Estimate how importation and within-unit transmission contribute to C difficile colonization and infection in leukemia and hematopoietic cell transplant units, including the roles of asymptomatic colonization (AC) and symptomatic infection (CDI).
Approach:
Study design: Prospective cohort study in two leukemia and hematopoietic cell transplant units from January 19 to July 22, 2019; 384 of 421 admitted patients consented to testing.
Testing and modeling: Researchers collected stool samples and rectal swabs at enrollment and weekly, and used clinically indicated toxin testing to identify CDI. They combined test results with patient movements, room assignments, staffing patterns, and environmental sampling in a …
Key Findings:
Across 1,000 model simulations, 51% of new colonizations were attributed to importation and 49% to within-unit transmission.
Among imported colonizations, 87% involved patients admitted with AC. Patients with AC were modeled as the source of 92% of transmission events leading to new colonization; CDI contributed relatively little.
The 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 testing approach.
For new CDI cases, 87% were attributed to importation. Among within-unit transmission events resulting in CDI, patients with AC were the modeled source in 92% of cases.
Model estimates were weakly constrained by the available data; source attribution was calibrated using 18 CDI cases and 85 AC cases.
Interpretation:
The authors reported that asymptomatic colonization, including colonization present at admission, may contribute substantially to C difficile acquisition in these high-risk units. They noted that targeting AC may be difficult because it often went undetected and most modeled AC patients did not progress to CDI.
Limitations:
The study was conducted at one health care facility, which may limit generalizability.
The contact network recorded shared health care workers but not the frequency, identity, or duration of staff room visits.
Transmission from family members and visitors was not included, potentially biasing the model toward overestimating importation.
The small number of cases used for source attribution produced wide ranges and left estimates weakly constrained.
Conclusion:
The authors stated that interventions targeting AC could reduce CDI by reducing onward transmission from AC or progression from AC to CDI.
