Background: Young children are at increased risk of severe outcomes from influenza illness, including hospitalization. We conducted a case-control study to identify risk factors for influenza-associated hospitalizations among children in US Emerging Infections Program sites.
Methods: Cases were children 6–59 months of age hospitalized for laboratory-confirmed influenza infections during 2005–2008. Age- and zip-code-matched controls were enrolled. Data on child, caregiver and household characteristics were collected from parents and medical records. Conditional logistic regression was used to identify independent risk factors for hospitalization.
Results: We enrolled 290 (64%) of 454 eligible cases and 1089 (49%) of 2204 eligible controls. Risk for influenza hospitalization increased with maternal age <26 years [odds ratio (OR): 1.8, 95% confidence interval (CI): 1.1–2.9]; household income below the poverty threshold (OR: 2.2, 95% CI: 1.4–3.6); smoking by >50% of household members (OR: 2.9, 95% CI: 1.4–6.6); lack of household influenza vaccination (OR: 1.8, 95% CI: 1.2–2.5) and presence of chronic illnesses, including hematologic/oncologic (OR: 11.8, 95% CI: 4.5–31.0), pulmonary (OR: 2.9, 95% CI: 1.9–4.4) and neurologic (OR: 3.8, 95% CI: 1.6–9.2) conditions. Full influenza immunization decreased the risk among children 6–23 months of age (OR: 0.5, 95% CI: 0.3–0.9) but not among those 24–59 months of age (OR: 1.5, 95% CI: 0.8–3.0; P value for difference = 0.01).
Conclusions: Chronic illnesses, young maternal age, poverty, household smoking and lack of household influenza vaccination increased the risk of influenza hospitalization. These characteristics may help providers to identify young children who are at greatest risk for severe outcomes from influenza illness.
From the *Influenza Division, Centers for Disease Control and Prevention; †Battelle Memorial Institute, Atlanta, GA; ‡Colorado Department of Public Health and Environment, Denver, CO; §Minnesota Department of Health, St. Paul, MN; ¶Oregon Public Health Division, Portland, OR; ‖Connecticut Emerging Infections Program, New Haven, CT; **Emory University School of Medicine and the Atlanta VA Medical Center; ††Georgia Emerging Infections Program, Atlanta, GA; ‡‡California Emerging Infections Program, Oakland, CA; §§Tennessee Department of Health; ¶¶Department of Preventive Medicine, Vanderbilt University School of Medicine, Nashville, TN; ‖‖University of Rochester School of Medicine and Dentistry, Rochester; ***New York State Department of Health, Albany, NY; †††New Mexico Department of Health, Santa Fe; and ‡‡‡University of New Mexico, Albuquerque, NM.
Accepted for publication December 23, 2013.
N.J.D. is currently at the Department of Medicine, New Jersey Medical School, Newark, NJ.
A.S.C. is currently Resident Advisor/President’s Malaria Initiative, Center for Global Health, Division of Parasitic Diseases and Malaria, Malaria Branch.
The EIP is a collaboration of state health departments, academic institutions and local partners and is funded by the Centers for Disease Control and Prevention. Members of the EIP sites were involved in the design and conduct of the study; collection, management, analysis and interpretation of the data and preparation, review or approval of the manuscript.
Preliminary results of this study were presented in an oral session at the 2010 Infectious Diseases Society of America: Nila J. Dharan, Leslie Z. Sokolow, Po-Yung Cheng, Paul Gargiullo, Laurie Kamimoto, Art Reingold, Ken Gershman, James Meek, Monica Farley, Kathryn Arnold, Ruth Lynfield, Joan Baumbach, Sarah Lathrop, Nancy M. Bennett, Shelley Zansky, Ann Thomas, William Schaffner, David Kirschke and David K. Shay. Child and household risk factors for hospitalization with laboratory-confirmed influenza among children aged 6–59 months—United States, 2005–2008. Presented by N. Dharan, IDSA Annual Meeting, October 23, 2010, Vancouver, Canada.
W.S. has the following disclosures: Member, DSMB for Merck and Sanofi-Pasteur; occasional consultant for Pfizer, Novartis, GSK and Dynavax. The other authors have no other funding or conflicts of interest to disclose.
Address for correspondence: Nila J. Dharan, MD, Department of Medicine, New Jersey Medical School, 185 South Orange Avenue, MSB I-689, Newark, NJ 07103. E-mail: Dharannj@njms.rutgers.edu.
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