Lead author Mahshid Abir, M.D., M.Sc., of U-M and RAND notes that the new approach to measuring hospital occupancy takes into account how many beds the hospital actually has open and staffed, rather than how many they're licensed to operate.
This more precise approach, calculated by looking at census data for each hospital, could be used to track many kinds of patient outcomes in relation to occupancy. The researchers approximated the hospital's actual bed capacity by looking at the maximum daily census in a four-month period around each day that they examined. This allowed them to factor in changes in bed availability, for instance when hospitals close units or have lighter staffing due to seasonal variation.
The team broke occupancy into four levels: low (0 to 25 percent), two classes of moderate (25 percent to 50 percent and 51 percent to 75 percent), and high (76 percent to completely full).
Abir and her colleagues note that other studies in Europe and beyond have shown a higher rate of HAIs when hospitals are very full - but those studies used licensed bed counts and did not factor out infections that the patient already had when they got to the hospital.
"Our initial results indicate a complex relationship between hospital occupancy and outcomes, and merit further evaluation," including analysis of hospital protocols that might be triggered or modified when a hospital is in high or low occupancy, says Abir.
She and her co-authors call for collection of hospital occupancy data by infection control officers, so that more precise measurements of occupancy can be used when examining hospital acquired infections and other preventable threats to patient health and safety.
"The theory that infection rates will go up with occupancy, because of staff cutting corners with steps like handwashing, may seem logical but this model shows it's not as simple as that," says Abir, who leads the U-M Acute Care Research Unit and is a member of the U-M Institute for Healthcare Policy and Innovation. "The impacts of emergency department crowding on patient outcomes have been studied extensively, but the effects of occupancy levels on inpatients has been neglected - despite the fact that a crowded ED is often a function of high inpatient occupancy. Some hospitals may be implementing operational factors during high occupancy that improve HAIs; we need to study what those are."
The team is also looking at the connection between hospital occupancy and patient mortality, and other outcomes, as well as the impact of the California nurse staffing ratio requirements.
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