To prevent infections, hospitals rely on chlorhexidine wipes to sterilize patients’ skin before procedures. While that is critically important for the patient, new research suggests chlorhexidine does the opposite for everyone else in the hospital.
Researchers have discovered that traces of chlorhexidine linger on surfaces much longer than previously thought—long enough to help microbes build tolerance. The team also found that chlorhexidine-tolerant bacteria spread throughout the hospital environment not only through touch but also—surprisingly—through the air.
For their study, the Northwestern University team applied chlorhexidine to common materials—plastic, metal and laminate—often found in hospitals. Then, they cleaned the surfaces with chlorhexidine-free disinfectants typically used to sterilize hospital environments.
Even after these cleaning treatments, chlorhexidine residue lingered on surfaces after 24 hours. The residue levels were too low to kill bacteria but high enough to expose them to the chemical. In these conditions, surviving microbes can develop tolerance to the disinfectant.
Under these conditions, the researchers exposed several clinically relevant bacteria, including E.coli, to trace concentrations of chlorhexidine. Even after a full day of exposure, the microbes survived.
Next, Associate Professor Erica Hartmann and her team collected almost 200 samples from hospital bed rails, keyboards, doorsills, light switches and sink drains inside a medical intensive care unit (MICU). From these samples, they isolated more than 1,400 bacteria— and about 36% exhibited some level of tolerance to chlorhexidine.
While bacteria were found all over the MICU, sink drains stood out. Compared with dry surfaces, drains contained far higher levels of bacteria, including strains capable of tolerating much higher concentrations of chlorhexidine. This matches previous studies that have found hospital sinks to be bacteria hotspots. For example, in 2017, a medical center in Japan traced an outbreak of the multidrug-resistant bacteria Carbapenemase-producing Enterobacterales (CPE) to the facility’s sinks. Even after replacing all the sinks in the pediatric ward, the contamination continued until intense infection protocols were finally able to halt it.
But perhaps the most surprising—and worrying—discovery is that Hartmann and her team found bacteria with signs of chlorhexidine tolerance in samples collected from the top of doorsills.
As people rarely touch the tops of doors, the assumption is that the bacteria hitched a ride on airborne particles, like dead skin cells.
“Our original hypothesis was that we’d find evidence of chlorhexidine in high-touch areas like light switches. We included doorsills as a negative control,” said Hartmann. “The point is not that we need to clean our doorsills. The point is that we need to think about airflow pathways as a potential route of exposure or microbe transport within a built environment. Every time we walk around, we shed microbes, skin and chemicals that are on our skin. Some of that potentially floats around and deposits elsewhere in the room.”