Model tracks invisible C. diff transmission in hospital cancer units

In a new study, researchers modeled the transmission of Clostridioides difficile (C. diff) infections among patients in hospital cancer units. They found that most new infections were introduced by patients who were infected but not symptomatic at the time of admission, rather than by patients who were infected and symptomatic. The model provides a clearer picture of C. diff transmission events in oncology wards and could help inform protocols aimed at preventing future disease transmission in a highly susceptible population.

Cancer treatments, while increasingly effective, leave their recipients immunocompromised and at greater risk of contracting infection than the general population. Hospital-acquired infections can cause severe complications in cancer patients, and C. diff is one of the most common.

"Physicians have singled out antimicrobial resistance as a big issue for improvement in cancer patients," says Cristina Lanzas, professor of infectious disease at North Carolina State University's College of Veterinary Medicine and corresponding author of the research.

"The cancer treatments are improved, but the secondary infections patients get because they are so immunocompromised can be fatal. We decided to look at how C. diff infections were transmitted in oncology wards."

Generally speaking, clinicians test patients for C. diff only when they have clinical signs; however, patients can also carry this pathogen in the gut without symptoms and may contribute to its transmission.

The researchers combined six months of active patient surveillance (testing patients for C. diff regardless of clinical signs) with a simulation model of every room, patient and staff connection on two cancer units. The data was provided by collaborators at Washington University School of Medicine.

Testing data only provides a snapshot – are you positive or negative on a given day and time – but transmission events are invisible. We developed models that traced potential transmission routes and then looked at each model's ability to replicate actual infection data. Then we chose the model that aligned best with the data we had."

Cristina Lanzas, professor of infectious disease, North Carolina State University's College of Veterinary Medicine

According to the model, testing alone only captures 23% of patients carrying C. diff.

The modeling also revealed that patients with active C. diff infections were not the main source of new colonization. Rather, asymptomatic colonized (AC) patients – people who carry C. diff but don't have clinical signs – were responsible for 92% of transmissions that resulted in new colonizations.

The researchers hope that their model could be applied to different pathogens to help clinicians and hospitals identify contact points where risks for infections are increased.

"The issue of people carrying pathogens without knowing about it is very common with all antimicrobial resistant pathogens – we can really be our own worst enemies," Lanzas says. "But by modeling these events, we can make the invisible visible, and perhaps that can lead to new protocols for patients coming into these wards."