American Journal of Infection Control
Vol 42 | No. 1 | January 2014 | Pages 1-92
http://www.ajicjournal.org/current

Hospital-onset influenza hospitalizations—United States, 2010-2011
Michael A. Jhung, MD, Tiffany D’Mello, MPH, Alejandro Pérez, MPH, Deborah Aragon, MSPH,
Nancy M. Bennett, MD, Tara Cooper, MPH, Monica M. Farley, MD, Brian Fowler, MPH, Stephen M. Grube, MD, Emily B. Hancock, MS, Ruth Lynfield, MD, Craig Morin, MPH, Arthur Reingold, MD, Patricia Ryan, MS, William Schaffner, MD, Ruta Sharangpani, MD, Leslie Tengelsen, PhD,
Ann Thomas, MD, Diana Thurston, PhD, Kimberly Yousey-Hindes, MPH Shelley Zansky, PhD, Lyn Finelli, DrPH, Sandra S. Chaves, MD
published online 01 November 2013.
http://www.ajicjournal.org/article/S0196-6553%2813%2901098-5/abstract

Abstract
Background
Seasoaal influenza is responsible for more than 200,000 hospitalizations each year in the United States. Although hospital-onset (HO) influenza contributes to morbidity and mortality among these patients, little is known about its overall epidemiology.

Objective
We describe patients with HO influenza in the United States during the 2010-2011 influenza season and compare them with community-onset (CO) cases to better understand factors associated with illness.

Methods
We identified laboratory-confirmed, influenza-related hospitalizations using the Influenza Hospitalization Surveillance Network (FluSurv-NET), a network that conducts population-based surveillance in 16 states. CO cases had laboratory confirmation ≤ 3 days after hospital admission; HO cases had laboratory confirmation > 3 days after admission.

Results
We identified 172 (2.8%) HO cases among a total of 6,171 influenza-positive hospitalizations. HO and CO cases did not differ by age (P = .22), sex (P = .29), or race (P = .25). Chronic medical conditions were more common in HO cases (89%) compared with CO cases (78%) (P < .01), and a greater proportion of HO cases (42%) than CO cases (17%) were admitted to the intensive care unit (P < .01). The median length of stay after influenza diagnosis of HO cases (7.5 days) was greater than that of CO cases (3 days) (P < .01).

Conclusion
HO cases had greater length of stay and were more likely to be admitted to the intensive care unit or die compared with CO cases. HO influenza may play a role in the clinical outcome of hospitalized patients, particularly among those with chronic medical conditions.