Colonization Amplification Despite Limited In-Hospital Transmission: A Modeling Study

• The authors employ a compartmental modeling approach to quantify in-hospital spread of Clostridioides difficile and the hospital’s role in community colonization.
• The analysis uses data from UCSF Medical Center to parameterize dynamics among symptomatic and asymptomatic patients.
• Two key metrics are emphasized: the intrinsic reproduction number (R i) for in-hospital transmission and a colonization amplification index (A i), defined as the ratio of colonized patients at discharge to those admitted.

• Across simulations, the median in-hospital reproduction number was 0.61, with a plausible range indicating limited sustained transmission within the hospital setting.
• In contrast, the amplification of colonization during hospitalization was substantial, with a median A i of 1.9, signaling more colonization accrued by discharge than existed at admission.
• Sensitivity analyses show amplification persists under a variety of scenarios; however, R i can exceed 1 when certain boundary conditions are met, such as low admission colonization prevalence, a low progression rate from colonization to symptomatic disease, or prolonged incubation periods.

• Redefining healthcare-associated CDI by shifting to thresholds of ≥1 day post-admission (instead of >3 days) raises A i by 11% and increases R i by 21%, reflecting how case-definition boundaries influence transmission and colonization estimates.
• Conversely, using a ≥5 days post-admission threshold slightly lowers these metrics (A i by 5% and R i by 8%).

• Strategies directed at asymptomatic carriers—through contact precautions and/or prophylactic treatment—demonstrated reductions in both A i and the incidence of CDI.
• Combined interventions produced the largest reductions, surpassing the effect of contact precautions implemented alone.
• These results point to asymptomatic carriage as a potentially important, modifiable contributor to overall transmission burden.

• The main limitations arise from uncertainty in several natural-history parameters, notably colonization prevalence at admission, the rate of progression from colonization to symptomatic disease, and the incubation period.
• Because these factors influence model outputs, the authors emphasize interpretation within the bounds of sensitivity analyses.

difficile appears limited (R i generally below 1), yet the hospital environment may still substantially amplify colonization, thereby feeding community transmission.

difficile burden.

• The overarching conclusion is that in many scenarios, in-hospital transmission of C.
• The study advocates expanding metrics beyond R i alone to capture the hospital’s contribution to the total C.
• Practical implications highlighted include the potential value of addressing colonization dynamics at admission and possibly at discharge, and prioritizing interventions that target asymptomatic carriers to mitigate transmission and reduce disease burden.

• The authors acknowledge uncertainty surrounding key parameters and emphasize that amplification effects can persist or intensify under certain parameter bounds.