9) and y is the admissions to public HA hospitals as a percentage of total admissions by age (Appendix 1). These proportions were weighted by the number of admissions when incidence estimates were calculated for different age groups: ∑j(Admissionsj×Pj)∑jAdmissionsjwhere Admissionsj is the number of admissions in the jth age group, and Pj is the proportion of admissions to HA hospitals Selleck Apoptosis Compound Library in the jth age group; z is the estimated resident population by age (Appendix 2). Incidence rates were calculated by monthly age

groups and then re-grouped according to different age ranges (Table 1). Since a CMS flu diagnosis may reflect both under- and over-diagnosis, we applied adjustment factors to this CMS Flu derived incidence estimate (Table 1). These factors were derived by linking the PWH laboratory surveillance data (LAB flu+ or LAB flu−) with the PWH CMS data (CMS flu+ or CMS flu−) (Appendix 3). The first factor was derived to adjust for potential under-reporting of influenza infection by the CMS system. The second factor was derived to reflect the potential under-estimation of a PWH laboratory diagnosis of influenza by accounting for the fact that not all admissions with a primary respiratory-associated diagnosis had a NPA specimen sent to the laboratory for testing. The third factor was the PLX4032 proportion of all admissions to PWH by age group

that had a laboratory confirmed diagnosis of influenza. No assessment or adjustment was made for possible nosocomial infections. During the 6-year study tuclazepam period 1 April 2005 to 31 March 2011, there were 624,916 children admitted to the paediatric medical wards of all HA hospitals; 2 had no gender specified and 86 had missing age data and were excluded. Of the 624,828 children with valid data, 94.5% (590,683) were below the age of 18 years and 32.9% (205,783) were below the age of

6 months, 13.9% (86,582) were aged above 6 days to below 6 months (6M group) and 75.5% (471,482) were aged above 6 days to below 18 years (18Y group). In the 6M and 18Y groups respiratory-associated disorders were respectively coded as the primary diagnosis in 13.9% and 27.2% of admissions, and as the primary or as one of any 9 secondary diagnoses in 15.7% and 31.8% (Appendix 4). The percentage of all discharges with a primary diagnosis and “any” diagnosis of influenza (CMS flu) ranged from 0.3% to 1.4% and 0.4 to 1.9% in the 6M group and from 0.9% to 4.2% and 1.3% to 6.0% in the 18Y group respectively in the 12 HA hospitals (Appendix 5). Likewise rates of admissions coded as having a respiratory illness varied considerably between these different hospitals. Influenza admissions peaked during February and September (Fig. 1). Over the full 6 year study period there was a peak of admissions during the April 2009–March 2010 (Fig. 1). A similar pattern was seen with the data from all HA hospitals and with data from PWH alone (Fig. 1).