A new mathematical model highlights the challenges of preventing Clostridioides difficile transmission in the hospital.
Frequently touched surfaces and objects account for three-quarters of colonizations of patients with Clostridioides difficile in hospital wards, even though those surfaces receive additional cleaning compared to low-touch surfaces.
More than 223,000 hospitalized people are believed to be infected with C difficile each year in the United States, and nearly 13,000 people die from such infections. Corresponding author Cara Joy Sulyok, of the University of Tennessee Knoxville, and colleagues noted that the CDC has labeled C difficile an “urgent public threat” requiring immediate public health action.
C difficile spread can be difficult to stop for a number of reasons. Some patients are asymptomatic, and C difficile spores can survive on objects or surfaces, called “fomites,” for long periods of time. The CDC recommends daily cleaning in the rooms of infected patients, and disinfection of infected-patient rooms upon discharge using a chlorine-based agent.
However, Sulyok and colleagues noted hospitals do not always fully comply with these recommendations, in part over fear that chlorine could damage equipment. Thus, fomites can be a constant potential source of C difficile transmission.
“This raises the question of what type of fomite in a healthcare setting contributes more to the transmission of C difficile infection, fomites that are handled more frequently and tend to be cleaned and disinfected more often, or those that are handled less frequently and tend to be cleaned and disinfected less often,” Sulyok and colleagues wrote.
In an effort to find out, the investigators developed a model that looked specifically at potential contributions of fomites. They split fomites into 2 types: those that were frequently touched, and therefore theoretically cleaned more often, and those that were low-touch, and therefore cleaned less. Surfaces like bed rails, doorknobs, sinks, and tray tables are examples of high-touch fomites, and curtains, furniture, and trash cans are examples of low-touch surfaces, Sulyok and colleagues said.
The model was designed to calculate the relative contributions of the two types of surfaces, with simulations based on a number of variables and scenarios based on a typical hospital setting.
“In most scenarios on average 21%–25% of colonized cases were due to contact with low-touch fomites, while 75%–79% were due to contact with high-touch fomites, despite the extra cleaning of high-touch fomites,” the authors found.
Alternate scenarios suggested that the more high-touch fomites are touched, the more they contribute to the risk of infection.
Notably, when the authors created a scenario in which cleaning and disinfecting protocols were followed near perfectly, the number of cases did not change as much as might be expected.
“Since the average incidence of colonized and diseased individuals did not significantly decrease in this scenario, it implies that increasing the effectiveness of disinfecting and cleaning alone may not be sufficient to control an outbreak of C difficile in a hospital ward,” Sulyok and colleagues said.
Still, the investigators said cleaning and disinfecting high-touch fomites, and reducing contact with them, remains an important strategy, since the near-perfect compliance scenario was one of few that could reduce the incidence of colonized individuals in an outbreak.
The variable that made the biggest difference in terms of the number of colonized patients, though, was the rate at which colonized individuals with insufficient immune responses developed symptoms. The investigators noted that such patients typically would not be tested for C difficile unless or until they became symptomatic.
“Testing for asymptomatic individuals could help to reduce this rate (of transmission), and thus reduce the incidence of diseased individuals, if testing is followed up by antibiotic stewardship practices,” they said.
Other testing strategies suggested by the findings include increasing the effectiveness of post-discharge disinfection, increasing cleaning of high-touch fomites, antibiotic stewardship, and shortening the duration of patient stays in the hospital.
However, Sulyok and colleagues said one major takeaway is that more research needs to be done to understand the role of environmental pathways in C difficile transmission.
Sulyok CJ, Fox L, Ritchie H, Lanzas C, Lenhart S, Day J. Mathematically modeling the effect of touch frequency on the environmental transmission of Clostridioides difficile in healthcare settings. Math Biosci. Published online ahead of print, July 24, 2021. doi:10.1016/j.mbs.2021.108666