The purpose of this study is to evaluate the efficacy and safety of AZD5148 for prevention of recurrence of Clostridioides difficile infection in Individuals 18 years of age and above.

Approximately 230 participants will be enrolled and randomized 1:1 to receive a single dose of either AZD5148 or placebo (normal saline). Route of administration (intramuscular or intravenous push) will be according to the Investigator's choice. Stratification will be based on geographical region.

Study details include:

• Up to 2 site visits for confirmation of eligibility and dose administration, including stool sample collection;
• Up to 7 planned visits;
• Contacts initiated by site staff -weekly, later monthly follow up;
• Electronic diary completion.

Inclusion Criteria:

Participant must be ≥ 18 years of age at the time of signing the informed consent, capable of giving signed informed consent.

Participants with a qualifying C. difficile infection episode at the time of providing informed consent defined by:

• Positive local C. difficile toxin test (eg, immune assay or CCNA) on an unformed stool sample collected during this episode, and
• Receipt of standard of care antibacterial drug therapy for C. difficile infection (fidaxomicin, vancomycin or metronidazole) for this episode, with planned duration of at least 10 and at most 25 days at time of IMP administration.

Note: Diarrhea is not required to be present on the day of investigational medicinal product (IMP) administration.

Body weight ≥ 40 kg

Exclusion Criteria:

History of inflammatory bowel disease (eg, ulcerative colitis, Crohn's disease, microscopic colitis).

Participant with a non - CDI (C. difficile infection) condition such that the participant routinely passes loose stool (eg, patients with an ostomy)

Planned surgery for C. difficile infection within 24 hours of enrollment

Current toxic megacolon and/or small bowel ileus

Any history of total colectomy or bariatric surgery (bariatric surgery which does not disrupt the gastrointestinal lumen, ie, restrictive procedures such as banding, are permitted).

Major gastrointestinal surgery as assessed by the Investigator (eg, significant bowel resection or diversion) within 90 days before enrollment (this does not include appendectomy or cholecystectomy)

Due to receive more than 25 days of antibacterial drug therapy for C. difficile infection for the qualifying C. difficile infection episode

Treatment with a fecal donor transplant or fecal microbiota product in the 180 days before IMP administration, are receiving or planned administration for the qualifying episode of C. difficile infection, or planned administration during the 180 days after IMP administration

Treatment with bezlotoxumab in the 180 days before IMP administration, are receiving or planned administration for the qualifying episode of CDI, or planned administration during the 180 days after IMP administration.

Qualified researchers can request access to anonymized individual patient-level data from AstraZeneca group of companies sponsored clinical trials via the request portal Vivli.org. All requests will be evaluated as per the AZ disclosure commitment: https://astrazenecagrouptrials.pharmacm.com/ST/Submission/Disclosure.

Yes, indicates that AZ are accepting requests for IPD, but this does not mean all requests will be shared.

AstraZeneca will meet or exceed data availability as per the commitments made to the EFPIA PhRMA Data Sharing Principles. For details of our timelines, please rerefer to our disclosure commitment at https://astrazenecagrouptrials.pharmacm.com/ST/Submission/Disclosure.

When a request has been approved AstraZeneca will provide access to the anonymized individual patient-level data via secure research environment Vivli.org. Signed Data Usage Agreement (non-negotiable contract for data accessors) must be in place before accessing requested information.

Double-blind: Participant, Care Provider, Investigator, Outcomes Assessor