The Association of Inpatient Occupancy with Hospital-Acquired Clostridium difficile Infection
Few studies have evaluated the relationship between high hospital occupancy and hospital-acquired complications. We evaluated the association between inpatient occupancy and hospital-acquired Clostridium difficile infection (CDI) using a novel measure of hospital occupancy. We analyzed administrative data from California hospitals from 2008–2012 for Medicare recipients aged ≥65 years with a discharge diagnosis of acute myocardial infarction, heart failure, or pneumonia. Using daily census data, we constructed patient-level measures of occupancy on admission day and average occupancy during hospitalization (range: 0-1), which were split into 4 groups. We used logistic regression with cluster standard errors to estimate the adjusted and unadjusted relationship of occupancy with hospital-acquired CDI. Across 327 hospitals, 558,344 discharges met our inclusion criteria. Higher admission day occupancy was associated with significantly lower adjusted likelihood of CDI. Compared to the 0-0.25 occupancy group, patients admitted on a day of 0.51-0.75 occupancy had 0.86 odds of CDI (95% CI 0.75-0.98). The 0.76-1.00 admission occupancy group had 0.87 odds of CDI (95% CI 0.75-1.01). With regard to average occupancy, intermediate levels of occupancy 0.26-0.50 (odds ratio [OR] = 3.04, 95% CI 2.33-3.96) and 0.51-0.75 (OR = 3.28, 95% CI 2.51-4.28) had over 3-fold increased adjusted odds of CDI relative to the low occupancy group; the high occupancy group did not have significantly different odds of CDI compared to the low occupancy group (OR = 0.96, 95% CI 0.70-1.31). These findings should prompt exploration of how hospitals react to occupancy changes and how those care processes translate into hospital-acquired complications in order to inform best practices.
© 2018 Society of Hospital Medicine
High hospital occupancy is a fundamental challenge faced by healthcare systems in the United States.1-3 However, few studies have examined the effect of high occupancy on outcomes in the inpatient setting,4-9 and these showed mixed results. Hospital-acquired conditions (HACs), such as Clostridium difficile infection (CDI), are quality indicators for inpatient care and part of the Centers for Medicare and Medicaid Services’ Hospital-Acquired Conditions Reductions Program.10-12 However, few studies—largely conducted outside of the US—have evaluated the association between inpatient occupancy and HACs. These studies showed increasing hospital-acquired infection rates with increasing occupancy.13-15 Past studies of hospital occupancy have relied on annual average licensed bed counts, which are not a reliable measure of available and staffed beds and do not account for variations in patient volume and bed supply.16 Using a novel measure of inpatient occupancy, we tested the hypothesis that increasing inpatient occupancy is associated with a greater likelihood of CDI.
METHODS
We performed a retrospective analysis of administrative data from non-federal, acute care hospitals in California during 2008–2012 using the Office of Statewide Health Planning and Development (OSHPD) Patient Discharge Data set, a complete census of all CA licensed general acute care hospital discharge records. This study was approved by the OSHPD Committee for the Protection of Human Subjects and was deemed exempt by our institution’s Institutional Review Board.
Selection of Participants
The study population consisted of fee-for-service Medicare enrollees ≥65 years admitted through the emergency department (ED) with a hospital length of stay (HLOS) <50 days and a primary discharge diagnosis of acute myocardial infarction (MI), pneumonia (PNA), or heart failure (HF; [identified through the respective Clinical Classification Software [CCS]).
The sample was restricted to discharges with a HLOS of <50 days, because those with longer HLOS (0.01% of study sample) were likely different in ways that may bias our findings (eg, they will likely be sicker). We limited our study to admissions through the ED to reduce potential selection bias by excluding elective admissions and hospital-to-hospital transfers, which are likely dependent on occupancy. MI, HF, and PNA diagnoses were selected because they are prevalent and have high inpatient mortality, allowing us to examine the effect of occupancy on some of the sickest inpatients.17
Hospital-acquired cases of CDI were identified as discharges (using ICD-9 code 008.45 for CDI) that were not marked as present-on-admission (POA) using the method described by Zhan et al.18 To avoid small facility outlying effects, we included hospitals that had 100 or more MI, HF, and PNA discharges that met the inclusion criteria over the study years.
OSHPD inpatient data were combined with OSHPD hospital annual financial data that contain hospital-level variables including ownership (City/County, District, Investor, and Non-Profit), geography (based on health services area), teaching status, urbanicity, and size based on the number of average annual licensed beds. If characteristics were not available for a given hospital for 1 or more years, the information from the closest available year was used for that hospital (replacement required for 10,504 (1.5%) cases; 4,856 otherwise eligible cases (0.7%) were dropped because the hospital was not included in the annual financial data for any year. Approximately 0.2% of records had invalid values for disposition, payer, or admission route, and were therefore dropped. Patient residence zip code-level socioeconomic status was measured using the percentage of families living below the poverty line, median family income, and the percentage of individuals with less than a high school degree among those aged ≥ 25 years19; these measures were divided into 3 groups (bottom quartile, top quartile, and middle 50%) for analysis.
