Incidence of Medically Attended Respiratory Syncytial Virus and Influenza Illnesses in Children 6–59 Months Old During Four Seasons

Simpson, Melissa D.; Kieke, Burney A.; Sundaram, Maria E.; McClure, David L.; Meece, Jennifer K.; Sifakis, Frangiscos; Gasser, Robert A.; Belongia, Edward A.

Seasonal incidence was defined as the number of medically attended cases per 10 000 community residents 6-59 months old. All incidence estimates were standardized to weeks 40 through 18 (31 weeks from early October through early May) using Wisconsin State Laboratory of Hygiene surveillance data for RSV and influenza [16] . Incidence calculations were based on 2 assumptions. First, we assumed that test results from enrolled patients with MAARI can be extrapolated to nonenrolled cohort members with a respiratory illness visit during the enrollment period. Visits for ARI were based on ICD-9 codes (specific codes available on request). Although rare, some study participants did not receive a diagnosis code for ARI because enrollment eligibility was based on presenting symptoms rather than ICD-9 codes that were assigned after the visit. Test results for these participants were not extrapolated to nonenrolled cohort members.