How Multidrug-Resistant Organisms Spread in Nursing Homes: New Study Highlights Everyday Risks

Researchers followed 197 newly admitted residents at three VA nursing homes in Michigan and Ohio between April 2021 and September 2023. The goal was to track how often MDROs—such as MRSA (methicillin-resistant Staphylococcus aureus), VRE (vancomycin-resistant enterococci), and resistant gram-negative bacilli (RGNB)—are carried by residents and whether they spread through the environment and interactions with staff and equipment.

"These in-depth studies are hard to conduct but very important to ultimately develop interventions and strategies for improvement,"  said Dr. Lona Mody, lead author of the study. "We now establish a novel framework to understand transmission, outline resources that are required and the expertise it takes." 

At the time of nursing home admission, more than one-third of residents (36.5%) were already colonized with at least one MDRO. The most common was VRE, followed by RGNB and MRSA. Nearly 40% of resident rooms had at least one surface contaminated with one of these organisms, most often the bedrail, bed control, or privacy curtain.

Of the 182 residents who had at least one follow-up visit, 65.4% were found to be colonized with an MDRO at some point during their stay. Among those who were not colonized at baseline, 40.9% acquired a new MDRO while in the nursing home. On average, it took just under 15 days for a resident to acquire one of these organisms. VRE was the most frequently acquired, followed by RGNB and MRSA.

The study also looked closely at 345 out-of-room “interactive visits”—times when residents left their rooms for therapy, meals, dialysis, or other appointments. During these visits, researchers collected swabs from resident hands, healthcare workers, and surfaces they touched to check for bacteria.

MDRO transmission occurred in 55 of those 345 visits (16%). Most of these events were seen during therapy sessions, but some occurred during dialysis, radiology, or dining visits as well. Hands and equipment were often involved in the spread.

Resident hands were a frequent source of transmission. When a resident’s hands were colonized with VRE, 44% of the time they spread the bacteria to surfaces they touched. In contrast, when a surface was contaminated beforehand, it led to hand contamination only about 6% of the time.

To confirm how bacteria spread, the researchers used whole genome sequencing to match the genetic fingerprint of the bacteria collected. In all cases where a source was suspected based on simple lab tests, the DNA confirmed a match between the source and where it ended up—usually from a resident’s hand to a shared surface. Even when no clear source was found during the visit, sequencing was able to trace the bacteria to the resident or their room from an earlier time in two-thirds of cases.

"Our genomic data shows that resident hands are an important source of transmission. Our policies generally focus on healthcare providers and front-line personnel. We really should engage our patients as partners in infection prevention," Dr. Mody explained. "Aligning clinical epidemiologic data with genomic work is a very exciting since similar approaches can be used to answer many other difficult questions."

The study also found that residents with longer hospital stays before entering the nursing home and those who had taken antibiotics recently were more likely to be colonized at baseline. Those who stayed longer in the facility were more likely to pick up a new MDRO during their time there.

Colonization was not always permanent. About 37% of residents who had an MDRO at admission were no longer colonized at discharge. On the other hand, 20% of residents who started out without any MDROs left the facility colonized with one.

Although the three nursing homes had some differences in resident characteristics and baseline contamination rates, the study found no major differences in how often MDROs were acquired or transmitted between them.

This study is one of the most detailed looks to date at how MDROs spread during common out-of-room activities in VA nursing homes. Researchers collected thousands of samples over 6,400 days of resident observation. Their findings point to the importance of paying attention to shared spaces and resident movement, not just what's happening inside individual rooms.