  Emergent antibiotic-resistant bacterial infections are an increasingly
significant source of morbidity and mortality. Antibiotic-resistant organisms
have a natural reservoir in hospitals, and recent estimates suggest that almost
2 million people develop hospital-acquired infections each year in the US
alone. We investigate a network induced by the transfer of Medicare patients
across US hospitals over a 2-year period to learn about the possible role of
hospital-to-hospital transfers of patients in the spread of infections. We
analyze temporal, geographical, and topological properties of the transfer
network and demonstrate, using C. Diff. as a case study, that this network may
serve as a substrate for the spread of infections. Finally, we study different
strategies for the early detection of incipient epidemics, finding that using
approximately 2% of hospitals as sensors, chosen based on their network
in-degree, results in optimal performance for this early warning system,
enabling the early detection of 80% of the C. Diff. cases.
