory finding, for example), symptom, or disease temporally associated with the use of a medicinal product or protocol-specific procedure, whether or not considered related to the medicinal product or protocol-specific procedure. Any worsening (i.e., any clinically significant adverse change in frequency and/or intensity) of a preexisting condition that is temporally associated with the use of the Sponsor's product, is also an AE.

All randomized participants who received infusion of study medication, based on the treatment actually received. One participant randomized to receive MK-3415A, and two participants randomized to receive MK-6072 actually received placebo instead.

Infusion-specific AEs included local infusion site AEs; and systemic AEs which include nausea, vomiting, chills, fatigue, feeling hot, infusion site conditions (bruising, coldness, erythema, extravasation, pain, phlebitis, pruritus), pyrexia, arthralgia, musculoskeletal pain, myalgia, dizziness, headache, dysphonia, nasal congestion, pruritus, rash, pruritic rash, urticaria, flushing, hot flush, hypertension, and hypotension.

All randomized participants who received infusion of study medication, based on the treatment actually received. One participant randomized to receive MK-3415A, and two participants randomized to receive MK-6072 actually received placebo instead.

CDI recurrence is defined as the development of a new episode of diarrhea (3 or more loose stools in 24 or fewer hours) and a positive local or central lab stool test for toxigenic C. difficile following clinical cure of the initial CDI episode.

Participants ≥ 65 years of age at study entry who received infusion of study medication; had a positive local stool test for toxigenic C. difficile; received protocol defined standard of care therapy within 1 day window of the infusion; and complied with Good Clinical Practice.

CDI recurrence is defined as the development of a new episode of diarrhea (3 or more loose stools in 24 or fewer hours) and a positive local or central lab stool test for toxigenic C. difficile following clinical cure of the initial CDI episode.

Participants with a history of CDI in the 6 months prior to enrollment who received infusion of study medication; had a positive local stool test for toxigenic C. difficile; received protocol defined standard of care therapy within 1 day window of the infusion; and complied with Good Clinical Practice.

CDI recurrence is defined as the development of a new episode of diarrhea (3 or more loose stools in 24 or fewer hours) and a positive local or central lab stool test for toxigenic C. difficile following clinical cure of the initial CDI episode. Clinically severe CDI is defined as a Zar Score ≥ 2 based on the presence of 1 or more of the following: 1) age >60 years old (1 point); 2)body temperature >38.3°C (>100°F) (1 point); 3) albumin level ˂2.5 mg/dL (1 point); 4) peripheral white blood cell count >15,000 cells/mm^3 within 48 hours (1 point); 5) endoscopic evidence of pseudomembranous colitis (2 points); and 6) treatment in Intensive Care Unit (2 points).

Participants with clinically severe CDI at study entry who received infusion of study medication; had a positive local stool test for toxigenic C. difficile; received protocol defined standard of care therapy within 1 day window of the infusion; and complied with Good Clinical Practice.

CDI recurrence is defined as the development of a new episode of diarrhea (3 or more loose stools in 24 or fewer hours) and a positive local or central lab stool test for toxigenic C. difficile following clinical cure of the initial CDI episode.

Participants with the B1/NAP1/027 strain of C. difficile at study entry who received infusion of study medication; had a positive local stool test for toxigenic C. difficile; received protocol defined standard of care therapy within 1 day window of the infusion; and complied with Good Clinical Practice.

CDI recurrence is defined as the development of a new episode of diarrhea (3 or more loose stools in 24 or fewer hours) and a positive local or central lab stool test for toxigenic C. difficile following clinical cure of the initial CDI episode.

Participants with an epidemic strain of C. difficile at study entry who received infusion of study medication; had a positive local stool test for toxigenic C. difficile; received protocol defined standard of care therapy within 1 day window of the infusion; and complied with Good Clinical Practice.

CDI recurrence is defined as the development of a new episode of diarrhea (3 or more loose stools in 24 or fewer hours) and a positive local or central lab stool test for toxigenic C. difficile following clinical cure of the initial CDI episode. Compromised immunity is defined as follows: an active hematological malignancy (including leukemia, lymphoma, multiple myeloma), an active malignancy requiring recent cytotoxic chemotherapy, receipt of a prior hematopoietic stem cell transplant, receipt of a prior solid organ transplant, asplenia, or neutropenia/pancytopenia due to other conditions.

Participants with compromised immunity at study entry who received infusion of study medication; had a positive local stool test for toxigenic C. difficile; received protocol defined standard of care therapy within 1 day window of the infusion; and complied with Good Clinical Practice.