Background: Little information is available describing the epidemiology and clinical characteristics of those <12 months hospitalized with influenza, particularly at a population level.
Methods: We used population-based, laboratory-confirmed influenza hospitalization surveillance data from 2003 to 2012 seasons to describe the impact of influenza by age category (<3, 3 to <6 and 6 to <12 months). Logistic regression was used to explore risk factors for intensive care unit (ICU) admission. Adjusted age-specific, influenza-associated hospitalization rates were calculated and applied to the number of US infants to estimate national numbers of hospitalizations.
Results: Influenza was associated with an annual average of 6514 infant hospitalizations (range 1842–12,502). Hospitalization rates among infants <3 months were substantially higher than the rate in older infants. Most hospitalizations occurred in otherwise healthy infants (75%) among whom up to 10% were admitted to the ICU and up to 4% had respiratory failure. These proportions were 2–3 times higher in infants with high risk conditions. Infants <6 months were 40% more likely to be admitted to the ICU than older infants. Lung disease (adjusted odds ratio 1.80; 95% confidence interval 1.22–2.67), cardiovascular disease (adjusted odds ratio: 4.16; 95% confidence interval: 2.65–6.53), and neuromuscular disorder (adjusted odds ratio: 2.99; 95% confidence interval: 1.87–4.78) were risk factors for ICU admission among all infants.
Conclusions: The impact of influenza on infants, particularly those very young or with high risk conditions, underscores the importance of influenza vaccination, especially among pregnant women and those in contact with young infants not eligible for vaccination.
From the *Centers for Disease Control and Prevention; †Emory University School of Medicine; ‡Atlanta Veterans Administration Medical Center, Atlanta, GA; §Colorado Department of Public Health and Environment, Denver, CO; ¶Department of Preventive Medicine, Vanderbilt University School of Medicine, Nashville, TN; ‖Michigan Department of Community Health, Lansing, MI; **Connecticut Emerging Infections Program, School of Public Health, New Haven, CT; ††Oregon Public Health Division, Portland, OR; ‡‡Utah Department of Health, Salt Lake City, UT; §§New Mexico Department of Health, Santa Fe, NM; ¶¶Rhode Island Department of Health, Providence, RI; ‖‖Minnesota Department of Health, St. Paul, MN; ***Emerging Infections Program, New York State Department of Health, Albany, NY; †††California Emerging Infections Program, Oakland, CA; ‡‡‡Department of Medicine, University of Rochester School of Medicine and Dentistry; §§§Monroe County, Department of Public Health, Rochester, NY; ¶¶¶Maryland Department of Health and Mental Hygiene, Baltimore, MD; and ‖‖‖Ohio Department of Health, Columbus, OH.
Accepted for publication February 21, 2014.
Ruta Sharangpani, MD, is currently at the Wayne County Department of Public Health, Wayne, MI.
Ananda S. Bandyopadhyay, MB BS, MPH, is currently a Program Officer at The Bill and Melinda Gates Foundation.
The Influenza Hospitalization Surveillance Network (FluSurv-NET) is a collaboration of state health departments, academic institutions and local partners and is funded by the CDC. This publication was supported in part by Cooperative Agreement number CDC-RFA-CK12-1202 and 5U38HM000414 from the CDC.
W.S. is a data safety monitoring board member for Merck and Sanofi-Pasteur and occasionally consults for Pfizer, GlasoSmithKline and Dynavax. The authors have no other funding or conflicts of interest to disclose.
The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the CDC or the US Department of Health and Human Services.
Address for correspondence: Sandra S. Chaves, MD, MSc, 1600 Clifton Road, NE; Mailstop A-20, Atlanta, GA 30333. E-mail: email@example.com.