The Asymptomatic C difficile Carrier: What to Do

Erik R. Dubberke, MD, MSPH; Jennie H. Kwon, DO, MSCI


November 04, 2016

Screening and Isolating Asymptomatic Clostridium difficile Carriers

The epidemiology of Clostridium difficile infection (CDI) indicates that the asymptomatic C difficile carrier plays an important role in transmission of this organism in the hospital setting, leading to new cases of CDI. A recent study[1] examined the impact of isolating asymptomatic C difficile carriers on CDI incidence, but many questions remain.

Longtin and colleagues[1] conducted a quasi-experimental study from November 2013 to March 2015 in a hospital in Quebec. In November 2013, patients admitted through the emergency department with an expected length of stay > 24 hours were screened for C difficile carriage by polymerase chain reaction (PCR). Testing was conducted once daily, 7 days a week.

Patients who screened positive for C difficile were placed into modified contact precautions. The incidence of healthcare-associated CDI (HA-CDI), as well as the CDI incidence at other hospitals in Quebec, was calculated before and after the intervention. The primary outcome was the incidence of HA-CDI per 4-week period, by segmented regression analysis and autoregressive integrated moving average (ARIMA) modeling.

Evidence of CDI Prevention

Of 8218 eligible patients, 7599 (92.5%) were screened, of whom 368 (4.8%) were identified as asymptomatic carriers. The HA-CDI incidence after the intervention was 3.0 per 10,000 patient-days, compared with 6.9 per 10,000 patient-days before the intervention (P < .001). There was no immediate change in HA-CDIs on implementation (P = .92), but there was a significant reduction in trend over time of 7% per 4-week period (P = .02).

ARIMA modeling also detected a significant effect of the intervention, represented by a gradual progressive decrease in the HA-CDI time series by an overall magnitude of 7.2 HA-CDIs per 10,000 patient-days. By contrast, no significant reductions in HA-CDI rates occurred in the control groups. The authors estimated that the intervention prevented 62% of expected cases of CDI.

The investigators also found a significant reduction in prescriptions for CDI treatment (metronidazole and oral vancomycin), but a slight increase in overall antimicrobial prescribing and a slight reduction in proton pump inhibitor prescribing after the intervention. There was also a significant increase in hand-hygiene compliance after the intervention (36.6% vs 49.7%; P < .001).

On the basis of a limited sample of C difficile isolates, the proportion of CDI cases due to the NAP1 strain decreased from 59% before the intervention to 20% after the intervention (P = .49) at the study hospital, but not at other hospitals in Quebec.


This is an important study examining a novel approach to CDI prevention. The proportion of estimated CDI cases prevented (62%), is similar to the proportion of cases that may be related to transmission from asymptomatic carriers.[2,3]

However, the study has several limitations. The intervention was conducted at a single hospital, so the findings need to be replicated elsewhere. Also, as a population-level analysis the correlation between the intervention and a reduction in CDI does not equate to causation. Improvements in hand hygiene in the postintervention period were observed, suggesting that compliance with infection control measures improved globally at this institution, unrelated to the intervention.

Furthermore, data on the antimicrobial classes prescribed were not presented. Prescribing of antimicrobials that carry lower risk for CDI may explain the reductions in CDI. Changes in antimicrobial class prescribing may explain the reduction in CDI due to the NAP1 strain observed.

Existing data suggest that PCR detects only 68% of asymptomatic C difficile carriers.[4] In addition, patients admitted to the hospital who did not come through the emergency department were not screened for carriage. This indicates that at least 30% of asymptomatic carriers would have remained undetected. One study estimated that only 20% of HA-CDI cases would be prevented if 75% of carriers were identified.[3]

Most people colonized with C difficile in the hospital setting are asymptomatic carriers. Currently, there are no formal efforts to prevent C difficile transmission from these asymptomatic carriers. The findings of the study by Longtin and colleagues[1] are intriguing, but need to be validated before screening and isolation of asymptomatic carriers becomes a recommended CDI prevention practice.


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