Estimating the hospitalization burden associated with influenza and respiratory syncytial virus in New York City, 2003-2011.BACKGROUND
 Hospitalization burden associated with influenza and respiratory syncytial virus (RSV) is uncertain due to ambiguity in the inference methodologies employed for its estimation.


 Utilization of a new method to quantitate the above burden.


 Weekly hospitalization rates for several principal diagnoses from 2003 to 2011 in New York City by age group were regressed linearly against incidence proxies for the major influenza subtypes and RSV adjusting for temporal trends and seasonal baselines.


 RESULTS
 Average annual rates of influenza-associated respiratory hospitalizations per 100 000 were estimated to be 129 [95% CI (79, 179)] for age <1, 36·3 (21·6, 51·4) for ages 1-4, 10·6 (7·5, 13·7) for ages 5-17, 25·6 (21·3, 29·8) for ages 18-49, 65·5 (54·0, 76·9) for ages 50-64, 125 (105, 147) for ages 65-74, and 288 (244, 331) for ages ≥75.  Additionally, influenza had a significant contribution to hospitalization rates with a principal diagnosis of septicemia for ages 5-17 [0·76 (0·1, 1·4)], 18-49 [1·02 (0·3, 1·7)], 50-64 [4·0 (1·7, 6·3)], 65-74 [8·8 (2·2, 15·6)], and ≥75 [38·7 (25·7, 52·9)].  RSV had a significant contribution to the rates of respiratory hospitalizations for age <1 [1900 (1740, 2060)], ages 1-4 [117 (70, 167)], and ≥75 [175 (44, 312)] [including chronic lower respiratory disease, 90 (43, 140)] as well as pneumonia & influenza hospitalizations for ages 18-49 [6·2 (1·1, 11·3)] and circulatory hospitalizations for ages ≥75 [199 (13, 375)].


 The high burden of RSV hospitalizations among young children and seniors age ≥75 suggests the need for additional control measures such as vaccination to mitigate the impact of annual RSV epidemics.  Our estimates for influenza-associated hospitalizations provide further evidence of the burden of morbidity associated with influenza, supporting current guidelines regarding influenza vaccination and antiviral treatment.
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