  Background: There is uncertainty about the burden of severe outcomes
associated with RSV and influenza in children.
  Methods: We have applied previously developed methodology to estimate the
rates of influenza and RSV-associated hospitalizations with different diagnoses
in different age subgroups of US children between the 2003-04 through the
2009-10 seasons.
  Results: The average annual rates (per 100,000) of influenza and
RSV-associated hospitalizations for any cause excluding asthma (ICD-9 code 493)
in the principal diagnosis with a respiratory cause (ICD-9 codes 460-519) in
the diagnosis (either principal or secondary) were 173.1(95%CI (134.3,212.6))
(influenza) vs. 2336(2209,2463) (RSV) (age <1y); 77.9(51.1,105.2) vs.
625.7(540,711.5) (age 1y); 56.3(40.9,72.2) vs. 324.2(275.1,375) (age 2y);
44.6(32.9,56.6) vs. 172.2(134.2,211) (age 3y); 36.4(27.7,45.3) vs.
89.7(60.6,117.8) (age 4y); 36.6(29.3,43.9) vs. 62.3(38.8,86.4) (ages 5-6y);
20.5(16.3,24.6) vs. 30.2(16.1,43.9) (ages 7-11y); and 16.1(10.6,21.7) vs.
36.9(17.8,55.9) (ages 12-17y). The rates of RSV-associated hospitalizations
with asthma as a secondary (non-principal) diagnosis were 162.6(143.6,181.6)
(age <1y), 144.7(120.8,168.2) (age 1y), 99.5(82.3,116.8) (age 2y),
60.9(46.4,75.3) (age 3y), 23.5(10.7,36.4) (age 4y), 16.1(5.1,27) (ages 5-6y),
11.4(4.7,18.3) (ages 7-11y), and 15.8(4.9,26.7) (ages 12-17y).
  Conclusions: The estimated rates of RSV-associated hospitalizations in young
children are high, with those rates declining rapidly with age. Additionally,
the estimated rates of RSV-associated hospitalizations with asthma as a
secondary diagnosis in young children, combined with data on the prevalence of
asthma in those age groups suggest very high rates of RSV-associated
hospitalizations in young children with asthma. Those children may be
considered as potential target groups for RSV-related mitigation efforts.
