Determine if the addition of C. difficile toxin A and toxin B human monoclonal anti-toxin antibodies to standard of care treatment reduces the number of subjects with recurrent CDAD compared to standard of care and placebo. Standard of care treatment is defined as receipt of either metronidazole by mouth or parenterally or receipt of vancomycin by mouth with a standard duration of treatment defined as 10 - 14 days (+ 2 days)). Recurrence of CDAD is defined as the development of a new episode of C. difficile disease associated with a positive C. difficile stool toxin(s) test after the resolution of prior episode and after discontinuation of SOC treatment.

200 subjects who met the eligibility criteria and signed the informed consent and received standard of care treatment randomized 1:1 treatment allocation to receive study treatment: 101 subjects in the GS-CDA1/MDX-1388 (Monoclonal antibody (Mab)) treatment group and 99 subjects in the placebo treatment group

Safety and tolerability of a C. difficile toxin A human monoclonal antibody combined with a human monoclonal antibody to C. difficile toxin B in patients receiving standard of care treatment for C. difficile associated disease (CDAD) compared to those patients receiving standard of care and placebo reporting system organ class (SOC) MedDRA V.9.0

200 subjects who met the eligibility criteria and signed the informed consent and received standard of care treatment randomized 1:1 treatment allocation to receive study treatment: 101 subjects in the GS-CDA1/MDX-1388 (Monoclonal antibody (Mab)) treatment group and 99 subjects in the placebo treatment group

Determine if the addition of a C. difficile toxin A human monoclonal antibody combined with C. difficile toxin B human monoclonal antibody to standard of care treatment reduces the time to resolution of diarrhea in patients with CDAD compared to those patients receiving standard of care and placebo. Resolution of CDAD is defined as the cessation of diarrhea for at least two consecutive days.

200 subjects who met the eligibility criteria and signed the informed consent and received standard of care treatment were randomized 1:1 treatment allocation to receive study treatment: 101 subjects in the GS-CDA1/MDX-1388 (Monoclonal antibody (Mab)) treatment group and 99 subjects in the placebo treatment group

Determine if the addition of a C. difficile toxin A human monoclonal antibody combined with C. difficile toxin B human monoclonal antibody to standard of care treatment reduces the number of patients who experience standard of care treatment failure compared to those patients receiving standard of care and placebo. Standard of care treatment failure is defined as (i) recurrence of diarrhea (after it had initially resolved) while on SOC treatment during the first 14 days, or (ii) change in SOC treatment (i.e., antibiotics given), or (iii) diarrhea episode lasting ≥14 days while on SOC treatment.

200 subjects who met the eligibility criteria and signed the informed consent and received standard of care treatment were randomized 1:1 treatment allocation to receive study treatment: 101 subjects in the GS-CDA1/MDX-1388 (Monoclonal antibody (Mab)) treatment group and 99 subjects in the placebo treatment group

Determine if the addition of a C. difficile toxin A human monoclonal antibody combined with C. difficile toxin B human monoclonal antibody to standard of care treatment reduces the number of patients with severe C. difficile disease compared to those patients receiving standard of care and placebo. Severe initial disease is defined as ≥ 5 unformed stools/day for 2 consecutive days from day 1 to the end of the initial episode of diarrhea and discontinuation of SOC.

200 subjects who met the eligibility criteria and signed the informed consent randomized to receive study treatment: 101 in the GS-CDA1 and MDX-1388 (Monoclonal antibody (Mab)) treatment group and 99 in the placebo treatment group.

Antibody concentrations to Toxin A and to Toxin B in those patients receiving C. difficile toxin A human monoclonal antibody combined with C. difficile toxin B human monoclonal antibody and standard of care treatment to those patients receiving standard of care and placebo

200 subjects who met the eligibility criteria and signed the informed consent randomized to receive study treatment: 101 in the GS-CDA1 and MDX-1388 (Monoclonal antibody (Mab)) treatment group and 99 in the placebo treatment group.