Interhospital Transfer Networks as a Measure of Hospital Resilience Under Strain

Introduction: During the COVID-19 pandemic many hospitals experienced a surge in demand that outstripped their resources and resulted in adverse patient outcomes. An ability to easily transfer patients to other hospitals may be an important determinant of hospital resilience while under strain. We used network analyses to quantify hospital-level variation in the number of transfer partners as a potential measure of hospital resilience.


Methods: We performed a retrospective study using 2019 Healthcare Cost and Utilization Project all-payer claims data from adult acute care hospitals in Florida, Iowa, Maryland, Nebraska, and Wisconsin. We included all adult ED and inpatient encounters. We defined interhospital transfers as instances in which a patient received care at two different hospitals on the same day or the subsequent day. For each hospital we calculated three measures of transfer partnerships within their Pittsburgh Atlas Region: network out-degree, transfer instability index (TII), and inverse Herfindahl-Hirschman Index (iHHI). We examined the relationship between these variables and their association with hospital characteristics obtained from the 2019 AHA annual survey.


Results: We identified 196,174 interhospital transfers across 569 hospitals. The median number of outgoing transfers per hospital was 265 [IQR: 121 - 494]. All three measures varied extensively across hospitals: median [IQR] for out-degree = 6 [4 – 10]; TII = 3.2 [2.0 – 4.9]; and iHHI = 2.5 [1.7 – 3.6]. These measures were highly correlated: r for out-degree and TII = 0.86; for out-degree and iHHI = 0.73; and for TII and iHHI = 0.97. Using iHHI as the primary measure of effective transfer partnerships, a greater iHHI was associated with teaching hospitals (vs. non-teaching), larger hospitals (vs. smaller), and being in an urban area (vs. other). Extensive variation was observed even within these categories.


Conclusions: Hospitals vary widely in their number of transfer partners, with large hospitals, teaching hospitals, and urban hospitals having more transfer partners when compared to their counterparts. Future work should examine whether the number of transfer partners is associated with hospital resilience under strain and identify ways to diversify the number of transfer partners as a strategy to handle future surges in demand.