The underrecognized burden of influenza in young children

N Engl J Med. 2006 Jul 6;355(1):31-40. doi: 10.1056/NEJMoa054869.


Background: The disease burden of influenza infection among children is not well established. We conducted a population-based surveillance of medical visits associated with laboratory-confirmed influenza.

Methods: Eligible children were younger than five years of age, resided in three U.S. counties, and had a medical visit for an acute respiratory tract infection or fever. Nasal and throat swabs were tested for the influenza virus by viral culture and polymerase-chain-reaction assay. Epidemiologic data were collected from parental surveys and chart reviews. Children who were hospitalized were enrolled prospectively from 2000 through 2004. Population-based rates of hospitalizations associated with influenza were calculated. Children who were seen in selected pediatric clinics and emergency departments during two influenza seasons (2002-2003 and 2003-2004) were systematically enrolled. The rates of visits to clinics and emergency departments associated with influenza were estimated.

Results: The average annual rate of hospitalization associated with influenza was 0.9 per 1000 children. The estimated burden of outpatient visits associated with influenza was 50 clinic visits and 6 emergency department visits per 1000 children during the 2002-2003 season and 95 clinic visits and 27 emergency department visits per 1000 children during the 2003-2004 season. Few children who had laboratory-confirmed influenza were given a diagnosis of influenza by the treating physician in the inpatient (28 percent) or outpatient (17 percent) settings.

Conclusions: Among young children, outpatient visits associated with influenza were 10 to 250 times as common as hospitalizations. Few influenza infections were recognized clinically.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Ambulatory Care / statistics & numerical data*
  • Child, Preschool
  • Emergency Medical Services / statistics & numerical data
  • Female
  • Hospitalization / statistics & numerical data*
  • Humans
  • Infant
  • Influenza Vaccines
  • Influenza, Human / diagnosis
  • Influenza, Human / epidemiology*
  • Male
  • Population Surveillance
  • Prospective Studies
  • United States / epidemiology


  • Influenza Vaccines