Clinical Report: Asymptomatic carriage may fuel C difficile spread

Overview

In a prospective cohort of patients in two leukemia and hematopoietic cell transplant units, a stochastic network model attributed nearly half of new C difficile colonizations to within-unit transmission and most transmission events to asymptomatically colonized patients. The model estimated substantially more acquisition events than routine testing detected; estimates were limited by sparse case data and the single-facility setting.

Background

Clostridioides difficile colonization can occur without symptoms, whereas CDI refers to symptomatic infection. Distinguishing these states matters when assessing how the organism is introduced and transmitted in high-risk oncology units. The study combined serial patient testing with room, staffing, and environmental data in a model designed to account for acquisition events missed by the testing schedule. The supplied context notes that guidance on identifying asymptomatic carriers remains setting-dependent and that evidence is limited.

Data Highlights

Key Findings

• Among 384 consenting patients, stool samples and rectal swabs were collected at enrollment and weekly until discharge; clinically indicated toxin enzyme immunoassay testing was used to identify CDI.
• Across 1,000 simulations, the model attributed 51% of new colonizations to importation and 49% to within-unit transmission.
• Patients modeled as asymptomatically colonized accounted for 87% of imported colonizations and were the modeled source of 92% of transmission events resulting in new colonization.
• The transmission model estimated 3.9 new colonizations per week, compared with 0.9 identified by the observation model, indicating that many acquisition events were not detected by the study testing approach.
• When analysis was restricted to new CDI cases, 87% were attributed to importation; 76% of imported cases involved patients admitted with CDI, while the remainder involved patients admitted as AC who later progressed to CDI.
• Model estimates were weakly constrained by testing data from 18 CDI cases and 85 AC cases. The study was conducted at one facility, and its contact network did not capture staff entry frequency, individual staff contacts, contact duration, or transmission from visitors and family members.

Clinical Implications

The study authors state that interventions targeting AC could reduce CDI by reducing onward transmission from AC or progression from AC to CDI, while noting that colonization often went undetected and most modeled AC patients did not progress to CDI. The supplied CDC guidance describes evaluating and testing asymptomatic high-risk patients as a supplemental measure during outbreaks or when prevention goals are unmet, isolating those who test positive, and not treating in the absence of symptoms.

Conclusion

In these oncology units, the model attributed most within-unit transmission leading to new colonization to asymptomatically colonized patients, while symptomatic CDI contributed relatively little. The estimates warrant cautious interpretation because of limited case data, undetected acquisition, and the single-facility design.

Related Resources & Content

1. Curtis S, et al., Infection Control & Hospital Epidemiology, 2026 — Quantifying the contributions of asymptomatic and symptomatic colonized patients to Clostridioides difficile acquisition in oncological units
2. CDC, 2026 — Clinical Guidance for C. diff Infection Prevention in Acute Care Facilities
3. ASCO Publications, 2016 — Clostridium difficile carriage and its implications in preoperative colorectal cancer patients
4. ASCO Publications — Clostridium difficile carriage and its implications in preoperative colorectal cancer patients.
5. the analytical scientist — C. difficile, But Not Impossible
6. the pathologist — C. difficile, But Not Impossible
7. Quantifying the contributions of asymptomatic and symptomatic colonized patients to Clostridioides difficile acquisition in oncological units
8. Clinical Guidance for C. diff Infection Prevention in Acute Care Facilities
9. https://gutpathogens.biomedcentral.com/counter/pdf/10.1186/s13099-024-00674-0.pdf