The study, published Oct. 1, 2026 in the journal Infection Control and Hospital Epidemiology, combined six months of intensive patient surveillance with a sophisticated computational model of two leukemia and hematopoietic cell transplant units in a large US tertiary care hospital. The central finding is stark: patients who were visibly sick with C. difficile infection were not the main engine of new cases. Instead, patients who carried the bacterium silently, without any clinical signs, were responsible for the overwhelming majority of transmissions that produced new colonizations. According to the model, asymptomatic colonized patients accounted for 92 percent of transmission events that resulted in new colonized individuals on the units.

C. difficile is one of the most common hospital-acquired infections and a leading cause of healthcare-associated diarrhea. It thrives when the gut microbiome has been disrupted, typically by antibiotics, and it spreads through spores that can persist on surfaces and equipment for months. For cancer patients, particularly those undergoing treatment for blood malignancies or recovering from hematopoietic cell transplants, the stakes are exceptionally high. These patients have among the highest incidences of C. difficile infection of any hospital population, and a secondary infection on top of immunosuppressive therapy can be fatal.

“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.”

The challenge the team faced is one that has long frustrated infection-control researchers: transmission is invisible. Standard clinical practice tests patients for C. difficile only when they show symptoms such as diarrhea, which means that people who carry the bacterium without signs of illness slip through undetected. A positive or negative test result on a given day is a snapshot, not a story, and it says nothing about who infected whom. “Testing data only provides a snapshot – are you positive or negative on a given day and time – but transmission events are invisible,” Lanzas explains. “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.”

To make the invisible visible, the researchers built a stochastic, individual-based network model, a type of simulation that tracks every patient, every room and every healthcare worker connection on the two units. Rather than averaging over a population, the model simulated each individual’s state, whether uncolonized, asymptomatically colonized or actively infected, and updated those states over time based on the contact structure of the ward. Healthcare worker room assignments provided the backbone of the network, defining which patients were potentially linked through shared staff, equipment and physical space. Key parameters of the model were estimated using a statistical technique called particle filtering, which iteratively adjusts the simulation until its outputs match the observed data as closely as possible.

The data used to calibrate the model came from an unusually thorough surveillance program. Collaborators at Washington University School of Medicine collected cultures and nucleic acid amplification testing, or NAAT, from patients both at admission and weekly throughout their stay, regardless of whether symptoms were present. Toxin enzyme immunoassay tests were used to diagnose active C. difficile infection. This active surveillance, testing everyone whether sick or not, is what allowed the researchers to distinguish between patients who were merely colonized and those with clinical disease, a distinction that routine testing cannot make.

The model’s output was revealing in several ways. First, it showed that routine, symptom-driven testing alone captures only 23 percent of patients carrying C. difficile, leaving the vast majority of carriers undetected. Second, it quantified the origins of new colonization events: 51 percent of new colonizations, with a range of 38 to 70 percent across model runs, were due to importation, meaning the patients arrived at the unit already carrying the bacterium. Strikingly, 87 percent of those imported cases were admitted as asymptomatic carriers, not as diagnosed infections. The remaining 49 percent of new colonizations, ranging from 30 to 62 percent, arose from transmission within the unit itself, and asymptomatic colonized patients were the source in 92 percent of those transmissions.

Perhaps the most encouraging implication concerns patients with active, symptomatic infections. The model indicated that infection control measures focused on diagnosed CDI patients, such as isolation and contact precautions, appear to be working: symptomatic patients contributed relatively little to onward transmission. The problem lies elsewhere, in the silent reservoir of carriers who are never isolated, never flagged and never treated, because nobody knows they carry the organism. These findings reinforce the role of asymptomatic colonization, particularly through admission importation, in sustaining C. difficile transmission in high-risk hospital settings.

“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.” The researchers hope the modeling framework can be adapted to other pathogens, helping hospitals identify the specific contact points where infection risk is highest and design targeted interventions for the patients who need them most. In wards where the population is uniquely vulnerable, knowing where an outbreak will come from before it starts may prove as valuable as any drug.

Subject of Research: Transmission dynamics of Clostridioides difficile in hospital oncology units

Article Title: Model traces C. diff spread in hospital oncology units

Article References: Model traces C. diff spread in hospital oncology units. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: Clostridioides difficile, hospital-acquired infection, oncology, asymptomatic colonization, transmission modeling, infection control, immunocompromised patients, stochastic simulation, healthcare epidemiology, leukemia, stem cell transplant, antimicrobial resistance

The core of the concern raised by APIC and SHEA is operational rather than abstract. Infection preventionists and healthcare epidemiologists working on the front lines of American medicine depend daily on the CDC’s science, surveillance systems, and guidance documents to make decisions that protect both patients and healthcare personnel. When a hospital investigates a cluster of healthcare-associated infections, when a nursing home must respond to an outbreak of a respiratory pathogen, or when an outpatient clinic needs to update its vaccination protocols, the technical foundation for those decisions typically originates at the federal agency. According to the joint statement, that foundation is visibly weakening: guidance is slower to arrive, technical assistance is harder to reach, and scientific expertise is thinner precisely when it is most needed.

The timing of the reported workforce losses amplifies the risk. Healthcare facilities are entering the respiratory virus season without updated federal vaccine recommendations, a gap that leaves infection prevention teams without the authoritative national benchmarks they have historically relied upon to standardize immunization practices across institutions. At the same time, facilities are preparing for potential measles exposures, a disease that demands rapid identification, isolation, and contact tracing protocols grounded in current epidemiological evidence. The organizations also point to the monitoring of imported threats such as Ebola, which requires sustained laboratory capacity, surveillance infrastructure, and rapid communication channels between federal scientists and local practitioners. Each of these scenarios depends on a functioning national public health partner, and each becomes more hazardous when that partner is operating with a substantially reduced workforce.

Infection prevention is a discipline built on the rapid translation of scientific evidence into bedside practice. Infection preventionists are the specialists who design and enforce the protocols that prevent healthcare-associated infections, which affect millions of patients worldwide each year and represent one of the most common adverse events in medical care. Healthcare epidemiologists complement this work by applying epidemiological methods to detect outbreaks, evaluate antimicrobial resistance patterns, and assess the effectiveness of preventive interventions within healthcare settings. Both professions operate within a distributed network in which local expertise is amplified by national coordination. The CDC functions as the hub of that network, synthesizing data from thousands of facilities, issuing evidence-based recommendations, and providing the laboratory and technical infrastructure that individual institutions cannot replicate on their own.

APIC President Kathy Ward, a registered nurse with advanced credentials in infection control, framed the relationship between frontline practitioners and the federal agency as a partnership that is now under strain. In the statement, she emphasized that infection preventionists safeguard the nation’s healthcare system against healthcare-associated infections and that the profession depends on the CDC to provide timely, evidence-based guidance. She warned that the losses described in the reporting put that partnership, and patient safety itself, at risk. Her comments reflect a practical reality: when federal guidance is delayed or unavailable, individual facilities must improvise, and improvisation in infection control can lead to inconsistent practices, gaps in protection, and ultimately preventable infections.

SHEA President Lisa Maragakis, a physician and epidemiologist, directed her warning toward a longer-term consequence of workforce erosion. In the statement, she observed that healthcare epidemiology is built on sound science and trusted data, and she characterized the CDC’s scientific independence and expert workforce as national assets that cannot be rebuilt overnight once they are lost. This point carries particular technical weight. The scientists who staff the agency’s emerging infectious disease and respiratory disease centers accumulate institutional knowledge, methodological expertise, and operational experience that are not easily transferred or replaced. Experienced federal scientists develop the capacity to recognize early signals of emerging threats, to design surveillance systems that capture meaningful data, and to communicate complex findings to practitioners who need actionable guidance. When such experts depart, their institutional memory departs with them, and rebuilding that capacity requires years of recruitment, training, and mentorship.

The downstream effects of a weakened CDC do not remain contained within the agency. As APIC and SHEA describe it, when the national partner is weakened, the burden shifts to already stretched healthcare facilities and to state and local health departments, many of which have faced their own staffing and funding challenges in recent years. State and local public health agencies depend on federal technical assistance, laboratory confirmation capabilities, and coordinated data systems to carry out their mandates. When federal capacity contracts, these agencies absorb responsibilities they may lack the resources to fulfill, and the resulting gaps propagate outward to patients and communities, who ultimately bear the consequences in the form of increased exposure to preventable infections and slower responses to outbreaks.

In response to the situation, the two organizations have issued a three-part call to action directed at Congress and the Administration. First, they urge the restoration and sustained support of CDC staffing in infectious disease programs, healthcare quality promotion, and laboratory operations, the specific divisions whose expertise underpins infection prevention practice nationwide. Second, they call for the protection of the agency’s scientific independence, reflecting a concern that political interference in scientific processes would further undermine the credibility and reliability of federal guidance. Third, they demand that funds appropriated for state and local public health partners be distributed promptly, ensuring that the frontline agencies responsible for local outbreak response receive the resources that Congress has already allocated. Together, these recommendations address the workforce, the institutional safeguards, and the funding pipelines that the organizations view as the essential infrastructure of national infection prevention capability.

The statement also situates the current moment within a broader understanding of how healthcare safety is produced. The prevention of healthcare-associated infections is not achieved by any single institution acting alone; it is the product of a layered system in which federal science, state and local public health infrastructure, and frontline clinical expertise reinforce one another. Surveillance data collected by the CDC inform the guidelines that infection preventionists implement in their facilities, and the observations of those frontline practitioners in turn feed back into national evidence. Disruption at any layer degrades the entire system, but disruption at the federal layer is particularly consequential because it affects every facility simultaneously. The organizations’ warning suggests that the reported loss of nearly a third of the agency’s workforce represents precisely such a systemic disruption, one whose effects are already observable in delayed guidance and reduced access to technical assistance.

As respiratory virus season proceeds and as facilities continue to prepare for measles exposures and monitor imported threats, the concerns articulated by APIC and SHEA are likely to frame an ongoing policy debate about the nation’s public health readiness. The organizations’ message is that the expertise housed within the CDC constitutes a form of national infrastructure comparable in importance to physical systems, and that its loss carries consequences measured not in budget figures but in patient outcomes. Their statement serves as both a diagnosis of the current strain on the infection prevention community and a formal request to federal policymakers to restore the scientific capacity on which American healthcare safety has long depended. Whether that request translates into legislative and administrative action remains to be seen, but the two societies have made clear that, in their assessment, the window for protecting this critical national asset is narrowing.

Subject of Research: Impact of CDC workforce reductions on infection prevention and healthcare epidemiology

Article Title: APIC and SHEA Statement on reported erosion of CDC capacity

Article References: APIC and SHEA Statement on reported erosion of CDC capacity. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: CDC, APIC, SHEA, infection prevention, healthcare epidemiology, public health workforce, healthcare-associated infections, respiratory virus season, vaccine recommendations, measles, Ebola, health policy