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.

In each season, 29% to 48% of children in the community cohorts had a MAARI visit ( Table 2 ). We enrolled and tested 40% to 57% of MAARI cases. The overall estimated seasonal incidence of medically attended RSV was 1718 cases per 10 000 (95% CI, 1602-1843) from week 40 through week 18 ( Table 3 ). The seasonal incidence was highest in 2007-2008 and lowest in 2006-2007. Figure 1 shows seasonal incidence and 95% confidence limits by season and age group. With the exception of 2008-2009, the seasonal incidence was similar in the 6-11 month and 12-23 month age groups. Incidence in the 24-59 month age group was substantially lower than the other age groups in all seasons. Based on pairwise comparisons between age groups, across all seasons, the seasonal RSV incidence differed marginally between the 6-11 month age group and the 12-23 month age group (P = .05), and the incidence in both of these age groups was significantly higher than in the 24-59 month age group (P < .0001 for both comparisons).