University of Michigan, RAND study explores link between hospital occupancy, infection rates

Patient and nurse in hospital
A new study from researchers at the University of Michigan and RAND Corporation dives into the relationship between hospital occupancy and infection risk. (Getty/monkeybusinessimages)

It stands to reason that the fuller an inpatient ward is, the greater a patient's risk of infection—but a new study from the University of Michigan and RAND Corporation suggests that isn't true.

In a study of more than 550,000 patient discharges from 327 California hospitals, researchers found that patients were most likely to contract Clostridium difficile—a stubborn and potentially deadly hospital-borne infection—when inpatient wards were in the "middle range" of capacity, or between 25% and 75% full.

Patients admitted to a unit that was at between 25% and 75% capacity were three times more likely to contract C. diff compared to those in units at below 25% or above 75% capacity, according to the study.

"Our hypothesis going in was essentially that when hospitals are busier, perhaps care quality is compromised," Mahshid Abir, M.D., assistant professor of emergency medicine at UM Medical School and the study's lead author, told FierceHealthcare. "Certainly when we saw these findings, we were surprised."

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Overall, more than 2,000 patients included in the study, which looked at discharges between 2008 and 2012, contracted C. diff during their hospital stay. Hospitals often struggle to control C. diff infections, and a significant number of readmissions can be linked to such infections.

By basing the study around a model that accounts for seasonal staffing changes or unit closure, for example, researchers were better able to filter out infections that a patient had before arriving at the hospital, she said. Calculating occupancy in this way could also help providers identify potential risk factor for infection, according to the study.

The researchers defined occupancy as how many beds a hospital actually has available and staffed, not how many it is licensed to operate. This model, Abir said, could be adapted to track how other patient outcomes intersect with occupancy, as it is more precise.

The model, she said, is "one of the most important contributions" of the study.

Abir said that further study is needed to dig more into the relationship between inpatient occupancy and infection rates as, for example, certain protocols may be changed or triggered when a unit is at low or high occupancy.

"What happens when we're at our average? Do we get more complacent? Are there policies that change when they get really busy?" Abir said. "So there's a lot that we need to understand."

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UM and RAND's research on the intersection between occupancy and infection control comes as Leapfrog Group finds that the number of hospitals reaching zero infections for certain hospital-acquired conditions is backsliding.

An analysis of Leapfrog's Hospital Safety Survey data found that in 2017, about 13% of the nearly 2,000 hospitals in the survey reported no central-line associated bloodstream infections. That's down from 25% in 2015, according to the report.

Infection control programs require significant resources and may especially pose a challenge to rural and smaller facilities, research suggests.