Quantifying interhospital patient sharing as a mechanism for infectious disease spread.
BACKGROUND
Assessments of infectious disease spread in hospitals seldom account for interfacility patient sharing. This is particularly important for pathogens with prolonged incubation periods or carrier states.


METHODS
We quantified patient sharing among all 32 hospitals in Orange County (OC), California, using hospital discharge data. Same-day transfers between hospitals were considered "direct" transfers, and events in which patients were shared between hospitals after an intervening stay at home or elsewhere were considered "indirect" patient-sharing events. We assessed the frequency of readmissions to another OC hospital within various time points from discharge and examined interhospital sharing of patients with Clostridium difficile infection.


RESULTS
In 2005, OC hospitals had 319,918 admissions. Twenty-nine percent of patients were admitted at least twice, with a median interval between discharge and readmission of 53 days. Of the patients with 2 or more admissions, 75% were admitted to more than 1 hospital. Ninety-four percent of interhospital patient sharing occurred indirectly. When we used 10 shared patients as a measure of potential interhospital exposure, 6 (19%) of 32 hospitals "exposed" more than 50% of all OC hospitals within 6 months, and 17 (53%) exposed more than 50% within 12 months. Hospitals shared 1 or more patient with a median of 28 other hospitals. When we evaluated patients with C. difficile infection, 25% were readmitted within 12 weeks; 41% were readmitted to different hospitals, and less than 30% of these readmissions were direct transfers.


CONCLUSIONS
In a large metropolitan county, interhospital patient sharing was a potential avenue for transmission of infectious agents. Indirect sharing with an intervening stay at home or elsewhere composed the bulk of potential exposures and occurred unbeknownst to hospitals.
Huang
Susan S
SS
Division of Infectious Diseases and Health Policy Research Institute, University of California Irvine, Irvine, California, USA. susan.huang@uci.edu
Avery
Taliser R
TR
Song
Yeohan
Y
Elkins
Kristen R
KR
Nguyen
Christopher C
CC
Nutter
Sandra K
SK
Nafday
Alaka A
AA
Condon
Curtis J
CJ
Chang
Michael T
MT
Chrest
David
D
Boos
John
J
Bobashev
Georgiy
G
Wheaton
William
W
Frank
Steven A
SA
Platt
Richard
R
Lipsitch
Marc
M
Bush
Robin M
RM
Eubank
Stephen
S
Burke
Donald S
DS
Lee
Bruce Y
BY
D000368:Aged; D002140:California / Q000453:epidemiology; D002648:Child; D015331:Cohort Studies; D003428:Cross Infection / Q000453:epidemiology* / Q000635:transmission*; D005260:Female; D006801:Humans; D008297:Male; D008485:Medical Audit; D008875:Middle Aged; D010351:Patient Discharge; D010360:Patient Transfer; D012189:Retrospective Studies