Novel inpatient surveillance in tertiary paediatric hospitals in New South Wales illustrates impact of first-wave pandemic influenza A H1N1 (2009) and informs future health service planning

Aim: To document the impact of pandemic influenza A H1N1 (2009) in New South Wales (NSW) children's hospitals.

Methods: A novel surveillance system, Paediatric Active Enhanced Disease Surveillance (PAEDS), identified hospitalised children <15 years with laboratory-proven influenza (1 June-30 September 2009) in the three children's hospitals in NSW: Children's Hospital at Westmead (CHW), Sydney Children's Hospital, John Hunter Children's Hospital. Clinical characteristics, management and complications were documented, and at CHW comparison made with 2007 data.

Results: The 324 children identified represented 1802 hospital bed-days and 230 PICU bed-days. Most (73.1%) children had H1N1, one had an oseltamivir-resistant isolate. Median age was 2.5 years: 65% were <5 years. Although 80.9% had cough, 8.0% had no respiratory symptoms. Complications occurred in 34.6%, of whom 56% were previously healthy. Only 50% received antivirals. Forty children (12.3%) were admitted to PICU: one child with H1N1 died. At CHW, comparison between 2009 and 2007 showed nearly twice the total number of admissions (226 vs. 122) and PICU admissions (22 vs. 13), but no deaths either year. Vomiting was more frequent in 2009 than 2007 (38.5% vs. 13.1%; P = 0.0001) as were neurological complications (11.4% vs. 2.4%; P = 0.0027) but length of hospital and PICU stay were similar.

Conclusions: PAEDS is a valuable surveillance tool that documented the impact of the H1N1 (2009) pandemic in NSW children's hospitals. High numbers of complications, often in previously well children, suggest an important role for early diagnosis, antiviral therapy and influenza vaccination. Observed regional differences identify areas potentially at greater risk in a subsequent wave.